Karen Day, Ph.D.

The Stability and Complexity of Antibody Responses to the Major Surface Antigen of Plasmodium falciparum Are Associated with Age in a Malaria Endemic Area
Barry, Alyssa E.; Trieu, Angela; Fowkes, Freya J. I.; Pablo, Jozelyn; Kalantari-Dehaghi, Mina; Jasinskas, Algis; Tan, Xiaolin; Kayala, Matthew A.; Tavul, Livingstone; Siba, Peter M.; Day, Karen P.; Baldi, Pierre; Felgner, Philip L.; Doolan, Denise L.
2011 NOV ;10(11):-, Molecular & cellular proteomics
Individuals that are exposed to malaria eventually develop immunity to the disease with one possible mechanism being the gradual acquisition of antibodies to the range of parasite variant surface antigens in their local area. Major antibody targets include the large and highly polymorphic Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) family of proteins. Here, we use a protein microarray containing 123 recombinant PfEMP1-DBL alpha domains (VAR) from Papua New Guinea to seroprofile 38 nonimmune children (<4 years) and 29 hyperimmune adults (>= 15 years) from the same local area. The overall magnitude, prevalence and breadth of antibody response to VAR was limited at <2 years and 2-2.9 years, peaked at 3-4 years and decreased for adults compared with the oldest children. An increasing proportion of individuals recognized large numbers of VAR proteins (>20) with age, consistent with the breadth of response stabilizing with age. In addition, the antibody response was limited in uninfected children compared with infected children but was similar in adults irrespective of infection status. Analysis of the variant-specific response confirmed that the antibody signature expands with age and infection. This also revealed that the antibody signatures of the youngest children overlapped substantially, suggesting that they are exposed to the same subset of PfEMP1 variants. VAR proteins were either seroprevalent from early in life, (<3 years), from later in childhood (>= 3 years) or rarely recognized. Group 2 VAR proteins (Cys2/MFK-REY+) were serodominant in infants (<1-year-old) and all other sequence subgroups became more seroprevalent with age. The results confirm that the anti-PfEMP1-DBL alpha antibody responses increase in magnitude and prevalence with age and further demonstrate that they increase in stability and complexity. The protein microarray approach provides a unique platform to rapidly profile variant-specific antibodies to malaria and suggests novel insights into the acquisition of immunity to malaria. Molecular & Cellular Proteomics 10: 10.1074/mcp.M111.008326, 1-12, 2011
— id: 141779, year: 2011, vol: 10, page: , stat: Journal Article,

Maternal anemia in benin: prevalence, risk factors, and association with low birth weight
Bodeau-Livinec, Florence; Briand, Valerie; Berger, Jacques; Xiong, Xu; Massougbodji, Achille; Day, Karen P; Cot, Michel
2011 Sep;85(3):414-420, American journal of tropical medicine & hygiene
Abstract. We studied the prevalence of anemia during pregnancy and its relationship with low birth weight (LBW; birth weight < 2,500 g) in Benin. We analyzed 1,508 observations from a randomized controlled trial conducted from 2005 to 2008 showing equivalence on the risk of LBW between two drugs for Intermittent Preventive Treatment of malaria during pregnancy (IPTp). Despite IPTp, helminth prophylaxis, and iron and folic acid supplementations, the proportions of women with severe anemia (hemoglobin [Hb] concentration < 80 g/L) and anemia (Hb < 110 g/L) were high throughout pregnancy: 3.9% and 64.7% during the second and 3.7% and 64.1% during the third trimester, but 2.5% and 39.6% at the onset of labor, respectively. Compared with women without anemia (Hb >/= 110 g/L) during the third trimester, women with severe anemia (Hb < 80 g/L) were at higher risk of LBW after adjustment for potential confounding factors (prevalence ratio [PR] = 2.8; 95% confidence interval [1.4-5.6])
— id: 137446, year: 2011, vol: 85, page: 414, stat: Journal Article,

A Molecular Epidemiological Study of var Gene Diversity to Characterize the Reservoir of Plasmodium falciparum in Humans in Africa
Chen, Donald S; Barry, Alyssa E; Leliwa-Sytek, Aleksandra; Smith, Terry-Ann; Peterson, Ingrid; Brown, Stuart M; Migot-Nabias, Florence; Deloron, Philippe; Kortok, Moses M; Marsh, Kevin; Daily, Johanna P; Ndiaye, Daouda; Sarr, Ousmane; Mboup, Souleymane; Day, Karen P
2011 ;6(2):e16629-e16629, PLoS ONE
BACKGROUND: The reservoir of Plasmodium infection in humans has traditionally been defined by blood slide positivity. This study was designed to characterize the local reservoir of infection in relation to the diverse var genes that encode the major surface antigen of Plasmodium falciparum blood stages and underlie the parasite's ability to establish chronic infection and transmit from human to mosquito. METHODOLOGY/PRINCIPAL FINDINGS: We investigated the molecular epidemiology of the var multigene family at local sites in Gabon, Senegal and Kenya which differ in parasite prevalence and transmission intensity. 1839 distinct var gene types were defined by sequencing DBLalpha domains in the three sites. Only 76 (4.1%) var types were found in more than one population indicating spatial heterogeneity in var types across the African continent. The majority of var types appeared only once in the population sample. Non-parametric statistical estimators predict in each population at minimum five to seven thousand distinct var types. Similar diversity of var types was seen in sites with different parasite prevalences. CONCLUSIONS/SIGNIFICANCE: Var population genomics provides new insights into the epidemiology of P. falciparum in Africa where malaria has never been conquered. In particular, we have described the extensive reservoir of infection in local African sites and discovered a unique var population structure that can facilitate superinfection through minimal overlap in var repertoires among parasite genomes. Our findings show that var typing as a molecular surveillance system defines the extent of genetic complexity in the reservoir of infection to complement measures of malaria prevalence. The observed small scale spatial diversity of var genes suggests that var genetics could greatly inform current malaria mapping approaches and predict complex malaria population dynamics due to the import of var types to areas where no widespread pre-existing immunity in the population exists
— id: 124110, year: 2011, vol: 6, page: e16629, stat: Journal Article,

Microbiology. Quantifying malaria dynamics within the host
Day, Karen P; Fowkes, Freya J I
2011 Aug 19;333(6045):943-944, Science
— id: 136944, year: 2011, vol: 333, page: 943, stat: Journal Article,

ANEMIA DURING PREGNANCY AND LOW BIRTH WEIGHT IN AN ENDEMIC MALARIA AREA IN BENIN
Bodeau-Livinec, F; Briand, V; Berger, J; Xiong, X; Day, KR; Massougbodgi, A; Cot, M
2009 NOV ;81(5):41-41, American journal of tropical medicine & hygiene
— id: 106985, year: 2009, vol: 81, page: 41, stat: Journal Article,

The acute phase response in children with mild and severe malaria in Papua New Guinea
O'Donnell, Angela; Fowkes, Freya J I; Allen, Stephen J; Imrie, Heather; Alpers, Michael P; Weatherall, David J; Day, Karen P
2009 Jul;103(7):679-686, Transactions of the Royal Society of Tropical Medicine & Hygiene
The production of acute phase proteins during infection is an important part of innate immunity and limits inflammation. However, little is known of the acute phase response in malaria. We measured acute phase proteins in plasma in children attending clinics and admitted to hospital with acute malaria in Papua New Guinea. Plasma ferritin concentration increased progressively with disease severity with markedly elevated levels in the most severely ill children. Plasma ferritin was >500 ng/ml in 7/99 (7.1%) outpatients with uncomplicated malaria, 22/100 (22.0%) hospital non-severe cases, 64/175 (36.6%) severe malaria cases who survived and 7/9 (77.8%) severe malaria deaths (P<0.001). The greatest concentration of ferritin (3561 ng/ml) was observed in a child who died. By contrast, C-reactive protein concentration was markedly increased in 153 children with uncomplicated malaria [median 203 (interquartile range 51-365) microg/ml] but, surprisingly, was only moderately increased in 135 children with one or more severe manifestations of malaria [47 (17-97) microg/ml; P<0.001] and in 6 children who died [41 (22-280) microg/ml]. Excessive free-radical damage resulting from a combination of iron-induced oxidant stress and reduced levels of C-reactive protein may be an important pathological mechanism in severe malaria and amenable to therapeutic intervention
— id: 115361, year: 2009, vol: 103, page: 679, stat: Journal Article,

Uric acid is a mediator of the Plasmodium falciparum-induced inflammatory response
Orengo, Jamie Marie; Leliwa-Sytek, Aleksandra; Evans, James E; Evans, Barbara; van de Hoef, Diana; Nyako, Marian; Day, Karen; Rodriguez, Ana
2009 ;4(4):e5194-e5194, PLoS ONE
BACKGROUND: Malaria triggers a high inflammatory response in the host that mediates most of the associated pathologies and contributes to death. The identification of pro-inflammatory molecules derived from Plasmodium is essential to understand the mechanisms of pathogenesis and to develop targeted interventions. Uric acid derived from hypoxanthine accumulated in infected erythrocytes has been recently proposed as a mediator of inflammation in rodent malaria. METHODS AND FINDINGS: We found that human erythrocytes infected with Plasmodium falciparum gradually accumulate hypoxanthine in their late stages of development. To analyze the role of hypoxanthine-derived uric acid induced by P. falciparum on the inflammatory cytokine response from human blood mononuclear cells, cultures were treated with allopurinol, to inhibit uric acid formation from hypoxanthine, or with uricase, to degrade uric acid. Both treatments significantly reduce the secretion of TNF, IL-6, IL-1beta and IL-10 from human cells. CONCLUSIONS AND SIGNIFICANCE: Uric acid is a major contributor of the inflammatory response triggered by P. falciparum in human peripheral blood mononuclear cells. Since the inflammatory reaction induced by P. falciparum is considered a major cause of malaria pathogenesis, identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease
— id: 99008, year: 2009, vol: 4, page: e5194, stat: Journal Article,

Geographic population structure of the immune evasion (var) genes of Plasmodium falciparum
Barry, AE; Smith, TA; Chen, D; Sytek, AL; Imrie, H; Tavul, L; Migot-Nabias, F; Brown, SM; Deloron, P; Daily, J; Marsh, K; McVean, G; Day, KP
2008 JAN ;38(1):S38-S39, International journal for parasitology
— id: 76166, year: 2008, vol: 38, page: S38, stat: Journal Article,

Seasonal variation in Plasmodium prevalence in a population of blue tits Cyanistes caeruleus
Cosgrove, Catherine L; Wood, Matthew J; Day, Karen P; Sheldon, Ben C
2008 May;77(3):540-548, Journal of animal ecology
1. Seasonal variation in environmental conditions is ubiquitous and can affect the spread of infectious diseases. Understanding seasonal patterns of disease incidence can help to identify mechanisms, such as the demography of hosts and vectors, which influence parasite transmission dynamics. 2. We examined seasonal variation in Plasmodium infection in a blue tit Cyanistes caeruleus population over 3 years using sensitive molecular diagnostic techniques, in light of Beaudoin et al.'s (1971; Journal of Wildlife Diseases, 7, 5-13) model of seasonal variation in avian malaria prevalence in temperate areas. This model predicts a within-year bimodal pattern of spring and autumn peaks with a winter absence of infection. 3. Avian malaria infections were mostly Plasmodium (24.4%) with occasional Haemoproteus infections (0.8%). Statistical nonlinear smoothing techniques applied to longitudinal presence/absence data revealed marked temporal variation in Plasmodium prevalence, which apparently showed a within-year bimodal pattern similar to Beaudoin et al.'s model. However, of the two Plasmodium morphospecies accounting for most infections, only the seasonal pattern of Plasmodium circumflexum supported Beaudoin et al.'s model. On closer examination there was also considerable age structure in infection: Beaudoin et al.'s seasonal pattern was observed only in first year and not older birds. Plasmodium relictum prevalence was less seasonally variable. 4. For these two Plasmodium morphospecies, we reject Beaudoin et al.'s model as it does not survive closer scrutiny of the complexities of seasonal variation among Plasmodium morphospecies and host age classes. Studies of host-parasite interactions should consider seasonal variation whenever possible. We discuss the ecological and evolutionary implications of seasonal variation in disease prevalence
— id: 78764, year: 2008, vol: 77, page: 540, stat: Journal Article,

Increased microerythrocyte count in homozygous alpha(+)-thalassaemia contributes to protection against severe malarial anaemia
Fowkes, Freya J I; Allen, Stephen J; Allen, Angela; Alpers, Michael P; Weatherall, David J; Day, Karen P
2008 Mar 18;5(3):e56-e56, PLoS medicine
BACKGROUND: The heritable haemoglobinopathy alpha(+)-thalassaemia is caused by the reduced synthesis of alpha-globin chains that form part of normal adult haemoglobin (Hb). Individuals homozygous for alpha(+)-thalassaemia have microcytosis and an increased erythrocyte count. Alpha(+)-thalassaemia homozygosity confers considerable protection against severe malaria, including severe malarial anaemia (SMA) (Hb concentration < 50 g/l), but does not influence parasite count. We tested the hypothesis that the erythrocyte indices associated with alpha(+)-thalassaemia homozygosity provide a haematological benefit during acute malaria. METHODS AND FINDINGS: Data from children living on the north coast of Papua New Guinea who had participated in a case-control study of the protection afforded by alpha(+)-thalassaemia against severe malaria were reanalysed to assess the genotype-specific reduction in erythrocyte count and Hb levels associated with acute malarial disease. We observed a reduction in median erythrocyte count of approximately 1.5 x 10(12)/l in all children with acute falciparum malaria relative to values in community children (p < 0.001). We developed a simple mathematical model of the linear relationship between Hb concentration and erythrocyte count. This model predicted that children homozygous for alpha(+)-thalassaemia lose less Hb than children of normal genotype for a reduction in erythrocyte count of >1.1 x 10(12)/l as a result of the reduced mean cell Hb in homozygous alpha(+)-thalassaemia. In addition, children homozygous for alpha(+)-thalassaemia require a 10% greater reduction in erythrocyte count than children of normal genotype (p = 0.02) for Hb concentration to fall to 50 g/l, the cutoff for SMA. We estimated that the haematological profile in children homozygous for alpha(+)-thalassaemia reduces the risk of SMA during acute malaria compared to children of normal genotype (relative risk 0.52; 95% confidence interval [CI] 0.24-1.12, p = 0.09). CONCLUSIONS: The increased erythrocyte count and microcytosis in children homozygous for alpha(+)-thalassaemia may contribute substantially to their protection against SMA. A lower concentration of Hb per erythrocyte and a larger population of erythrocytes may be a biologically advantageous strategy against the significant reduction in erythrocyte count that occurs during acute infection with the malaria parasite Plasmodium falciparum. This haematological profile may reduce the risk of anaemia by other Plasmodium species, as well as other causes of anaemia. Other host polymorphisms that induce an increased erythrocyte count and microcytosis may confer a similar advantage
— id: 78763, year: 2008, vol: 5, page: e56, stat: Journal Article,

Alpha+ -thalassaemia and malaria in Melanesia: epidemiological perspectives
Fowkes, Freya J I; Day, Karen P
2008 Sep-Dec;51(3-4):131-137, Papua & New Guinea medical journal
In 1948 Haldane first proposed that the high frequencies of thalassaemias in malaria-endemic regions were due to natural selection by malaria. Some of the highest frequencies of alpha+ -thalassaemia are found in the Pacific region of Melanesia. Consequently, Melanesia has provided a unique opportunity for an extensive study of the association between alpha+ -thalassaemia and malaria. Here we review the emergence of alpha+ -thalassaemia in this region and the research that has been carried out, both from the historical perspective and the most recent developments, which may give insight into the selection of alpha+ -thalassaemia by malaria
— id: 115362, year: 2008, vol: 51, page: 131, stat: Journal Article,

Host erythrocyte polymorphisms and exposure to Plasmodium falciparum in Papua New Guinea
Fowkes, Freya J I; Michon, Pascal; Pilling, Lynn; Ripley, Ruth M; Tavul, Livingstone; Imrie, Heather J; Woods, Caira M; Mgone, Charles S; Luty, Adrian J F; Day, Karen P
2008 ;7:1-1, Malaria journal
BACKGROUND: The protection afforded by human erythrocyte polymorphisms against the malaria parasite, Plasmodium falciparum, has been proposed to be due to reduced ability of the parasite to invade or develop in erythrocytes. If this were the case, variable levels of parasitaemia and rates of seroconversion to infected-erythrocyte variant surface antigens (VSA) should be seen in different host genotypes. METHODS: To test this hypothesis, P. falciparum parasitaemia and anti-VSA antibody levels were measured in a cohort of 555 asymptomatic children from an area of intense malaria transmission in Papua New Guinea. Linear mixed models were used to investigate the effect of alpha+-thalassaemia, complement receptor-1 and south-east Asian ovalocytosis, as well as glucose-6-phosphate dehydrogenase deficiency and ABO blood group on parasitaemia and age-specific seroconversion to VSA. RESULTS: No host polymorphism showed a significant association with both parasite prevalence/density and age-specific seroconversion to VSA. CONCLUSION: Host erythrocyte polymorphisms commonly found in Papua New Guinea do not effect exposure to blood stage P. falciparum infection. This contrasts with data for sickle cell trait and highlights that the above-mentioned polymorphisms may confer protection against malaria via distinct mechanisms
— id: 78765, year: 2008, vol: 7, page: 1, stat: Journal Article,

Plasmodium-induced inflammation by uric acid
Orengo, Jamie M; Evans, James E; Bettiol, Esther; Leliwa-Sytek, Aleksandra; Day, Karen; Rodriguez, Ana
2008 Mar;4(3):e1000013-e1000013, PLoS pathogens
Infection of erythrocytes with the Plasmodium parasite causes the pathologies associated with malaria, which result in at least one million deaths annually. The rupture of infected erythrocytes triggers an inflammatory response, which is induced by parasite-derived factors that still are not fully characterized. Induced secretion of inflammatory cytokines by these factors is considered a major cause of malaria pathogenesis. In particular, the inflammatory cytokine tumor necrosis factor (TNF) is thought to mediate most of the life-threatening pathologies of the disease. Here we describe the molecular characterization of a novel pathway that results in the secretion of TNF by host cells. We found that erythrocytes infected by Plasmodium accumulate high concentrations of hypoxanthine and xanthine. Degradation of Plasmodium-derived hypoxanthine/xanthine results in the formation of uric acid, which triggers the secretion of TNF. Since uric acid is considered a 'danger signal' released by dying cells to alert the immune system, Plasmodium appears to have co-evolved to exploit this warning system. Identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease
— id: 78762, year: 2008, vol: 4, page: e1000013, stat: Journal Article,

Population genomics of the immune evasion (var) genes of Plasmodium falciparum
Barry, Alyssa E; Leliwa-Sytek, Aleksandra; Tavul, Livingston; Imrie, Heather; Migot-Nabias, Florence; Brown, Stuart M; McVean, Gilean A V; Day, Karen P
2007 Mar;3(3):e34-e34, PLoS pathogens
Var genes encode the major surface antigen (PfEMP1) of the blood stages of the human malaria parasite Plasmodium falciparum. Differential expression of up to 60 diverse var genes in each parasite genome underlies immune evasion. We compared the diversity of the DBLalpha domain of var genes sampled from 30 parasite isolates from a malaria endemic area of Papua New Guinea (PNG) and 59 from widespread geographic origins (global). Overall, we obtained over 8,000 quality-controlled DBLalpha sequences. Within our sampling frame, the global population had a total of 895 distinct DBLalpha 'types' and negligible overlap among repertoires. This indicated that var gene diversity on a global scale is so immense that many genomes would need to be sequenced to capture its true extent. In contrast, we found a much lower diversity in PNG of 185 DBLalpha types, with an average of approximately 7% overlap among repertoires. While we identify marked geographic structuring, nearly 40% of types identified in PNG were also found in samples from different countries showing a cosmopolitan distribution for much of the diversity. We also present evidence to suggest that recombination plays a key role in maintaining the unprecedented levels of polymorphism found in these immune evasion genes. This population genomic framework provides a cost effective molecular epidemiological tool to rapidly explore the geographic diversity of var genes
— id: 96299, year: 2007, vol: 3, page: e34, stat: Journal Article,

Change management and the sustainability of health ICT projects
Day, Karen; Norris, Tony
2007 ;12(Pt 2):1209-1213, Medinfo
The development of the electronic health record (EHR) is a strategic and important enabler of the delivery of integrated healthcare. As each innovative aspect of the EHR is implemented in New Zealand, long-term success is essential for its overall sustainability on the national scale. How we achieve this success is dependent upon how people adapt to the changes brought about by the implementation of these innovations. The transition period of the change process we follow during this adaptation is characterized by a capability crisis, in which we tend to predict failure in our attempts to make the changes to which we are committed. This could be a signal of the first step toward sustainable change as people adapt to changed processes, technology and relationships. Once we have mastered the incremental changes brought about by health ICT projects for the implementation of the EHR, we are able to connect health services by means of the same EHR and provide enabled, sustainable integrated healthcare
— id: 78767, year: 2007, vol: 12, page: 1209, stat: Journal Article,

alpha+-thalassaemia provides a haematological advantage against malaria
Fowkes, FJ; Allen, SJ; Allen, A; Alpers, MP; Weatherall, DJ; Day, KP
2007 NOV ;77(5):304-304, American journal of tropical medicine & hygiene
— id: 75813, year: 2007, vol: 77, page: 304, stat: Journal Article,

Susceptibility of Anopheles gambiae and Anopheles stephensi to tropical isolates of Plasmodium falciparum
Hume, Jennifer C C; Tunnicliff, Mark; Ranford-Cartwright, Lisa C; Day, Karen P
2007 ;6:139-139, Malaria journal
BACKGROUND: The susceptibility of anopheline mosquito species to Plasmodium infection is known to be variable with some mosquitoes more permissive to infection than others. Little work, however, has been carried out investigating the susceptibility of major malaria vectors to geographically diverse tropical isolates of Plasmodium falciparum aside from examining the possibility of infection extending its range from tropical regions into more temperate zones. METHODS: This study investigates the susceptibility of two major tropical mosquito hosts (Anopheles gambiae and Anopheles stephensi) to P. falciparum isolates of different tropical geographical origins. Cultured parasite isolates were fed via membrane feeders simultaneously to both mosquito species and the resulting mosquito infections were compared. RESULTS: Infection prevalence was variable with African parasites equally successful in both mosquito species, Thai parasites significantly more successful in An. stephensi, and PNG parasites largely unsuccessful in both species. CONCLUSION: Infection success of P. falciparum was variable according to geographical origin of both the parasite and the mosquito. Data presented raise the possibility that local adaptation of tropical parasites and mosquitoes has a role to play in limiting gene flow between allopatric parasite populations
— id: 78766, year: 2007, vol: 6, page: 139, stat: Journal Article,

LOW PREVALENCE OF AN ACUTE PHASE RESPONSE IN ASYMPTOMATIC CHILDREN FROM A MALARIA-ENDEMIC AREA OF PAPUA NEW GUINEA
Imrie, Heather; Fowkes, Freya J I; Michon, Pascal; Tavul, Livingstone; Reeder, John C; Day, Karen P
2007 Feb;76(2):280-284, American journal of tropical medicine & hygiene
Levels of C-reactive protein (CRP), a classic marker for the acute phase response (APR), were measured in children with asymptomatic malaria infection in the Amele region of Papua New Guinea (PNG). Despite the presence of parasitemia, the prevalence of CRP levels consistent with an APR (CRP > 10 mug/mL) was very low (< 10%). Splenomegaly was significantly associated with increased parasitemia (P < 0.001) and CRP levels (P < 0.001), highlighting the importance of splenomegaly as an indicator of recent high density infection in this population. Multivariate analysis showed that CRP levels were significantly associated with splenomegaly, fever, hemoglobin, and age (P </= 0.002). CRP levels also increased with increasing parasitemia (P < 0.001) but remained < 3.5 mug/mL. The low levels of CRP indicate that children in the Amele modulate inflammation associated with malaria
— id: 70774, year: 2007, vol: 76, page: 280, stat: Journal Article,

Molecular characterization of a Plasmodium-derived inflammatory factor
Orengo, JM; Evans, JE; Leliwa-Sytek, A; Day, KP; Rodriguez, A
2007 NOV ;77(5):185-186, American journal of tropical medicine & hygiene
— id: 75812, year: 2007, vol: 77, page: 185, stat: Journal Article,

Genomic heterogeneity in the density of noncoding single-nucleotide and microsatellite polymorphisms in Plasmodium falciparum
Volkman, Sarah K; Lozovsky, Elena; Barry, Alyssa E; Bedford, Trevor; Bethke, Lara; Myrick, Alissa; Day, Karen P; Hartl, Daniel L; Wirth, Dyann F; Sawyer, Stanley A
2007 Jan 31;387(1-2):1-6, Gene
The density and distribution of single-nucleotide polymorphisms (SNPs) across the genome has important implications for linkage disequilibrium mapping and association studies, and the level of simple-sequence microsatellite polymorphisms has important implications for the use of oligonucleotide hybridization methods to genotype SNPs. To assess the density of these types of polymorphisms in P. falciparum, we sampled introns and noncoding DNA upstream and downstream of coding regions among a variety of geographically diverse parasites. Across 36,229 base pairs of noncoding sequence representing 41 genetic loci, a total of 307 polymorphisms including 248 polymorphic microsatellites and 39 SNPs were identified. We found a significant excess of microsatellite polymorphisms having a repeat unit length of one or two, compared to those with longer repeat lengths, as well as a nonrandom distribution of SNP polymorphisms. Almost half of the SNPs localized to only three of the 41 genetic loci sampled. Furthermore, we find significant differences in the frequency of polymorphisms across the two chromosomes (2 and 3) examined most extensively, with an excess of SNPs and a surplus of polymorphic microsatellites on chromosome 3 as compared to chromosome 2 (P=0.0001). Furthermore, at some individual genetic loci we also find a nonrandom distribution of polymorphisms between coding and flanking noncoding sequences, where completely monomorphic regions may flank highly polymorphic genes. These data, combined with our previous findings of nonrandom distribution of SNPs across chromosome 2, suggest that the Plasmodium falciparum genome may be a mosaic with regard to genetic diversity, containing chromosomal regions that are highly polymorphic interspersed with regions that are much less polymorphic
— id: 78769, year: 2007, vol: 387, page: 1, stat: Journal Article,

Within-population variation in prevalence and lineage distribution of avian malaria in blue tits, Cyanistes caeruleus
Wood, Matthew J; Cosgrove, Catherine L; Wilkin, Teddy A; Knowles, Sarah C L; Day, Karen P; Sheldon, Ben C
2007 Aug;16(15):3263-3273, Molecular ecology
The development of molecular genetic screening techniques for avian blood parasites has revealed many novel aspects of their ecology, including greatly elevated diversity and complex host-parasite relationships. Many previous studies of malaria in birds have treated single study populations as spatially homogeneous with respect to the likelihood of transmission of malaria to hosts, and we have very little idea whether any spatial heterogeneity influences different malaria lineages similarly. Here, we report an analysis of variation in the prevalence and cytochrome b lineage distribution of avian malaria infection with respect to environmental and host factors, and their interactions, in a single blue tit (Cyanistes caeruleus) population. Of 11 Plasmodium and Haemoproteus cytochrome b lineages found in 997 breeding individuals, the three most numerous (pSGS1, pTURDUS1 and pBT7) were considered separately, in addition to analyses of all avian malaria lineages pooled. Our analyses revealed marked spatial differences in the prevalence and distribution of these lineages, with local prevalence of malaria within the population ranging from over 60% to less than 10%. In addition, we found several more complex patterns of prevalence with respect to local landscape features, host state, parasite genotype, and their interactions. We discuss the implications of such heterogeneity in parasite infection at a local scale for the study of the ecology and evolution of infectious diseases in natural populations. The increased resolution afforded by the combination of molecular genetic and geographical information systems (GIS) tools has the potential to provide many insights into the epidemiology, evolution and ecology of these parasites in the future
— id: 78768, year: 2007, vol: 16, page: 3263, stat: Journal Article,

Variable SNP density in aspartyl-protease genes of the malaria parasite Plasmodium falciparum
Barry, Alyssa E; Leliwa-Sytek, Aleksandra; Man, Kitty; Kasper, Jacob M; Hartl, Daniel L; Day, Karen P
2006 Jul 19;376(2):163-173, Gene
An analysis of the diversity of the aspartyl proteases of Plasmodium falciparum, known as plasmepsins (PMs), was completed in view of their possible role as drug targets. DNA sequence polymorphisms were identified in nine pm genes including their non-coding (introns and 5' flanking) sequences. All genes contained at least one single nucleotide polymorphism (SNP). Extensive microsatellite diversity was observed predominantly in non-coding sequences. All but one non-synonymous polymorphism (a conservative substitution) were mapped to the surface of the predicted protein, contradicting a possible role in enzymatic activity. The distribution of SNPs was found to be non-random among pm genes, with pm6 and pm10 having significantly higher SNP densities, suggesting they were under selection. For pm6 the majority of the SNPs were in introns and some of these may contribute to splice site variation. SNPs were found at a high density in both the coding and non-coding sequences of pm10. Recombination was important in generating additional diversity at this locus. Although direct selection for pm10 mutations could not be ruled out, the presence of balancing selection and a high density of SNPs in non-coding sequence led us to propose that another gene under selection may be influencing the diversity in the region. By sequencing short DNA tags in a 200 kb region flanking pm10 we show that a cluster of antigen genes, known to be under diversifying selection, may contribute to the observed diversity. We discuss the importance of diversity and local selection effects when choosing drug targets for intervention strategies
— id: 78770, year: 2006, vol: 376, page: 163, stat: Journal Article,

No evidence for avian malaria infection during the nestling phase in a passerine bird
Cosgrove, Catherine L; Knowles, Sarah C L; Day, Karen P; Sheldon, Ben C
2006 Dec;92(6):1302-1304, Journal of parasitology
One of many uncertainties concerning the epidemiology of avian malaria in wild bird populations is the age at first infection. While nestlings, being naked and presumably immunologically naive would seem a likely stage of first infection, most age-stratified prevalence studies have not examined the nestling cohort, whereas those that have use relatively insensitive blood smear examination to diagnose infection. In the study presented here, we used sensitive nested polymerase chain reaction methods to screen blood samples from 195, 14-day-old blue tit (Cyanistes caeruleus) nestlings for avian malaria parasites (species of Plasmodium and Haemoproteus). Adults in this population are commonly infected with Plasmodium spp. (prevalence c. 30%). No avian malaria infections were found in nestlings, but a single positive identification of the related hematozoan parasite, Leucocytozoon sp., was made. Our results suggest either that the nestlings were infected but the disease had not yet reached patency, or that young birds in the nest are not bitten by the insect vectors of the disease
— id: 70775, year: 2006, vol: 92, page: 1302, stat: Journal Article,

Coamplification of Leucocytozoon by PCR diagnostic tests for avian malaria: A cautionary note
Cosgrove, CL; Day, KP; Sheldon, BC
2006 DEC ;92(6):1362-1365, Journal of parasitology
A number of PCR assays have now been described for detecting species of the avian malaria parasites Plasinodium and Haemoproteus from blood samples. The published protocols amplify both genera simultaneously, owing to the high degree of sequence similarity between them in target genes. However, the potential for coamplification in these assays of a third, closely related hematozoan parasite, Leucocytozoon spp. has been largely overlooked. In this paper, we highlight the importance of this issue, showing that coamplification of Leucocytozoon spp. occurs in several of the protocols designed to amplify avian malaria parasites. This leads not only to scoring of false positives but, in cases of mixed Leucocytozoon/malaria infections, may also lead to scoring of false negatives. We, therefore, advocate the use of a post-PCR diagnostic step, such as RFLP analysis or sequencing, to assess the contribution of Leucocytozoon spp. to overall prevalence
— id: 70750, year: 2006, vol: 92, page: 1362, stat: Journal Article,

Association of haptoglobin levels with age, parasite density, and haptoglobin genotype in a malaria-endemic area of Gabon
Fowkes, Freya J I; Imrie, Heather; Migot-Nabias, Florence; Michon, Pascal; Justice, Anita; Deloron, Phillipe; Luty, Adrian J F; Day, Karen P
2006 Jan;74(1):26-30, American journal of tropical medicine & hygiene
Haptoglobin (Hp) levels were investigated in relation to host genotype in a malaria-endemic area in Gabon. A cross-sectional study of 1-12-year-old children was conducted in the rainy season, a period of high malaria transmission, to examine this relationship. Variables that influenced Hp levels were Hp genotype, location, and age interacting with parasite density. At low parasite densities, there was a negative correlation between Hp levels and age. At higher densities, there was a positive correlation with age. This suggests that in the presence of greater parasite-induced hemolysis, older children are capable of increased production of Hp. Sickle cell trait and ABO blood group was not associated with Hp levels in this population
— id: 78771, year: 2006, vol: 74, page: 26, stat: Journal Article,

Haptoglobin levels are associated with haptoglobin genotype and alpha+ -Thalassemia in a malaria-endemic area
Imrie, Heather; Fowkes, Freya J I; Michon, Pascal; Tavul, Livingstone; Hume, Jennifer C C; Piper, Karen P; Reeder, John C; Day, Karen P
2006 Jun;74(6):965-971, American journal of tropical medicine & hygiene
Haptoglobin (Hp) is an acute phase protein that removes free hemoglobin (Hb) released during hemolysis. Hp has also been shown to be toxic for malaria parasites. alpha(+)-Thalassemia is a hemoglobinopathy that results in subclinical hemolytic anemia. alpha(+)-Thassemia homozygosity confers protection against severe malarial disease by an as yet unidentified mechanism. Hp levels were measured in a serial cross-sectional survey of children in Madang Province, Papua New Guinea (PNG). Hp levels were related to age, Hp genotype, Hb levels, parasitemia, splenomegaly, and alpha(+)-thalassemia genotype. Surprisingly, children who were homozygous for alpha(+) -thalassemia had significantly higher levels of Hp than did heterozygotes, after controlling for relevant confounders. We suggest that this is the result of either reduced mean cell Hb associated with alpha(+) -thalassemia homozygosity or an elevated IL-6-dependent acute phase response
— id: 70779, year: 2006, vol: 74, page: 965, stat: Journal Article,

Human serum haptoglobin is toxic to Plasmodium falciparum in vitro
Imrie, Heather; Ferguson, David J P; Day, Karen P
2004 Jan;133(1):93-98, Molecular & biochemical parasitology
Innate immune responses are important in the control of malaria, particularly in those who have not yet mounted an effective adaptive response. Here we report that the human serum acute phase protein, haptoglobin, is toxic to Plasmodium falciparum cultured in vitro. This effect is phenotype dependent and occurs during the trophozoite phase of the asexual life cycle. We propose that the increased levels of haptoglobin seen in the acute phase response may be protective against malaria in humans
— id: 40109, year: 2004, vol: 133, page: 93, stat: Journal Article,

DNA sequence artifacts and the estimation of time to the most recent common ancestor (TMRCA) of Plasmodium falciparum
Barry, Alyssa E; Leliwa, Aleksandra; Choi, Mehee; Nielsen, Kaare M; Hartl, Daniel L; Day, Karen P
2003 Aug 31;130(2):143-147, Molecular & biochemical parasitology
— id: 40110, year: 2003, vol: 130, page: 143, stat: Journal Article,

Cross-species regulation of Plasmodium parasitemia in semi-immune children from Papua New Guinea
Bruce, Marian C; Day, Karen P
2003 Jun;19(6):271-277, Trends in parasitology
Malariologists have long been fascinated by the question of whether Plasmodium spp. interact in the human host. The first genetic study of the longitudinal dynamics of multiple Plasmodium spp. and genotypes in humans has been completed in Papua New Guinea, where all four Plasmodium spp. that infect humans are present. The broad implications of the data from this study are covered here and they show that the total parasite density of Plasmodium species oscillates around a threshold and that peaks of infection with each species do not coincide. It is proposed that malaria parasitemia is controlled in a density-dependent manner in these semi-immune children and that a cross-species mechanism of parasite regulation exists. A model of how multiple immune responses could act in concert to explain these within-host dynamics are discussed here in relation to observed epidemiological patterns of mixed-species infections
— id: 40112, year: 2003, vol: 19, page: 271, stat: Journal Article,

Regulation of the rate of asexual growth and commitment to sexual development by diffusible factors from in vitro cultures of Plasmodium falciparum
Dyer, Mike; Day, Karen P
2003 Apr;68(4):403-409, American journal of tropical medicine & hygiene
The mechanism of switching to sexual differentiation (gametocytogenesis) of Plasmodium falciparum appears to be controlled by stochastic mechanisms that are sensitive to environmental conditions. In any given conditions, only a proportion of genetically identical parasites will become committed to sexual development. We used an experimental co-culture system to detect the presence of diffusible molecules from asexually replicating bloodstream stages of P. falciparum that were capable of influencing the growth and differentiation of the parasite. We cultured two populations of P. falciparum in a shared environment separated by a membrane that allowed free diffusion of molecules. The data presented show that P. falciparum parasites in culture stimulate their own growth and replication, and constitutively inhibit sexual conversion via diffusible molecules. These observations support the model that for P. falciparum, the sexual pathway of development is the default, and that constitutive repression of the sexual pathway permits asexual multiplication to occur in the bloodstream of the human host
— id: 40111, year: 2003, vol: 68, page: 403, stat: Journal Article,

The antiquity of malaria infection in humans : a genetics perspective
Hume J; Lyons E; Day KP
2003 ;35(2):180-192, World archaeology
— id: 70810, year: 2003, vol: 35, page: 180, stat: Journal Article,

Human migration, mosquitoes and the evolution of Plasmodium falciparum
Hume, Jennifer C C; Lyons, Emily J; Day, Karen P
2003 Mar;19(3):144-149, Trends in parasitology
To date, coalescent analysis of the Plasmodium falciparum genome sequence has failed to provide a unifying theory regarding the parasite's evolution. While a better understanding of the evolution of the malaria genome will undoubtedly clarify the current controversy, the importance of the parasite's interplay with both the human host and mosquito vector cannot be underestimated. Changes in the population biology or ecology of either one of these species have consequences for malaria transmission and this was never more apparent than in the environmental changes brought about by the advent of agriculture
— id: 40113, year: 2003, vol: 19, page: 144, stat: Journal Article,

Cross-species regulation of malaria parasitaemia in the human host
Bruce, Marian C; Day, Karen P
2002 Aug;5(4):431-437, Current opinion in microbiology
Longitudinal genetic analysis of the composition of malaria parasites infecting humans has demonstrated that individuals living in endemic areas are chronically infected with multiple genotypes and species of Plasmodium. The accumulation of infections is a consequence of superinfection from the bites of many infected anopheline mosquitoes. The clinical outcome of infection is determined by the host's ability to regulate the density of malaria parasites in the blood. Interestingly, most infections do not cause symptoms of malarial disease after a degree of immunity is acquired. Here, we review data from the first genetic study of the longitudinal dynamics of multiple Plasmodium species and genotypes in humans. The data show that the total parasite density of Plasmodium species oscillates around a threshold and that peaks of infection with each species do not coincide. We propose that malaria parasitaemia is controlled in a density-dependent manner in these semi-immune children. This implies that a cross-species mechanism of parasite regulation exists. A model of how multiple immune responses could act in concert to explain these within host dynamics is discussed in relation to known regulatory mechanisms
— id: 40114, year: 2002, vol: 5, page: 431, stat: Journal Article,

The paradoxical population genetics of Plasmodium falciparum
Hartl, Daniel L; Volkman, Sarah K; Nielsen, Kaare M; Barry, Alyssa E; Day, Karen P; Wirth, Dyann F; Winzeler, Elizabeth A
2002 Jun;18(6):266-272, Trends in parasitology
Among the leading causes of death in African children is cerebral malaria caused by the parasitic protozoan Plasmodium falciparum. Endemic forms of this disease are thought to have originated in central Africa 5000-10000 years ago, coincident with the innovation of slash-and-burn agriculture and the diversification of the Anopheles gambiae complex of mosquito vectors. Population genetic studies of P. falciparum have yielded conflicting results. Some evidence suggests that today's population includes multiple ancient lineages pre-dating human speciation. Other evidence suggests that today's population derives from only one, or a small number, of these ancient lineages. Resolution of this issue is important for the evaluation of the long-term efficacy of drug and immunological control strategies
— id: 40115, year: 2002, vol: 18, page: 266, stat: Journal Article,

Genotyping of Plasmodium falciparum infections by PCR: a comparative multicentre study
Farnert A; Arez AP; Babiker HA; Beck HP; Benito A; Bjorkman A; Bruce MC; Conway DJ; Day KP; Henning L; Mercereau-Puijalon O; Ranford-Cartwright LC; Rubio JM; Snounou G; Walliker D; Zwetyenga J; do Rosario VE
2001 Mar-Apr;95(2):225-232, Transactions of the Royal Society of Tropical Medicine & Hygiene
Genetic diversity of malaria parasites represents a major issue in understanding several aspects of malaria infection and disease. Genotyping of Plasmodium falciparum infections with polymerase chain reaction (PCR)-based methods has therefore been introduced in epidemiological studies. Polymorphic regions of the msp1, msp2 and glurp genes are the most frequently used markers for genotyping, but methods may differ. A multicentre study was therefore conducted to evaluate the comparability of results from different laboratories when the same samples were analysed. Analyses of laboratory-cloned lines revealed high specificity but varying sensitivity. Detection of low-density clones was hampered in multiclonal infections. Analyses of isolates from Tanzania and Papua New Guinea revealed similar positivity rates with the same allelic types identified. The number of alleles detected per isolate, however, varied systematically between the laboratories especially at high parasite densities. When the analyses were repeated within the laboratories, high agreement was found in getting positive or negative results but with a random variation in the number of alleles detected. The msp2 locus appeared to be the most informative single marker for analyses of multiplicity of infection. Genotyping by PCR is a powerful tool for studies on genetic diversity of P. falciparum but this study has revealed limitations in comparing results on multiplicity of infection derived from different laboratories and emphasizes the need for highly standardized laboratory protocols
— id: 40118, year: 2001, vol: 95, page: 225, stat: Journal Article,

Epitopes for modified band 3 monoclonal antibody 1C4 are not exposed on the malaria-infected red blood cell surface
Hayward RE; Day KP
2001 Oct;117(2):235-239, Molecular & biochemical parasitology
— id: 40116, year: 2001, vol: 117, page: 235, stat: Journal Article,

Recent origin of Plasmodium falciparum from a single progenitor
Volkman SK; Barry AE; Lyons EJ; Nielsen KM; Thomas SM; Choi M; Thakore SS; Day KP; Wirth DF; Hartl DL
2001 Jul 20;293(5529):482-484, Science
Genetic variability of Plasmodium falciparum underlies its transmission success and thwarts efforts to control disease caused by this parasite. Genetic variation in antigenic, drug resistance, and pathogenesis determinants is abundant, consistent with an ancient origin of P. falciparum, whereas DNA variation at silent (synonymous) sites in coding sequences appears virtually absent, consistent with a recent origin of the parasite. To resolve this paradox, we analyzed introns and demonstrated that these are deficient in single-nucleotide polymorphisms, as are synonymous sites in coding regions. These data establish the recent origin of P. falciparum and further provide an explanation for the abundant diversity observed in antigen and other selected genes
— id: 40117, year: 2001, vol: 293, page: 482, stat: Journal Article,

Geographical structure and sequence evolution as inferred from the Plasmodium falciparum S-antigen locus
Anderson TJ; Day KP
2000 Mar 5;106(2):321-326, Molecular & biochemical parasitology
— id: 40126, year: 2000, vol: 106, page: 321, stat: Journal Article,

Microsatellite markers reveal a spectrum of population structures in the malaria parasite Plasmodium falciparum
Anderson TJ; Haubold B; Williams JT; Estrada-Franco JG; Richardson L; Mollinedo R; Bockarie M; Mokili J; Mharakurwa S; French N; Whitworth J; Velez ID; Brockman AH; Nosten F; Ferreira MU; Day KP
2000 Oct;17(10):1467-1482, Molecular biology & evolution
Multilocus genotyping of microbial pathogens has revealed a range of population structures, with some bacteria showing extensive recombination and others showing almost complete clonality. The population structure of the protozoan parasite Plasmodium falciparum has been harder to evaluate, since most studies have used a limited number of antigen-encoding loci that are known to be under strong selection. We describe length variation at 12 microsatellite loci in 465 infections collected from 9 locations worldwide. These data reveal dramatic differences in parasite population structure in different locations. Strong linkage disequilibrium (LD) was observed in six of nine populations. Significant LD occurred in all locations with prevalence <1% and in only two of five of the populations from regions with higher transmission intensities. Where present, LD results largely from the presence of identical multilocus genotypes within populations, suggesting high levels of self-fertilization in populations with low levels of transmission. We also observed dramatic variation in diversity and geographical differentiation in different regions. Mean heterozygosities in South American countries (0.3-0.4) were less than half those observed in African locations (0. 76-0.8), with intermediate heterozygosities in the Southeast Asia/Pacific samples (0.51-0.65). Furthermore, variation was distributed among locations in South America (F:(ST) = 0.364) and within locations in Africa (F:(ST) = 0.007). The intraspecific patterns of diversity and genetic differentiation observed in P. falciparum are strikingly similar to those seen in interspecific comparisons of plants and animals with differing levels of outcrossing, suggesting that similar processes may be involved. The differences observed may also reflect the recent colonization of non-African populations from an African source, and the relative influences of epidemiology and population history are difficult to disentangle. These data reveal a range of population structures within a single pathogen species and suggest intimate links between patterns of epidemiology and genetic structure in this organism
— id: 40123, year: 2000, vol: 17, page: 1467, stat: Journal Article,

Do malaria parasites mate non-randomly in the mosquito midgut?
Anderson TJ; Paul RE; Donnelly CA; Day KP
2000 Jun;75(3):285-296, Genetical research
Polymerase chain reaction (PCR)-based genotyping of oocysts dissected from mosquito midguts has previously been used to investigate overall levels of inbreeding within malaria parasite populations. We present a re-analysis of the population structure of Plasmodium falciparum malaria using diploid genotypes at three antigen-encoding loci in 118 oocysts dissected from 34 mosquitoes. We use these data to ask whether mating is occurring at random within the mosquito midgut, as is generally assumed. We observe a highly significant deficit of heterozygous oocysts within mosquitoes at all three loci, suggesting that fusion of gametes occurs non-randomly in the mosquito gut. A variety of biological explanations, such as interrupted feeding of mosquitoes, positive assortative mating and outcrossing depression, could account for this observation. However, an alternative artefactual explanation--the presence of non-amplifying or null alleles--can account for the observed data equally well, without the need to invoke non-random mating. To evaluate this explanation further, we estimate the frequencies of null alleles within the oocyst population using maximum likelihood, by making the assumption that non-amplifying oocysts at any of the three loci are homozygous for null alleles. Observed levels of visible heterozygotes fit closely with those expected under random mating when non-amplifying oocysts are accounted for. Other lines of evidence also support the artefactual explanation. Overall inbreeding coefficients have been recalculated in the light of this analysis, and may be considerably lower than those estimated previously. In conclusion, we suggest that the deficit of heterozygotes observed is unlikely to indicate non-random mating within the mosquito gut and is better explained by misscoring of heterozygotes as homozygotes
— id: 40124, year: 2000, vol: 75, page: 285, stat: Journal Article,

Complex mutations in a high proportion of microsatellite loci from the protozoan parasite Plasmodium falciparum
Anderson TJ; Su XZ; Roddam A; Day KP
2000 Oct;9(10):1599-1608, Molecular ecology
Microsatellite loci are generally assumed to evolve via a stepwise mutational process and a battery of statistical techniques has been developed in recent years based on this or related mutation models. It is therefore important to investigate the appropriateness of these models in a wide variety of taxa. We used two approaches to examine mutation patterns in the malaria parasite Plasmodium falciparum: (i) we examined sequence variation at 12 tri-nucleotide repeat loci; and (ii) we analysed patterns of repeat structure and heterozygosity at 114 loci using data from 12 laboratory parasite lines. The sequencing study revealed complex patterns of mutation in five of the 12 loci studied. Alleles at two loci contain indels of 24 bp and 57 bp in flanking regions, while in the other three loci, blocks of imperfect microsatellites appear to be duplicated or inserted; these loci essentially consist of minisatellite repeats, with each repeat unit containing four to eight microsatellites. The survey of heterozygosity revealed a positive relationship between repeat number and microsatellite variability for both di- and trinucleotides, indicating a higher mutation rate in loci with longer repeat arrays. Comparisons of levels of variation in different repeat types indicate that the mutation rate of dinucleotide-bearing loci is 1.6-2.1 times faster than trinucleotides, consistent with the lower mean number of repeats in trinucleotide-bearing loci. However, despite the evidence that microsatellite arrays themselves are evolving in a manner consistent with stepwise mutation model in P. falciparum, the high frequency of complex mutations precludes the use of analytical tools based on this mutation model for many microsatellite-bearing loci in this protozoan. The results call into question the generality of models based on stepwise mutation for analysing microsatellite data, but also demonstrate the ease with which loci that violate model assumptions can be detected using minimal sequencing effort
— id: 40122, year: 2000, vol: 9, page: 1599, stat: Journal Article,

Cross-species interactions between malaria parasites in humans
Bruce MC; Donnelly CA; Alpers MP; Galinski MR; Barnwell JW; Walliker D; Day KP
2000 Feb 4;287(5454):845-848, Science
The dynamics of multiple Plasmodium infections in asymptomatic children living under intense malaria transmission pressure provide evidence for a density-dependent regulation that transcends species as well as genotype. This regulation, in combination with species- and genotype-specific immune responses, results in nonindependent, sequential episodes of infection with each species
— id: 40128, year: 2000, vol: 287, page: 845, stat: Journal Article,

Age- and species-specific duration of infection in asymptomatic malaria infections in Papua New Guinea
Bruce MC; Donnelly CA; Packer M; Lagog M; Gibson N; Narara A; Walliker D; Alpers MP; Day KP
2000 Sep;121 ( Pt 3)(3):247-256, Parasitology
The burden and duration of asymptomatic malaria infections were measured in residents of the malaria endemic village of Gonoa, Madang Province, Papua New Guinea. Plasmodium falciparum, P. vivax and P. malariae infections in people aged 4 years to adulthood were compared. Frequent sampling at 3-day intervals for up to 61 days allowed assessment of individual episodes of infection. Statistical assessment of P. falciparum detection revealed a periodicity consistent with synchronous replication of this species over periods up to 27 days. The duration of P. falciparum episodes was longer across all age groups than that of P. vivax and P. malariae. A trend for decreasing duration with age was also noted in data from each species. This was most prominent in P. falciparum infections: median duration in 4-year-olds was > 48 days compared with a median between 9 and 15 days in older children and adults. The results are consistent with the slow acquisition of immunity to antigenically diverse Plasmodium populations and suggest a faster rate of acquisition to P. vivax and P. malariae than to P. falciparum
— id: 40121, year: 2000, vol: 121 ( Pt 3), page: 247, stat: Journal Article,

Genetic diversity and dynamics of plasmodium falciparum and P. vivax populations in multiply infected children with asymptomatic malaria infections in Papua New Guinea
Bruce MC; Galinski MR; Barnwell JW; Donnelly CA; Walmsley M; Alpers MP; Walliker D; Day KP
2000 Sep;121 ( Pt 3)(3):257-272, Parasitology
We describe the dynamics of co-infections of Plasmodium falciparum and P. vivax in 28 asymptomatic children by genotyping these species using the polymorphic loci Msp2 and Msp3alpha, respectively. The total number of Plasmodium spp. infections detected using 3 day sampling over 61 days varied between 1 and 14 (mean 6.6). The dynamics of P. falciparum and P. vivax genotypes varied greatly both within and amongst children. Periodicity in the detection of P. falciparum infections is consistent with the synchronous replication of individual genotypes. Replication synchrony of multiple co-infecting genotypes was not detected. In 4-year-old children P. falciparum genotype complexity was reduced and episodes lasted significantly longer (median duration > 60 days) when compared to children aged 5-14 years (median duration 9 days). P. vivax genotype complexity was not correlated with age but the episode duration was also longer for this species in 4-year-olds than in older children but was not as long as P. falciparum episodes. Recurrence of P. falciparum and P. vivax genotypes over weeks was observed. We interpret these major fluctuations in the density of genotypes over time as the result of the mechanism of antigenic variation thought to be present in these Plasmodium species
— id: 40120, year: 2000, vol: 121 ( Pt 3), page: 257, stat: Journal Article,

Erratum to "Expression of Plasmodium falciparum trimeric G proteins and their involvement in switching to sexual development"
Dyer M; Day K
2000 Oct 1;110(2):435-435, Molecular & biochemical parasitology
— id: 70776, year: 2000, vol: 110, page: 435, stat: Journal Article,

Commitment to gametocytogenesis in Plasmodium falciparum
Dyer M; Day KP
2000 Mar;16(3):102-107, Parasitology today
To achieve transmission, a subpopulation of asexually dividing bloodstream forms of the human malaria parasite Plasmodium falciparum withdraws from the cell cycle to develop into gametocytes - cells specialized for sexual reproduction and invasion of the mosquito vector. For natural selection to maximize transmission to new hosts, a balance must have evolved between asexual replication and sexual differentiation. Here, Mike Dyer and Karen Day consider observations on the process of commitment to gametocytogenesis and use this information as the framework for a model that begins to explain the control of the dynamics between asexual and sexual development
— id: 40127, year: 2000, vol: 16, page: 102, stat: Journal Article,

Expression of Plasmodium falciparum trimeric G proteins and their involvement in switching to sexual development
Dyer, M; Day, K
2000 Apr 30;108(1):67-78, Molecular & biochemical parasitology
Both cholera and pertussis toxins were used to label and study the expression of heterotrimeric G protein alpha subunits in Plasmodium falciparum extracts. Expression of these proteins is developmentally regulated throughout the erythrocytic cycle with peak expression during early asexual development and in mature sexual stages. Treatment of P. falciparum cultures with cholera toxin causes an increase in conversion to sexual development, and at the same concentration has a marginal inhibitory effect on asexual growth and division. Through precise synchronisation of the parasites' asexual cell cycle, we have defined the period of sensitivity to this induction at around the time of invasion, one cycle before the development of the sexual form. Fluorescent microscopy confirmed that access of the toxin to the parasite is limited to the invasive form - the free merozoite, while further labelling studies revealed expression of a single G protein alpha subunit in these stages. These observations are consistent with the view that a G protein-dependent signal transduction pathway is involved in coupling the parasite's environment to commitment to sexual development (gametocytogenesis). This means of artificially stimulating the pathways leading to sexual development can now be used to biochemically follow the activation of the signalling pathways involved
— id: 70778, year: 2000, vol: 108, page: 67, stat: Journal Article,

Expression of Plasmodium falciparum trimeric G proteins and their involvement in switching to sexual development
Dyer, M; Day, K
2000 Oct;110(2):437-448, Molecular & biochemical parasitology
Both cholera and pertussis toxins were used to label and study the expression of heterotrimeric G protein alpha subunits in Plasmodium falciparum extracts. Expression of these proteins is developmentally regulated throughout the erythrocytic cycle with peak expression during early asexual development and in mature sexual stages. Treatment of P. falciparum cultures with cholera toxin causes an increase in conversion to sexual development, and at the same concentration has a marginal inhibitory effect on asexual growth and division. Through precise synchronisation of the parasites' asexual cell cycle, we have defined the period of sensitivity to this induction at around the time of invasion, one cycle before the development of the sexual form. Fluorescent microscopy confirmed that access of the toxin to the parasite is limited to the invasive form--the free merozoite, while further labelling studies revealed expression of a single G protein alpha subunit in these stages. These observations are consistent with the view that a G protein-dependent signal transduction pathway is involved in coupling the parasite's environment to commitment to sexual development (gametocytogenesis). This means of artificially stimulating the pathways leading to sexual development can now be used to biochemically follow the activation of the signalling pathways involved
— id: 70777, year: 2000, vol: 110, page: 437, stat: Journal Article,

Plasmodium falciparum: histidine-rich protein II is expressed during gametocyte development
Hayward RE; Sullivan DJ; Day KP
2000 Nov;96(3):139-146, Experimental parasitology
Both early gametocytes (I-II) and asexual trophozoite stages of Plasmodium falciparum digest hemoglobin and detoxify haem by polymerizing it into parasite pigment called hemozoin. The mechanism of polymerization is unclear but it has been proposed that histidine-rich protein II may facilitate transport of hemoglobin to the food vacuole and catalyze the polymerization in asexual stages. We describe the transcription of histidine-rich protein II in gametocytes by Northern blot analysis and the expression of the protein in these stages by immunoprecipitation and Western blotting. Localization of histidine-rich protein II within the gametocyte by immunofluorescence assay and immunoelectron microscopy clearly illustrated the presence of this molecule in the infected red cell cytosol in the early stages of gametocyte development and internalization in the later gametocyte as it matures. There is a strong correlation between the stage-specific trafficking of histidine-rich protein II in gametocytes and the susceptibility of early but not late gametocytes to the antimalarial drug chloroquine
— id: 40119, year: 2000, vol: 96, page: 139, stat: Journal Article,

Twelve microsatellite markers for characterization of Plasmodium falciparum from finger-prick blood samples
Anderson TJ; Su XZ; Bockarie M; Lagog M; Day KP
1999 Aug;119 ( Pt 2)(4):113-125, Parasitology
Multiple, selectively neutral genetic markers are the most appropriate tools for analysis of parasite population structure and epidemiology, but yet existing methods for characterization of malaria field samples utilize a limited number of antigen encoding genes, which appear to be under strong selection. We describe protocols for characterization of 12 microsatellite markers from finger-prick blood samples infected with Plasmodium falciparum. A two-step, heminested strategy was used to amplify all loci, and products were visualized by fluorescent end-labelling of internal primers. This procedure allows amplification from low levels of template, while eliminating the problem of spurious products due to primer carry over from the primary round of PCR. The loci can be conveniently multiplexed, while accurate sizing and quantification of PCR products can be automated using the GENOTYPER software. The primers do not amplify co-infecting malaria species such as P. vivax and P. malariae. To demonstrate the utility of these markers, we characterized 57 infected finger-prick blood samples from the village of Mebat in Papua New Guinea for all 12 loci, and all samples were genotyped a second time to measure reproducibility. Numbers of alleles per locus range from 4 to 10 in this population, while heterozygosities range from 0.21 to 0.87. Reproducibility (measured as concordance between predominant alleles detected in replicate samples) ranged from 92 to 98% for the 12 loci. The composition of PCR products from infections containing multiple malaria clones could also be defined using strict criteria and scored in a highly repeatable manner
— id: 40131, year: 1999, vol: 119 ( Pt 2), page: 113, stat: Journal Article,

Application of genetic markers to the identification of recrudescent Plasmodium falciparum infections on the northwestern border of Thailand
Brockman A; Paul RE; Anderson TJ; Hackford I; Phaiphun L; Looareesuwan S; Nosten F; Day KP
1999 Jan;60(1):14-21, American journal of tropical medicine & hygiene
Parasite genotyping by the polymerase chain reaction was used to distinguish recrudescent from newly acquired Plasmodium falciparum infections in a Karen population resident on the northwestern border of Thailand where malaria transmission is low (one infection/person/year). Plasmodium falciparum infections were genotyped for allelic variation in three polymorphic antigen loci, merozoite surface proteins-1 and -2 (MSP-1 and -2) and glutamaterich protein (GLURP), before and after antimalarial drug treatment. Population genotype frequencies were measured to provide the baseline information to calculate the probability of a new infection with a different or the same genotype to the initial pretreatment isolate. Overall, 38% of the infections detected following treatment had an identical genotype before and up to 121 days after treatment. These post-treatment genotypes were considered recrudescent because of the low (< 5%) probability of repeated occurrence by chance in the same patient. This approach allows studies of antimalarial drug treatment to be conducted in areas of low transmission since recrudescences can be distinguished confidently from newly acquired infections
— id: 40134, year: 1999, vol: 60, page: 14, stat: Journal Article,

Polymorphism at the merozoite surface protein-3alpha locus of Plasmodium vivax: global and local diversity
Bruce MC; Galinski MR; Barnwell JW; Snounou G; Day KP
1999 Oct;61(4):518-525, American journal of tropical medicine & hygiene
Allelic diversity at the Plasmodium vivax merozoite surface protein-3alpha (PvMsp-3alpha) locus was investigated using a combined polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) protocol. Symptomatic patient isolates from global geographic origins showed a high level of polymorphism at the nucleotide level. These samples were used to validate the sensitivity, specificity, and reproducibility of the PCR/RFLP method. It was then used to investigate PvMsp3alpha diversity in field samples from children living in a single village in a malaria-endemic region of Papua New Guinea, with the aim of assessing the usefulness of this locus as an epidemiologic marker of P. vivax infections. Eleven PvMsp-3alpha alleles were distinguishable in 16 samples with single infections, revealing extensive parasite polymorphism within this restricted area. Multiple infections were easily detected and accounted for 5 (23%) of 22 positive samples. Pairs of samples from individual children provided preliminary evidence for high turnover of P. vivax populations
— id: 40130, year: 1999, vol: 61, page: 518, stat: Journal Article,

Parasite genetics and the epidemiology of malaria
Day KP
Malaria : molecular and clinical aspects Amsterdam : Harwood Academic, 1999,
— id: 4232, year: 1999, vol: , page: 57, stat: Chapter,

Virulence and transmission success of the malarial parasite Plasmodium falciparum
Hayward RE; Tiwari B; Piper KP; Baruch DI; Day KP
1999 Apr 13;96(8):4563-4568, Proceedings of the National Academy of Sciences of the United States of America
Virulence of Plasmodium falciparum is associated with the expression of variant surface antigens designated PfEMP1 (P. falciparum erythrocyte membrane protein 1) that are encoded by a family of var genes. Data presented show that the transmission stages of P. falciparum also express PfEMP1 variants. Virulence in this host-parasite system can be considered a variable outcome of optimizing the production of sexual transmission stages from the population of disease-inducing asexual stages. Immunity to PfEMP1 will contribute to the regulation of this trade-off by controlling the parasite population with potential to produce mature transmission stages
— id: 40132, year: 1999, vol: 96, page: 4563, stat: Journal Article,

Aggregation and distribution of strains in microparasites
Lord, C C; Barnard, B; Day, K; Hargrove, J W; McNamara, J J; Paul, R E; Trenholme, K; Woolhouse, M E
1999 Apr 29;354(1384):799-807, Philosophical transactions of the Royal Society of London. Series B. Biological sciences
Recent research has shown that many parasite populations are made up of a number of epidemiologically distinct strains or genotypes. The implications of strain structure or genetic diversity for parasite population dynamics are still uncertain, partly because there is no coherent framework for the interpretation of field data. Here, we present an analysis of four published data sets for vector-borne microparasite infections where strains or genotypes have been distinguished: serotypes of African horse sickness (AHS) in zebra; types of Nannomonas trypanosomes in tsetse flies; parasite-induced erythrocyte surface antigen (PIESA) based isolates of Plasmodium falciparum malaria in humans, and the merozoite surface protein 2 gene (MSP-2) alleles of P. falciparum in humans and in anopheline mosquitoes. For each data set we consider the distribution of strains or types among hosts and any pairwise associations between strains or types. Where host age data are available we also compare age-prevalence relationships and estimates of the force of infection. Multiple infections of hosts are common and for most data sets infections have an aggregated distribution among hosts with a tendency towards positive associations between certain strains or types. These patterns could result from interactions (facilitation) between strains or types, or they could reflect patterns of contact between hosts and vectors. We use a mathematical model to illustrate the impact of host-vector contact patterns, finding that even if contact is random there may still be significant aggregation in parasite distributions. This effect is enhanced if there is non-random contact or other heterogeneities between hosts, vectors or parasites. In practice, different strains or types also have different forces of infection. We anticipate that aggregated distributions and positive associations between microparasite strains or types will be extremely common
— id: 70780, year: 1999, vol: 354, page: 799, stat: Journal Article,

Genetic analysis of Plasmodium falciparum infections on the north-western border of Thailand
Paul RE; Brockman A; Price RN; Luxemburger C; White NJ; Looareesuwan S; Nosten F; Day KP
1999 Nov-Dec;93(6):587-593, Transactions of the Royal Society of Tropical Medicine & Hygiene
Genetic characterization of Plasmodium falciparum infections in north-western Thailand, a region of low transmission intensity (1 infection/person each year), has found a comparable number of parasite genotypes per infected person to regions with hyperendemic malaria. Clone multiplicity and parasite diversity were found to be homogeneous across 129 infected individuals comprising a range of age-groups (1.32 parasite genotypes; n = 98), patients (aged 2-16 years) with recrudescent infections (1.54; n = 13), and pregnant women (1.61; n = 18). Individuals belonging to groups with a high risk of infection, as deduced by clinical epidemiology, did not harbour a higher number of clones per infection, nor greater parasite diversity than low-risk groups. In fact, multiple genotype infections were as common in low-risk groups, suggesting that there is frequent transmission of polyclonal infections from a single inoculum, rather than superinfection. Such a polyclonal transmission system would enable generation of extensive parasite diversity by recombination, despite the low level of transmission. However, co-infection with P. vivax was associated with fewer P. falciparum genotypes per infection
— id: 40125, year: 1999, vol: 93, page: 587, stat: Journal Article,

Malaria transmission and naturally acquired immunity to PfEMP-1
Piper KP; Hayward RE; Cox MJ; Day KP
1999 Dec;67(12):6369-6374, Infection & immunity
Why there are so few gametocytes (the transmission stage of malaria) in the blood of humans infected with Plasmodium spp. is intriguing. This may be due either to reproductive restraint by the parasite or to unidentified gametocyte-specific immune-mediated clearance mechanisms. We propose another mechanism, a cross-stage immunity to Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1). This molecule is expressed on the surface of the erythrocyte infected with either trophozoite or early gametocyte parasites. Immunoglobulin G antibodies to PfEMP-1, expressed on both life cycle stages, were measured in residents from an area where malaria is endemic, Papua New Guinea. Anti-PfEMP-1 prevalence increased with age, mirroring the decline in both the prevalence and the density of asexual and transmission stages in erythrocytes. These data led us to propose that immunity to PfEMP-1 may influence malaria transmission by regulation of the production of gametocytes. This regulation may be achieved in two ways: (i) by controlling asexual proliferation and density and (ii) by affecting gametocyte maturation
— id: 40129, year: 1999, vol: 67, page: 6369, stat: Journal Article,

Plasmodium falciparum: analysis of the antibody specificity to the surface of the trophozoite-infected erythrocyte
Piper KP; Roberts DJ; Day KP
1999 Feb;91(2):161-169, Experimental parasitology
Current opinion supports the view that immunity to the surface of the trophozoite-infected erythrocyte (IE) is to Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1). Here we provide further evidence using the mutant cell line 1776/C10 which no longer expresses PfEMP-1 at the IE surface, due to a subtelomeric deletion in chromosome 9. We have measured antibody reactivity to this mutant in comparison to it's intact isogenic parent line 1776, which does express PfEMP-1, using the sensitive technique of flow cytometry. IgG-specific antibodies (subclass IgG1) in the plasma of hyperimmune adults, reacted to 1776 but never to the 1776/C10 mutant. Antibody subclasses were also measured in individual plasma samples to the surface of trophozoite-IE. Predominantly IgG1 antibodies were detected, with a few individual plasma having additional IgG3 antibodies. Previous studies have used the agglutination assay to measure sero-conversion to PfEMP-1. Here we show that both agglutination and flow cytometric methods are comparable, suggesting that agglutination of trophozoite-IE is mediated by IgG antibodies. Comparison of the isogenic cell lines 1776 and 1776/C10 differing in expression of PfEMP-1 provides further evidence that IgG antibodies, in particular of the cytophilic subclasses, mediate recognition of PfEMP-1
— id: 40133, year: 1999, vol: 91, page: 161, stat: Journal Article,

Malaria -- a global threat
Day KP
Emerging infections : biomedical research reports San Diego : Academic Press, 1998,
— id: 4233, year: 1998, vol: , page: 463, stat: Chapter,

The biology of Plasmodium falciparum transmission stages
Day KP; Hayward RE; Dyer M
1998 ;116 Suppl(1):S95-109, Parasitology
The most important function of any parasite is to secure transmission to new hosts. The gametocyte, the stage which has become developmentally committed to the sexual cycle, provides a critical link in the transmission of Plasmodium falciparum from the human host to the anopheline mosquito vector. It is therefore imperative that our determination to understand the biology of the gametocyte is greater than the technical obstacles which have resulted in the gametocyte being left very much out of the limelight by the intensive investigation of the asexual bloodstream parasite. Here we explore the areas of gametocyte biology which by nature of their relevance to control and pathology as well as basic biology, are the subjects of investigation in our laboratory. We also point out areas in need of particular attention
— id: 40135, year: 1998, vol: 116 Suppl, page: S95, stat: Journal Article,

CD36-dependent adhesion and knob expression of the transmission stages of Plasmodium falciparum is stage specific
Day KP; Hayward RE; Smith D; Culvenor JG
1998 Jun 1;93(2):167-177, Molecular & biochemical parasitology
Plasmodium falciparum trophozoites sequester from the peripheral circulation by adherence to host endothelium. Gametocytes, also sequester during maturation. Analysis of the adhesion phenotype of stage I to V gametocytes of several isolates/clones was assessed by binding of infected cells to C32 melanoma cells (C32MC) and the purified adhesion proteins, leucocyte differentiation antigen (CD36) and intercellular adhesion molecule-1 (ICAM-1). These cells and proteins, have previously been shown to be receptors for adherence of trophozoites. Early gametocytes (stages I-IIA) were found to bind to C32MC as well as the purified receptor CD36 but not to ICAM-1. Early gametocytes bound to C32MC via CD36 and the parasite ligand involved in this binding was trypsin sensitive. Stage IIB to V gametocytes did not adhere to C32MC, CD36 nor ICAM-1. Electron-dense protruberances known as knobs and histidine rich protein 1 (HRP 1) expression have been associated with trophozite adhesion to CD36. Knobs were present at the surface of early but not late gametocyte infected cells. Stage-specific patterns of HRP 1 expression, consistent with a role for this molecule in CD36 adhesion of early gametocytes, were also observed. The adhesion phenotype of these young gametocytes was indistinguishable from that of the trophozoites by all criteria examined. These data support the hypothesis that other host receptors mediate the binding of late gametocytes
— id: 40136, year: 1998, vol: 93, page: 167, stat: Journal Article,

Transmission intensity and Plasmodium falciparum diversity on the northwestern border of Thailand
Paul RE; Hackford I; Brockman A; Muller-Graf C; Price R; Luxemburger C; White NJ; Nosten F; Day KP
1998 Feb;58(2):195-203, American journal of tropical medicine & hygiene
Genetic analysis of the number of Plasmodium falciparum genotypes per infected person in regions of holoendemic and hyperendemic malaria suggest that in areas of lower transmission intensity, significantly fewer parasite genotypes per infected person should be found. A predominance of single clone infections in the human population could generate the controversial clonal population structure proposed for P. falciparum by Tibayrenc and others. Characterization of P. falciparum from individuals on the Thai-Burmese border, an area of hypoendemic transmission, revealed a higher number of genotypes per infected person than that predicted. Possible reasons for this observation are discussed, with particular attention paid to human migration and multidrug resistance
— id: 40137, year: 1998, vol: 58, page: 195, stat: Journal Article,

Mating Patterns of Plasmodium falciparum
Paul, R E; Day, K P
1998 May;14(5):197-202, Parasitology today
Recent empirical data have enabled a more informed debate over the extent of clonality in Plasmodium falciparum populations. Oocyst heterozygosity data reveal that the mating structure of malaria populations varies according to the transmission intensity. This finding provides a more detailed picture of the malaria mating structure than previous conclusions, which were based on indirect measures of population mating structure, ie. linkage disequilibrium analyses. In this article, Ric Paul and Karen Day discuss aspects of the genetic structure of malaria populations as evidenced by oocyst heterozygosity and linkage disequilibrium data. They address the difficulties of performing genetic analyses of malaria parasite population structure inherent in parasite sampling, why two identical parasites are rarely observed in the field and how features of the epidemiology determine parasite population structure
— id: 70781, year: 1998, vol: 14, page: 197, stat: Journal Article,

Absence of malaria-specific mortality in children in an area of hyperendemic malaria
Maitland K; Williams TN; Peto TE; Day KP; Clegg JB; Weatherall DJ; Bowden DK
1997 Sep-Oct;91(5):562-566, Transactions of the Royal Society of Tropical Medicine & Hygiene
We conducted a prospective community-based malaria surveillance study on a cohort of children < 10 years old living in an area of hyperendemic malaria (spleen rates > 50% in children aged 2-9 years) in Vanuatu, Melanesia, supported by a concurrent prospective descriptive study of malaria admissions to the local hospital. The incidence of clinical malaria in children < 10 years old was 1.9 episodes/year. The annual incidence of severe malaria (severe malarial anaemia and cerebral malaria) was only 2/1000 in children aged < 5 years. The only manifestation of severe malaria seen in indigenous children was anaemia. No death could be attributed to malaria. While the incidence of uncomplicated clinical malaria in this population was comparable to that in many parts of Africa, the incidence of severe forms of the disease was significantly lower. This could not be attributed to differing rates of malaria transmission, chloroquine resistance, or to host protective or behavioural factors. These findings suggest that studies which compare disease patterns in geographically disparate populations may be instrumental in developing a better understanding of the determinants of clinical outcome in Plasmodium falciparum malaria and that such regional differences must be considered when planning or interpreting the effects of malaria interventions
— id: 40138, year: 1997, vol: 91, page: 562, stat: Journal Article,

Response: Self-Fertilization, Linkage Disequilibrium, and Strain in Plasmodium falciparum
Paul RE; Day KP
1996 Mar 1;271(5253):1300b-1301b, Science
— id: 78772, year: 1996, vol: 271, page: 1300b, stat: Journal Article,

Plasmodium falciparum: parasites defective in early stages of gametocytogenesis
Alano, P; Roca, L; Smith, D; Read, D; Carter, R; Day, K
1995 Sep;81(2):227-235, Experimental parasitology
Some molecular characteristics of Plasmodium falciparum lines which do not produce gametocytes are described. Parasites carrying a subtelomerically deleted chromosome 9 cannot form even the earliest forms of gametocytes, detectable with antibodies against the gametocyte-specific antigen Pfg27. In a parasite culture of clone HB3, in which both intact and deleted forms of chromosome 9 are present, full-length chromosome 9 molecules are retained mainly in gametocytes. These data suggest that the subtelomeric portion of chromosome 9 is required at an early stage of gametocytogenesis. Parasite subclones derived from gametocyte producing clone 3D7, which completely lost ability to produce gametocytes, are also described. Unlike the previous gametocyteless lines, these parasites stably maintain a full-length chromosome 9 and the ability to cytoadhere to C32 melanoma cells after prolonged asexual propagation. Their defect in sexual development is therefore genetically and functionally distinct from that of parasites carrying a deleted chromosome 9. Gametocyteless subclones derived from 3D7 do not produce any Pfg27 mRNA, while this gene is anomalously expressed in asexual stage parasites of two lines of a different genetic background, 1776sel8 and C10, one able and the other unable to produce gametocytes
— id: 70782, year: 1995, vol: 81, page: 227, stat: Journal Article,

Mating patterns in malaria parasite populations of Papua New Guinea
Paul RE; Packer MJ; Walmsley M; Lagog M; Ranford-Cartwright LC; Paru R; Day KP
1995 Sep 22;269(5231):1709-1711, Science
Description of the genetic structure of malaria parasite populations is central to an understanding of the spread of multiple-locus drug and vaccine resistance. The Plasmodium falciparum mating patterns from madang, Papua New Guinea, where intense transmission of malaria occurs, are described here. A high degree of inbreeding occurs in the absence of detectable linkage disequilibrium. This contrasts with other studies, indicating that the genetic structure of malaria parasite populations is neither clonal nor panmictic but will vary according to the transmission characteristics of the region
— id: 40139, year: 1995, vol: 269, page: 1709, stat: Journal Article,

Mapping the genetic locus implicated in cytoadherence of Plasmodium falciparum to melanoma cells
Barnes, D A; Thompson, J; Triglia, T; Day, K; Kemp, D J
1994 Jul;66(1):21-29, Molecular & biochemical parasitology
Many lines of Plasmodium falciparum undergo a deletion of the right end of chromosome 9 during in vitro cultivation accompanied by loss of cytoadherence to melanoma cells. The deletion also results in loss of expression of PfEMP1, the putative cytoadherence ligand, suggesting that PfEMP1 or a regulatory gene controlling PfEMP1 expression is encoded in this region. Initially a library of short fragments highly enriched for the right arm of chromosome 9 was constructed in bacteriophage lambda. Clones from this library were obtained randomly by the polymerase chain reaction (PCR) technique, sequenced and used to screen a yeast artificial chromosome (YAC)-P. falciparum library by PCR so that the region could be cloned and physically mapped in detail. We have used probes from this region to demonstrate that clones derived from ITG2 have undergone a deletion of intermediate length on chromosome 9. This could explain the unusual stability of cytoadherence in these clones
— id: 70783, year: 1994, vol: 66, page: 21, stat: Journal Article,

Dynamics of malaria parasitaemia associated with febrile illness in children from a rural area of Madang, Papua New Guinea
Cox MJ; Kum DE; Tavul L; Narara A; Raiko A; Baisor M; Alpers MP; Medley GF; Day KP
1994 Mar-Apr;88(2):191-197, Transactions of the Royal Society of Tropical Medicine & Hygiene
Active community and self-reporting surveillance techniques have been used to describe the dynamics of febrile illness and associated malaria infection in children aged 2 to 15 years from a rural area of Madang Province, Papua New Guinea (PNG). Both history of fever and fever in association with parasitaemia appeared to be reliable indicators of malaria morbidity in this endemic area. Parasite density was observed to be a major determinant of mild malarial disease at both the population level and within an individual. Age-specific prevalence of febrile illness correlated with age-specific patterns of parasite density but not of parasite prevalence. Seasonal changes in fever incidence correlated with parasite density. The transition from afebrile to febrile state within an individual was generally associated with an increase in parasite density. Surveillance and self-reported febrile cases (which differ in severity on the basis of the perceived need for treatment) could be distinguished on the basis of parasite density. Thus surveillance techniques divide clinical malaria in rural PNG into 'mild' and 'very mild' forms. The age-specific pattern of decline of prevalence of malaria-associated febrile illness and parasite density is best explained by induction of strain-specific anti-disease immunity upon infection with a given strain of Plasmodium falciparum. The fever threshold in self-reporting febrile cases was seen to decrease with age and can be explained by an age-specific decline in anti-toxic immunity
— id: 40143, year: 1994, vol: 88, page: 191, stat: Journal Article,

A theoretical framework for the immunoepidemiology of Plasmodium falciparum malaria
Gupta S; Day KP
1994 Jul;16(7):361-370, Parasite immunology
Molecular genetic analyses of P. falciparum have led to the cloning and sequencing of a number of antigens that are potential candidates for vaccination against malaria. Seroepidemiological studies in endemic areas have attempted to assess the relative importance of these antigens in protection against malaria. In this paper, we attempt to evaluate the relative contributions of conserved and strain-specific immune responses by modelling their influence of age-specific patterns of infection and disease. The modelling exercises in this paper clearly demonstrate that the observed patterns of age-prevalence are best explained by proposing that the accumulation to a threshold of an immune response against a conserved determinant is required for protection against infection, while 'anti-disease' immunity develops more linearly with exposure. This is compatible with the conjecture that the parasite population is structured into several independently transmitted strains, that each confers some degree of 'anti-disease' immunity, but does not protect against further infection by the same strain. Within this framework, the average duration of parasitaemia increases with age, as previously encountered strains endure for longer periods at a subclinical level. Indirect evidence for the increase in duration of parasitaemia with age may be obtained from a comparison of age-prevalence curves between dry and rainy seasons. By using mathematical methods to structure epidemiological and immunological information, we provide a coherent theoretical framework for the dissection of the important components of naturally acquired immunity to malaria
— id: 40141, year: 1994, vol: 16, page: 361, stat: Journal Article,

Parasite virulence and disease patterns in Plasmodium falciparum malaria
Gupta S; Hill AV; Kwiatkowski D; Greenwood AM; Greenwood BM; Day KP
1994 Apr 26;91(9):3715-3719, Proceedings of the National Academy of Sciences of the United States of America
Heterogeneity in parasite virulence is one of several factors that have been proposed to contribute to the wide spectrum of disease severity in Plasmodium falciparum malaria. We used observed age-structured patterns of disease to define a population structure of P. falciparum, where the latter contains several independently transmitted antigenic types or 'strains' that each induce some degree of strain-specific antidisease immunity upon infection. Patterns of incidence of severe and mild disease may be explained by assuming that a majority of these strains are associated with mild disease and that although severe malarial anemia is a complication occurring in a certain proportion of early infections with 'mild' parasites, cerebral malaria is caused by a few distinct highly virulent strains. Considerable variation in parasite virulence, as a major factor of disease severity in malaria, is made possible by the absence of competition between the various parasite strains, arising from weak shared immune responses. The theoretical framework presented in this paper can explain other epidemiological observations, such as the results of interventions with insecticide-impregnated bednets
— id: 40142, year: 1994, vol: 91, page: 3715, stat: Journal Article,

Antigenic diversity and the transmission dynamics of Plasmodium falciparum
Gupta S; Trenholme K; Anderson RM; Day KP
1994 Feb 18;263(5149):961-963, Science
The average age of humans at their first infection with Plasmodium falciparum is typically less than 1 year in most endemic areas. This has been interpreted as evidence of the high transmissibility of the parasite, with the implication that control of malaria will require high levels of coverage with a potential vaccine. This interpretation is challenged by mathematical models that demonstrate that the long period required to develop immunity to malaria permits a high risk (or low average age) of infection even when parasite transmissibility is low. Patterns of seroconversion to five antigenically distinct isolates of P. falciparum in a highly malarious area of Papua New Guinea indicate that each is only mildly transmissible and that malaria, as a construct of several such independently transmitted strains, has a basic reproductive rate (or transmissibility) that is an order of magnitude lower than other estimates
— id: 40144, year: 1994, vol: 263, page: 961, stat: Journal Article,

Antifilarial IgG4 antibodies in children from filaria-endemic areas correlate with duration of infection and are dissociated from antifilarial IgE antibodies
Mahanty S; Day KP; Alpers MP; Kazura JW
1994 Nov;170(5):1339-1343, Journal of infectious diseases
To investigate the relationship of antifilarial IgG4 and IgE to the intensity of transmission and duration of filarial infections in endemic populations, antifilarial antibody levels in children residing in a village in Papua New Guinea where transmission of Wuchereria bancrofti was reduced by repeated insecticide spraying were compared with levels in residents of three nearby villages where no control measures had been used. Antifilarial IgG4 levels were significantly lower in children from the sprayed village than in children or adults in nonsprayed villages (P < .01) and correlated with age (P < .05) and intensity of microfilaremia (P < .01). In contrast, antifilarial IgE was elevated to similar levels in children and adults from both villages. Antifilarial IgG4 (and not IgE) levels in endemic populations appear to be directly related to the duration of infection or to the cumulative exposure to infective vectors
— id: 40140, year: 1994, vol: 170, page: 1339, stat: Journal Article,

The S-antigen of Plasmodium falciparum: repertoire and origin of diversity
Bickle, Q; Anders, R F; Day, K; Coppel, R L
1993 Oct;61(2):189-196, Molecular & biochemical parasitology
S-antigens are heat-stable, highly polymorphic proteins released by Plasmodium falciparum at the time of schizont rupture. Previously determined S-antigen sequences allowed the proposal of a general gene structure consisting of 5 sequence blocks. The sequence of the central block of tandem repeats provides a useful means of distinguishing the S-antigen allele and also its serotype, whereas the amino and carboxy terminal sequences defined the S-antigen family, 4 of which have been described. We present the sequence of 3 new S-antigen alleles, for the isolates HB3, KF1916 and KF1917. The allele-defining repeat sequence is ETGPGKAGEQG for HB3, GDQTEGS(S/A)GGK for KF1917 and AGSNE(E/K) for KF1916. The sequences of these newly described S-antigens are consistent with the proposed general gene structure and all belong to defined families, although carboxy-terminal sequences appear to be much more variable within a family than previously realised
— id: 70784, year: 1993, vol: 61, page: 189, stat: Journal Article,

Genes necessary for expression of a virulence determinant and for transmission of Plasmodium falciparum are located on a 0.3-megabase region of chromosome 9
Day KP; Karamalis F; Thompson J; Barnes DA; Peterson C; Brown H; Brown GV; Kemp DJ
1993 Sep 1;90(17):8292-8296, Proceedings of the National Academy of Sciences of the United States of America
Virulence of the human malaria parasite Plasmodium falciparum is believed to relate to adhesion of parasitized erythrocytes to postcapillary venular endothelium (asexual cytoadherence). Transmission of malaria to the mosquito vector involves a switch from asexual to sexual development (gametocytogenesis). Continuous in vitro culture of P. falciparum frequently results in irreversible loss of asexual cytoadherence and gametocytogenesis. Field isolates and cloned lines differing in expression of these phenotypes were karyotyped by pulse-field gel electrophoresis. This analysis showed that expression of both phenotypes mapped to a 0.3-Mb subtelomeric deletion of chromosome 9. This deletion frequently occurs during adaptation of parasite isolates to in vitro culture. Parasites with this deletion did not express the variant surface agglutination phenotype and the putative asexual cytoadherence ligand designated P. falciparum erythrocyte membrane protein 1, which has recently been shown to undergo antigenic variation. The syntenic relationship between asexual cytoadherence and gametocytogenesis suggests that expression of these phenotypes is genetically linked. One explanation for this linkage is that both developmental pathways share a common cytoadherence mechanism. This proposed biological and genetic linkage between a virulence factor (asexual cytoadherence) and transmissibility (gametocytogenesis) would help explain why a high degree of virulence has evolved and been maintained in falciparum malaria
— id: 40145, year: 1993, vol: 90, page: 8292, stat: Journal Article,

Population genetics and dynamics of Plasmodium falciparum: an ecological view
Day KP; Koella JC; Nee S; Gupta S; Read AF
1992 ;104 Suppl(17):S35-S52, Parasitology
Molecular characterization of the Plasmodium falciparum genome has led to identification of polymorphic loci and the mechanisms generating genetic diversity in this parasite. This information has resulted in the development of molecular methods to type parasite diversity in the field. Consequently, we are now in a position to describe the population genetics and dynamics of P. falciparum. The limited number of field studies that have been conducted to date have revealed an extraordinary degree of genetic diversity in natural parasite populations. Heterozygous recombination which occurs during meiosis appears to be one mechanism for generating genetic diversity. The rate at which such recombination occurs in natural parasite populations defines the genetic structure of the parasite population and can influence the ability of the parasite to respond to selection pressure. The high frequency of single genotype infections and the female-biased gametocyte sex ratios found in hyperendemic malaria areas suggest that self-fertilization occurs frequently. Population-wide surveys of allele frequencies in endemic areas have, however, shown no evidence of linkage disequilibrium and are consistent with a panmictic population structure. We argue that these studies have only sampled symptomatic infections, within which rare or recombinant genotypes may be disproportionately represented. They also take no account of the spatial structure of P. falciparum populations. Systematic investigations of the amount of heterozygosity in small areas as part of population-wide surveys are required to define the genetic structure of P. falciparum populations. Population dynamic studies which consider genetic heterogeneity of P. falciparum have shown fluctuations of different serotypes in space and time. The host immune response appears to play an important role in generating these dynamics. Integrated field and laboratory studies, which consider the interaction between population genetics and dynamics, will be necessary to describe the population biology of P. falciparum
— id: 40147, year: 1992, vol: 104 Suppl, page: S35, stat: Journal Article,

A chromosome 9 deletion in Plasmodium falciparum results in loss of cytoadherence
Kemp DJ; Thompson J; Barnes DA; Triglia T; Karamalis F; Petersen C; Brown GV; Day KP
1992 ;87 Suppl 3(17):85-89, Memorias do Instituto Oswaldo Cruz
Many lines of Plasmodium falciparum undergo a deletion of the right end of chromosome 9 during in vitro culture accompanied by loss of cytoadherence and gametocytogenesis. Selection of cytoadherent cells from a mixed population co-selects for those with an undeleted chromosome 9 and the selected cells produce gametocytes. The deletion also results in loss of expression of PfEMP1, the putative cytoadherence ligand, suggesting that PfEMP1 or a regulatory gene controlling PfEMP1 expression and gametocytogenesis may be encoded in this region. We have isolated several markers for the deleted region and are currently using a YAC-P. falciparum library to investigate this region of the genome in detail
— id: 40148, year: 1992, vol: 87 Suppl 3, page: 85, stat: Journal Article,

Gametocyte sex ratios as indirect measures of outcrossing rates in malaria
Read AF; Narara A; Nee S; Keymer AE; Day KP
1992 Jun;104 ( Pt 3)(17):387-395, Parasitology
The frequency of recombination between unlike genotypes is central to understanding the generation of genetic diversity in natural populations of malaria. Here we suggest a way of investigating the problem which could complement conventional biochemical approaches to the population genetics of malaria. Sex allocation theory is one of the most successful areas of evolutionary biology. A well-supported prediction is that progressively less female-biased sex ratios are favoured with more outcrossing; equal numbers of males and females being evolutionarily stable in randomly mating outbred populations. We present a simple game theory model to support the idea that outcrossing rates in malaria will be correlated with the sex ratio of gametocytes in the peripheral blood of vertebrate hosts. Blood films from epidemiological surveys and culture-adapted isolates from Madang Province, Papua New Guinea, were used to estimate average gametocyte sex ratio of Plasmodium falciparum in the area. The geometric mean proportion of males in the population was 0.18 (95% confidence limits: 0.15-0.22). From our model, we estimate that, on average, 36% of zygotes are the result of outcrossing. This estimate assumes that most microgametes released following exflagellation are capable of fertilization. If, on average, fewer than about 70% of microgametes are capable of fertilization (as is the case in at least one other species of Plasmodium), the observed sex ratio would be consistent with between zero and 36% of zygotes being the result of outcrossing. These estimates suggest that there is usually a numerically dominant genotype in the gametocyte population in a blood meal, and that a considerable amount of selfing is occurring in P. falciparum populations in the Madang region, even though it is an area of intense year-round transmission
— id: 40146, year: 1992, vol: 104 ( Pt 3), page: 387, stat: Journal Article,

Plasmodium falciparum ring-infected erythrocyte surface antigen is released from merozoite dense granules after erythrocyte invasion
Culvenor JG; Day KP; Anders RF
1991 Mar;59(3):1183-1187, Infection & immunity
Electron microscopy was used to study the fate of Plasmodium falciparum ring-infected erythrocyte surface antigen after merozoite invasion by using postembedding immunolabeling. The antigen was localized to small dense granules located centrally or laterally in free merozoites. In newly invaded erythrocytes, labeling was found in pockets of the parasitophorous vacuole space or in aggregates closely associated with the parasitophorous vacuole. These patterns indicate that ring-infected erythrocyte surface antigen is contained in merozoite dense granules that are released after merozoite invasion and not via apical rhoptry ducts at the time of merozoite attachment
— id: 40154, year: 1991, vol: 59, page: 1183, stat: Journal Article,

Age-specific acquisition of immunity to infective larvae in a bancroftian filariasis endemic area of Papua New Guinea
Day KP; Gregory WF; Maizels RM
1991 May;13(3):277-290, Parasite immunology
The development of antibodies to infective stages of the filarial parasite, Wuchereria bancrofti, with age of the host human population was studied by immunofluorescence, immunoprecipitation and immunoblotting assays. Among individuals under 20 years of age, few had detectable antibodies to the infective (L3) larval surface by IFA: only 2 out of 10 scored positive. However, all adults (over 20 years) were positive in this assay although the utilization of isotypes varied between different individuals. Whilst antibodies to the L3 surface are therefore acquired after prolonged exposure to infection (greater than 20 years), recognition patterns of L3 surface labelled antigens, measured by immunoprecipitation analysis iodinated proteins on SDS-PAGE, and of somatic L3 proteins on immunoblots, were equivalent in the two age groups. Thus, a critical surface antigen, recognised in an age-dependent manner, is present on the L6 cuticle but cannot be resolved as a conventional protein or glycoprotein constituent
— id: 40151, year: 1991, vol: 13, page: 277, stat: Journal Article,

Age specific patterns of change in the dynamics of Wuchereria bancrofti infection in Papua New Guinea
Day KP; Grenfell B; Spark R; Kazura JW; Alpers MP
1991 May;44(5):518-527, American journal of tropical medicine & hygiene
Results of a longitudinal study of the age-specific dynamics of Wuchereria bancrofti infection in a community of East Sepik Province, Papua New Guinea (PNG) are described. Microfilarial (mf) density and serum levels of W. bancrofti phosphorylcholine-containing antigen (PC-Ag) in individuals were used as indirect measures of adult worm burden. These parasitological data were collected from 126 subjects greater than 4 years of age at two time points, 12 months apart, prior to the administration of the antifilarial drug diethylcambamazine (DEC). No significant changes in levels of mf density were observed for the study population between these two time points. However, significant changes in the levels of circulating PC-Ag were noted in subjects less than or equal to 20 years of age, but not in subjects greater than 20 years of age, between these two time points. The apparent shorter half life of circulating PC-Ag compared to that of mf makes antigenemia a more sensitive measure of the dynamics of adult worm populations. These data are discussed in terms of a basic mathematical model describing the dynamics of adult worm populations in relation to their life expectancy and attrition of larvae during establishment. Consideration of these data in the context of this simple immigration/death model suggests that the differences observed in patterns of change in intensity of infection between subjects less than or equal to 20 years old and those greater than 20 years old may be consistent with the acquisition of resistance to superinfection with increasing age
— id: 40150, year: 1991, vol: 44, page: 518, stat: Journal Article,

Naturally acquired immunity to Plasmodium falciparum
Day KP; Marsh K
1991 Mar;12(3):A68-A71, Immunology today
Malaria infections induce multiple humoral and cellular responses, most of which are probably not protective. This discussion of the epidemiology of acquired immunity to malaria will concentrate on two main areas: first, the relationship between parasitism and disease in endemic settings and the constraints placed on determining which responses are important in acquired protective immunity; second, the central importance of antigenic diversity in the host-parasite relationship. The emphasis throughout, unless otherwise stated, will be on the major human pathogen Plasmodium falciparum
— id: 40152, year: 1991, vol: 12, page: A68, stat: Journal Article,

Serological evaluation of the macrofilaricidal effects of diethylcarbamazine treatment in bancroftian filariasis
Day KP; Spark R; Garner P; Raiko A; Wenger JD; Weiss N; Mitchell GF; Alpers MP; Kazura JW
1991 May;44(5):528-535, American journal of tropical medicine & hygiene
An Mr 200,000 phosphorylcholine-containing antigen (PC-Ag) of predominantly adult worm origin was found in the sera of humans infected with Wuchereria bancrofti. This paper describes results of a longitudinal study of changes in levels of PC-Ag in response to diethylcarbamazine (DEC) therapy as measured by two-site immunoradiometric assay (IRMA) and Western blotting. One hundred thirty-two residents of a bancroftian filariasis-endemic area of Papua New Guinea (PNG) were treated with a 72 mg/kg dose of DEC. A macrofilaricidal effect was seen with this dose of DEC as 34% of the treated subjects had localized side effects and long-term decreases in microfilariae (mf) counts were observed 12 months after treatment. The PC-Ag levels were reduced to 72%, 52%, and 51% of pretreatment values at 21 days and at six and 12 months after treatment. These decreases, observed by IRMA, were specifically associated with loss of the Mr 200,000 PC-Ag detected by immunoadsorption and Western blotting. From drug treatment data, the maximum half-life of PC-Ag in circulation was calculated to be 50 days, assuming a first-order decay process. This maximum half-life indicates that persistent antigenemia observed in the majority of treated subjects could only result from the survival of adult worms. In the absence of methods to directly demonstrate W. bancrofti adult worms, detection of serum PC-Ag levels provides a sensitive indirect measure of the dynamics of adult worm populations. This serological measurement may be useful in optimizing the macrofilaricidal and therapeutic effects of DEC and in assessing the macrofilaricidal action of new antifilarial drugs and immunological interventions
— id: 40149, year: 1991, vol: 44, page: 528, stat: Journal Article,

Structural diversity in the Plasmodium falciparum merozoite surface antigen 2
Smythe JA; Coppel RL; Day KP; Martin RK; Oduola AM; Kemp DJ; Anders RF
1991 Mar 1;88(5):1751-1755, Proceedings of the National Academy of Sciences of the United States of America
Antigens associated with the surface of merozoites of the malaria parasite Plasmodium falciparum are directly accessible to immune attack and therefore are prime vaccine candidates. We have previously shown that one of the two known merozoite surface antigens (merozoite surface antigen 2; MSA-2) exhibits considerable sequence and antigenic diversity in different isolates. The sequences of MSA-2 from three isolates revealed a central domain composed of repeats that vary in number, length, and sequence, flanked in turn by nonrepetitive variable sequences and by conserved N- and C-terminal domains. We report here the sequences of a further four MSA-2 alleles, containing repetitive sequences that are related but not identical to each other. The seven alleles of MSA-2 can be divided into two distinct allele families on the basis of nonrepetitive sequences. Hybridization studies with repeat probes indicated that all of the 44 P. falciparum isolates examined contained repeat regions similar to those defined in known MSA-2 sequences
— id: 40153, year: 1991, vol: 88, page: 1751, stat: Journal Article,

Knob-independent cytoadherence of Plasmodium falciparum to the leukocyte differentiation antigen CD36
Biggs BA; Gooze L; Wycherley K; Wilkinson D; Boyd AW; Forsyth KP; Edelman L; Brown GV; Leech JH
1990 Jun 1;171(6):1883-1892, Journal of experimental medicine
The survival of Plasmodium falciparum-infected erythrocytes is enhanced by the sequestration of mature trophozoites and schizonts from the peripheral circulation. Cytoadherence of infected erythrocytes in vivo is associated with the presence of knobs on the erythrocyte surface, but we and others have shown recently that cytoadherence to C32 melanoma cells may occur in vitro in the absence of knobs. We show here that a knobless clone of P. falciparum adheres to the leukocyte differentiation antigen, CD36, suggesting that binding to CD36 is independent of the presence of knobs on the surface of the infected erythrocyte. This clone showed little cytoadherence to immobilized thrombospondin or to endothelial cells expressing the intercellular adhesion molecule 1. Furthermore, an Mr approximately 300-kD trypsin-sensitive protein doublet was immunoprecipitated from knobless trophozoite-infected erythrocytes. Finding a P. falciparum erythrocyte membrane protein 1 (PfEMP1)-like molecule on these infected erythrocytes is consistent with a role for PfEMP1 in cytoadherence to CD36 and C32 melanoma cells
— id: 45575, year: 1990, vol: 171, page: 1883, stat: Journal Article,

The relationship between splenomegaly and antibody to the circumsporozoite protein of Plasmodium falciparum in two groups of women with high and low enlarged spleen rates in Madang, Papua New Guinea
Brabin L; Burkot TR; Brabin BJ; Crane GG; Forsyth KP; Alpers MP; Van der Kaay HJ
1990 Jan-Feb;84(1):40-45, Transactions of the Royal Society of Tropical Medicine & Hygiene
The objective of this study was to determine the prevalence of antibodies recognizing the circumsporozoite (CS) protein of Plasmodium by an enzyme-linked immunosorbent assay, in 2 subpopulations of women with significantly different enlarged spleen rates but similar exposure to malaria, on the north coast of Papua New Guinea. Antibody levels of immunoglobulin G (IgG) antibody to CS protein in the high and low spleen rate groups were similar (56.2% and 55.1%) but there was a significant difference in IgM (29.6% and 16.7%). In neither group did antibodies increase with parity (age). In both groups a high level of either IgG or IgM antibody to CS protein was associated with a high spleen rate and women with hyper-reactive malarious splenomegaly were more likely to be positive for both. Lower parasite rates were associated only with increased IgM antibody titres. High levels of antibody to blood-stage parasites were also present in the high spleen rate group, suggesting that antibodies to the CS protein were not protective. It is considered that cell-mediated immunity may be deficient in women with persistent splenomegaly
— id: 45577, year: 1990, vol: 84, page: 40, stat: Journal Article,

Several alleles of the multidrug-resistance gene are closely linked to chloroquine resistance in Plasmodium falciparum
Foote, S J; Kyle, D E; Martin, R K; Oduola, A M; Forsyth, K; Kemp, D J; Cowman, A F
1990 May 17;345(6272):255-258, Nature
The lethal form of human malaria caused by Plasmodium falciparum is virtually uncontrollable in many areas because of the development of drug resistance, in particular chloroquine resistance (CQR). CQR is biologically similar to the multiple drug resistance phenotype (MDR) of mammalian tumour cells, as both involve expulsion of drug from the cell and both can be reversed by calcium channel antagonists. A homologue (pfmdr1) of the mammalian multidrug resistance gene has been implicated in CQR because it is amplified in some CQR isolates of P. falciparum as is an mdr gene in MDR tumour cells. We show here that the complete sequences of pfmdr1 genes from 2 CQ sensitive (CQS) P. falciparum isolates are identical. In 5 CQR isolates, 1-4 key nucleotide differences resulted in amino acid substitutions. On the basis of these substitutions, we have correctly predicted the CQS/CQR status of a further 34 out of 36 isolates. This is a paradox as CQR arises much less frequently than would be predicted if single point mutations were sufficient. We conclude that a mutated pfmdr1 gene is one of at least two mutated genes required for CQR
— id: 70785, year: 1990, vol: 345, page: 255, stat: Journal Article,

Filarial-specific IgG4 response correlates with active Wuchereria bancrofti infection
Kwan-Lim GE; Forsyth KP; Maizels RM
1990 Dec 15;145(12):4298-4305, Journal of immunology
The filarial-specific humoral immune response of adult residents of two areas of Papua New Guinea, differing in transmission of Wuchereria bancrofti infection was compared. The majority of residents of the village of Bonahoi, in an area where transmission of filariasis had been interrupted by a 20-year insecticide spray program to control malaria, showed no parasitologic signs of active W. bancrofti infection and were negative for both circulating phosphorylcholine Ag and peripheral blood microfilariae. In contrast, adult residents of the village of Nanaha were in an area exposed to infection, and were phosphorylcholine-Ag- and microfilariae-positive. The antibody response of these two groups to both adult worm excretory/secretory (ES) Ag and somatic antigen extract was examined to determine which components of the filarial-specific immune response were dependent on active infection. Identification of these immune responses may point to immunologic methods to evaluate control programs for lymphatic filariasis. Adults from Bonahoi were found to have significant immune responses to [35S] methionine-labeled ES Ag by immunoprecipitation and to adult somatic antigen extracts by ELISA and by immunoblotting. This result is consistent with the fact that these individuals were previously exposed to and/or infected with W. bancrofti. Similarly, residents of the endemic village had detectable immune responses to these Ag irrespective of if they were microfilaremic. The most striking immunologic difference observed between the two groups was that residents of Bonahoi had a dramatically reduced filarial-specific IgG4 antibody response to both adult somatic Ag and adult ES Ag. These data suggest that longitudinal measurement of filarial-specific IgG4 levels may be a useful seroepidemiologic indicator of changes in W. bancrofti infection status
— id: 45574, year: 1990, vol: 145, page: 4298, stat: Journal Article,

Chromosome 9 from independent clones and isolates of Plasmodium falciparum undergoes subtelomeric deletions with similar breakpoints in vitro
Shirley MW; Biggs BA; Forsyth KP; Brown HJ; Thompson JK; Brown GV; Kemp DJ
1990 Apr;40(1):137-145, Molecular & biochemical parasitology
We show that chromosome 9 in all isolates and clones of Plasmodium falciparum examined so far exists as one of two distinctly different forms, a large form about 1.9 megabases long or a smaller form about 25% shorter. Physical maps of chromosome 9 from independent clones with large and small forms of chromosome 9, and from an isolate with the large form and 3 derived clones with the small form reveal the underlying structural basis of this size polymorphism. The small form differs from the large only in that there are subtelomeric deletions at each end, one of these deletions involving about 0.45 megabases. Remarkably, the breakpoints map within about +/- 1% of the total chromosome length for each of these populations. We discuss some possible mechanisms for this
— id: 45576, year: 1990, vol: 40, page: 137, stat: Journal Article,

Antigenic diversity of the asexual blood stages of Plasmodium falciparum
Anders RF; Smythe JA; Barzaga NG; Forsyth KP; Brown HJ; Crwther PE; Thomas LM; Coppel RL; Culvenor JG; Brown GV
New strategies in parasitology [S.l.] : Churchill Livingstone, 1989,
— id: 4235, year: 1989, vol: , page: ?, stat: Chapter,

Two populations of women with high and low spleen rates living in the same area of Madang, Papua New Guinea, demonstrate different immune responses to malaria
Brabin BJ; Brabin L; Crane G; Forsyth KP; Alpers MP; van der Kaay HJ
1989 Sep-Oct;83(5):577-583, Transactions of the Royal Society of Tropical Medicine & Hygiene
Specific malaria and total IgM antibody responses were measured in 2 linguistically distinct coastal Papua New Guinean populations living in the same endemic malarious area, but exhibiting different adult female spleen rates (51% and 30%), in order to establish whether the higher spleen rates in the former group were due to hyper-reactive malarious splenomegaly (HMS). Malaria parasite rates were comparable, and geometric mean titres of IgG malaria antibody were the same, in both groups, indicating comparable exposure to malaria. A higher mean total IgM was observed in the high spleen (HS) rate group (6.07 g/litre, compared with 4.62 g/litre), a higher proportion was seropositive for IgM antibody to Plasmodium falciparum (63% compared with 54%), and HMS was found rather more frequently (4.7% compared with 2.6%). In both groups total IgM concentrations increased significantly with rising parity, and the mean level of 5.27 g/litre in young nulliparous women from the HS group suggested that IgM levels in this group at least were elevated from childhood. In both groups a rise in total IgM was associated with higher P. falciparum IgM geometric mean titres of antibody activity, a fall in parasite rates (HS group: 30% to 15%, P = 0.02; LS group: 24% to 0%, P = 0.034), and higher spleen rates (HS group: 38% to 65%, P = 0.001; LS group: 20% to 67%, P = 0.00012). It is concluded that the difference in spleen rates between the 2 groups was the result of differing degrees of acquired immunity to malaria, probably due to genetic differences in immune responses.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 45578, year: 1989, vol: 83, page: 577, stat: Journal Article,

Specific detection of human antibodies to Onchocerca volvulus
Cabrera, Z; Parkhouse, R M; Forsyth, K; Gomez Priego, A; Pabon, R; Yarzabal, L
1989 Dec;40(4):454-459, Tropical medicine & parasitology
Specific diagnosis of antibodies to Onchocerca was achieved through (1) the construction of direct and indirect ELISA systems, and (2) restricting ELISA assays to the IgG4 class. The direct ELISA was based on the isolation of a surface derived, low molecular weight surface antigen preparation containing two main antigens (M. wt. 16.2 and 12.8 kDA) as defined by Western blot analysis. The direct ELISA system detected antibodies in children of six years old, and may therefore be applicable to detecting reinvasion in OCP areas of Onchocerca volvulus control. The indirect ELISA system was a competitive binding ELISA-based assay using a monoclonal antibody recognising two Onchocerca components (M. wts. 15.6 and 25.9) on a Western blot. The direct and indirect ELISA systems were similarly specific and sensitive when evaluated in a preliminary survey. The direct ELISA system yielded a specificity and sensitivity of: 100% and 100% respectively, using Mexican endemic and Mexican intestinal nematode infection sera as positive and negative controls respectively: 91% and 96% respectively, using Venezuelan endemic and Venezuelan Mansonella ozzardi infection sera as positive and negative controls, respectively: 87% and 93% respectively, using African endemic and Papuan (New Guinea) Wuchereria bancrofti infection sera as positive and negative controls respectively: 93% and 93% respectively, using African endemic and Indian W. bancrofti infection sera as positive and negative controls respectively. Similar specificity and sensitivity levels were obtained when the same comparisons were made using the indirect (inhibition) ELISA assay. These values may be contrasted with the currently used PBS extract of O. volvulus which yielded specificities of less than 10% in all the above comparisons.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 70786, year: 1989, vol: 40, page: 454, stat: Journal Article,

Small area variation in prevalence of an S-antigen serotype of Plasmodium falciparum in villages of Madang, Papua New Guinea
Forsyth KP; Anders RF; Cattani JA; Alpers MP
1989 Apr;40(4):344-350, American journal of tropical medicine & hygiene
Cross-sectional and longitudinal village-based studies of the transmission dynamics of an S-antigen serotype of the asexual erythrocyte stages of Plasmodium falciparum have been carried out in Madang, Papua New Guinea (PNG). Sera collected from village residents were screened for circulating S-antigen of the FC27 serotype by enzyme-linked immunosorbent assay (ELISA). The prevalence of the FC27 S-antigen was found to vary between villages at a given point in time, as well as within a village over time. Residents of villages 2-5 km apart were infected with P. falciparum of different S-antigen serotypes. This study documents the periodic nature of transmission of a sub-population of P. falciparum defined by the FC27 S-antigen. The variation in a small area in the prevalence of this serotype of P. falciparum in Madang illustrates the complexities of malaria transmission which must be considered in the design of malaria vaccine trials
— id: 45581, year: 1989, vol: 40, page: 344, stat: Journal Article,

Diversity of antigens expressed on the surface of erythrocytes infected with mature Plasmodium falciparum parasites in Papua New Guinea
Forsyth KP; Philip G; Smith T; Kum E; Southwell B; Brown GV
1989 Sep;41(3):259-265, American journal of tropical medicine & hygiene
Antigens were detected on the surface of erythrocytes from children with acute falciparum malaria in Madang, Papua New Guinea. These parasite-induced erythrocyte surface antigens (PIESA) were serotyped with convalescent sera from children and hyperimmune sera from adults in parasite infected cell agglutination assays (PICAs) and by inhibition of binding of infected cells to melanoma cells. Extensive serological diversity of PIESA was demonstrated. A significant correlation between serotypes defined by reactivity of immune sera in PICA and inhibition of melanoma cell binding (MCB) was observed. This suggests that both assays measure antibody responses to the same antigen(s). Increased recognition of different PIESA specificities with age is consistent with the hypothesis that repeated exposure to malaria confers immunity against a range of PIESA serotypes and parallels the development of clinical immunity to malaria in this area of Papua New Guinea
— id: 45579, year: 1989, vol: 41, page: 259, stat: Journal Article,

The effect of iron therapy on malarial infection in Papua New Guinean schoolchildren
Harvey, P W; Heywood, P F; Nesheim, M C; Galme, K; Zegans, M; Habicht, J P; Stephenson, L S; Radimer, K L; Brabin, B; Forsyth, K
1989 Jan;40(1):12-18, American journal of tropical medicine & hygiene
The effect of iron therapy on malarial infection was investigated in Papua New Guinea, where malaria is endemic. Prepubescent schoolchildren with hemoglobin levels of 8-12 g/dl were randomly assigned to receive either 200 mg ferrous sulfate or a placebo twice daily for 16 weeks. Iron status and malarial infection were assessed at baseline, after 6 and 16 weeks of therapy, and 8 weeks after therapy was discontinued. Iron status was significantly improved by the treatment. The treatment did not significantly affect parasite rate, parasite density, or levels of anti-malarial IgG. No changes in spleen size were observed in either group. Furthermore, there was no significant difference between the groups in reported episodes of suspected malaria during the therapy. These results suggest that, in malaria endemic areas, oral treatment for iron deficiency can be carried out in semi-immune or immune schoolchildren without adverse consequences
— id: 70787, year: 1989, vol: 40, page: 12, stat: Journal Article,

Field applications of agglutination and cytoadherence assays with Plasmodium falciparum from Papua New Guinea
Southwell BR; Brown GV; Forsyth KP; Smith T; Philip G; Anders R
1989 Jul-Aug;83(4):464-469, Transactions of the Royal Society of Tropical Medicine & Hygiene
Plasmodium falciparum isolates obtained directly from patients in Papua New Guinea were tested in their first cycle of growth in vitro for adherence to melanoma cells and for susceptibility to agglutination by immune serum. Binding varied among isolates and, in many cases, increased with further rounds of replication under optimal culture conditions. Binding inhibition assays and agglutination assays demonstrated extreme heterogeneity of surface antigens; apparently none of the sera from adult patients recognized all of the variants presented
— id: 45580, year: 1989, vol: 83, page: 464, stat: Journal Article,

New approaches to the serotypic analysis of the epidemiology of Plasmodium falciparum
Forsyth KP; Anders RF; Kemp DJ; Alpers MP
1988 Oct 31;321(1207):485-493, Philosophical transactions of the Royal Society of London. Series B. Biological sciences
Considerable antigenic heterogeneity of Plasmodium falciparum has been demonstrated in natural parasite populations. However, very little is known about the relative virulence, transmission efficiency and prevalence over space and time of parasites expressing different serotypes of variant antigens. The recent application of recombinant DNA techniques to express a wide range of P. falciparum antigens in Escherichia coli has led to a better understanding of the molecular basis of antigenic diversity of a number of parasite proteins including the precursor to the major merozoite surface antigen (PMMSA) and the heat-stable S-antigens. Highly specific reagents such as DNA probes, monoclonal antibodies and polyclonal antisera to either cloned antigens or synthetic peptides have become available for serotypic analysis of natural parasite populations. With these reagents important epidemiological questions can now be asked concerning the population biology of different serotypes of P. falciparum. The use of the polymorphic S-antigen system as a serotypic marker to analyse the transmission dynamics of P. falciparum in Madang, Papua New Guinea (PNG) is discussed. Results of serotyping studies with the S-antigen system highlight the complexities of malaria transmission, which require consideration in the design of malaria vaccine trials
— id: 45582, year: 1988, vol: 321, page: 485, stat: Journal Article,

Identification of phosphorylcholine epitope-containing antigens in Brugia malayi and relation of serum epitope levels to infection status of jirds with brugian filariasis
Wenger JD; Forsyth KP; Kazura JW
1988 Jan;38(1):133-141, American journal of tropical medicine & hygiene
The Gib 13 monoclonal antibody was raised against eggs of Onchocerca gibsoni and subsequently found to react with a phosphorylcholine epitope designated as the T15 idiotype. Since an immunoradiometric assay based on the Gib 13 monoclonal antibody holds promise for serodiagnosis of filariasis, the goals of the current study were to evaluate phosphorylcholine epitope production and release by various parasite stages and to assess changes in serum epitope levels during different phases of Brugia malayi infection in jirds. Extracts of B. malayi adult male worms, female worms, and microfilariae contained Gib 13 monoclonal antibody-reactive antigens of Mr 25-30,000, 57-90,000, and approximately equal to 200,000. Adult female worms secreted ten-fold more epitope than microfilariae on a weight basis. Phosphorylcholine-containing antigens were localized in female and male worms, respectively, in egg-bearing regions and the intestines. Assessment of the relationship between serum levels of Gib 13 antibody-binding epitope and parasitologic status of B. malayi-infected jirds showed that the immunoradiometric assay distinguishes patent infected from uninfected control animals, detects a significant rise in epitope level during the prepatent phase of infection, and is unaffected by diethylcarbamazine-induced reduction in the intensity of microfilaremia. There was a direct positive correlation between serum epitope level and female adult worm load. Quantification of serum phosphorylcholine epitope of the T15 idiotype may be useful as an indirect measure of parasite burden in humans with lymphatic filariasis that is independent of microfilaremia
— id: 45583, year: 1988, vol: 38, page: 133, stat: Journal Article,

New approaches to the control of lymphatic filariasis using diethylcarbamazine
Forsyth, K
1987 Sep;30(3):189-191, Papua & New Guinea medical journal
— id: 70792, year: 1987, vol: 30, page: 189, stat: Journal Article,

Epidemiology of human T cell leukemia virus type I infection in East Sepik Province, Papua New Guinea
Kazura, J W; Saxinger, W C; Wenger, J; Forsyth, K; Lederman, M M; Gillespie, J A; Carpenter, C C; Alpers, M A
1987 Jun;155(6):1100-1107, Journal of infectious diseases
A serological survey of 317 healthy residents of rural Papua New Guinea (PNG) showed a 26% prevalence of antibodies to human T cell leukemia virus type I (HTLV-I). Antibody to HTLV-I was detected in 16% of children less than or equal to 10 years old (including an 18-month-old child) and increased to greater than or equal to 24% in subjects greater than 20 years old. Prospective examination for antibody in 104 residents of one village revealed a seroconversion rate of 13% over a one-year period. The mean titer of antibody in these subjects (1:183) was lower (P less than .0005) than that in persons who were persistently seropositive (1:718). Analysis for clustering of infected subjects suggested that personal contact within the home played a role in the horizontal spread of HTLV-I. These data indicate that HTLV-I infection has a higher prevalence in PNG than in other endemic parts of the world, exposure occurs at an early age, and infection and/or seroconversion is common in adults as well as in children
— id: 70788, year: 1987, vol: 155, page: 1100, stat: Journal Article,

Chromosome size polymorphisms in Plasmodium falciparum can involve deletions and are frequent in natural parasite populations
Corcoran LM; Forsyth KP; Bianco AE; Brown GV; Kemp DJ
1986 Jan 17;44(1):87-95, Cell
A comparison of independent cultured isolates of Plasmodium falciparum revealed that while chromosome number was constant, the sizes of analogous chromosomes varied widely. We show here that chromosome size polymorphisms are not generated during differentiation of the asexual blood stages, as the molecular karyotype of a cloned parasite line is constant through this part of the life cycle. Experiments using whole P. falciparum chromosomes as hybridization probes to examine polymorphisms within two independent parasite populations indicate that the polymorphisms observed here are not the consequence of large-scale interchromosomal exchanges, and imply that deletions/duplications represent one mode of generating chromosome length polymorphisms. Although the deletions probably involve repetitive DNA, we show here that structural genes for P. falciparum antigens can also be lost. Furthermore, these dramatic size polymorphisms occur not only in cultured lines of P. falciparum, but with surprising frequency in natural malarial infections
— id: 45584, year: 1986, vol: 44, page: 87, stat: Journal Article,

Antigen detection assays in filariasis : diagnosis of infection and evaluation of control measures
Forsyth KP; Mitchell GF
Nuclear medicine and related radionuclide applications in developing countries : proceedings of an International Viena : International Atomic Energy Agency (UNIPUB), 1986,
— id: 4234, year: 1986, vol: , page: 111, stat: Chapter,

Differential recognition of a protective filarial antigen by antibodies from humans with bancroftian filariasis
Kazura, J W; Cicirello, H; Forsyth, K
1986 Jun;77(6):1985-1992, Journal of clinical investigation
The objectives of this study were to identify filarial antigens which induce enhanced clearance of circulating microfilariae and to establish if human antibody reactivity with these molecules correlates with the apparent parasite burdens of residents of an endemic area of Bancroftian filariasis. Mice immunized with an extract of Brugia malayi microfilariae develop IgG antibodies to four major filarial antigens with an apparent molecular weight (Mr) of approximately 112,000, 60,000, 45,000, and 25,000. Animals immunized with gel slices containing the approximately 25,000-Mr antigen are resistant to intravenous challenge with live microfilariae (78-98% reduction in parasitemia vs. controls, P less than 0.01). A group of 22 amicrofilaremic humans had a significantly higher (P less than 0.025) mean antibody titer to the Mr 25,000-Mr antigen (1: 424) than 16 microfilaremic individuals (1:95). There were no significant differences between the two groups in antibody titers to filarial antigens of Mr approximately 112,000, 60,000, and 45,000 Mr. These data suggest that a high degree of reactivity to the 25,000-Mr antigen in humans with lymphatic filariasis correlates with a parasitologic status that is least conducive to transmission of infection
— id: 70789, year: 1986, vol: 77, page: 1985, stat: Journal Article,

Detection of serum antibodies and circulating antigens in a chimpanzee experimentally infected with Onchocerca volvulus
Weiss, N; van Den Ende, M C; Albiez, E J; Barbiero, V K; Forsyth, K; Prince, A M
1986 ;80(4):587-591, Transactions of the Royal Society of Tropical Medicine & Hygiene
The course of the humoral immune response was followed in a chimpanzee experimentally infected over 27 weeks with a total of 168 Onchocerca volvulus 3rd-stage larvae obtained from naturally infected wild-caught blackflies. Antibodies against an adult worm extract could be detected by ELISA from week 16 onwards (after the inoculation of 44 larvae). Peak antibody levels were observed between weeks 66 and 74 (about one year after the last larval injection). Thereafter, antibody levels markedly decreased but rose again after week 120. First microfilariae could be detected from week 124 onwards. Microfilarial counts remained low (not more than two microfilariae per skin snip) until the end of the observation period. High levels of IgM antibodies against adult O. volvulus antigens were detectable between weeks 26 and 80 by ELISA. Total IgE levels were found to be only marginally elevated during the course of the infection. Circulating parasite antigens were only detectable for a short time (weeks 34 to 44) of the prepatent period by immuno-radiometric assays (IRMAs) using monoclonal antibodies which were raised against O. gibsoni eggs. Competitive radio-immuno-assays detected host antibodies inhibiting binding of 125I-labelled monoclonal antibodies to parasite antigens from week 28 onwards. Host antibodies clearly interfere later in infection with the detection of circulating antigens
— id: 70791, year: 1986, vol: 80, page: 587, stat: Journal Article,

A monoclonal antibody-based immunoradiometric assay for detection of circulating antigen in Bancroftian filariasis
Forsyth KP; Spark R; Kazura J; Brown GV; Peters P; Heywood P; Dissanayake S; Mitchell GF
1985 Feb;134(2):1172-1177, Journal of immunology
A monoclonal antibody designated Gib 13 has been used in an immunoradiometric assay (IRMA) to detect circulating antigen in the sera of Wuchereria bancrofti-infected subjects from an endemic area of Papua New Guinea. A clear association between the presence of patent infection and the Gib 13 target epitope in serum was established because 93% of microfilaremic individuals were antigen-positive. Moreover, there was a significant correlation between levels of serum antigen and blood microfilarial counts. Detection of circulating antigen in amicrofilaremic subjects with acute symptoms of lymphatic filariasis, and 53% of asymptomatic amicrofilaremic subjects, but not in nonendemic controls, suggests that the Gib 13 IRMA will also be of value in the diagnosis of occult filariasis. However, as in all IRMA based on detection of potentially immunogenic molecules in man, antibodies can be expected to be the major contributor to reduced sensitivity of the assay
— id: 45585, year: 1985, vol: 134, page: 1172, stat: Journal Article,

Detection of circulating antigen in bancroftian filariasis by using a monoclonal antibody
Dissanayake S; Forsyth KP; Ismail MM; Mitchell GF
1984 Nov;33(6):1130-1140, American journal of tropical medicine & hygiene
A monoclonal antibody designated Gib 13-5-2 (Gib 13) and directed against the cattle parasite Onchocerca gibsoni was used in a two-site immunoradiometric assay (IRMA) for detection of circulating antigen in the sera of Wuchereria bancrofti-infected individuals from Sri Lanka and Papua New Guinea. The microfilaremic patients were, in general, serum antigen positive by the Gib 13 IRMA. Among the amicrofilaremic patients, 47% of those with lymphedema, lymphangitis, hydrocele, etc., and 25% of those with elephantiasis had circulating antigen. Correlation of the presence of serum antigen with clinical status indicated that the Gib 13 target antigen in serum is probably an indicator of either active or early infection, or of both. The antigen was also detected in the urine of some patients. By sodium dodecyl sulphate polyacrylamide gel electrophoresis immunoblotting, Gib 13 target antigens of molecular weights 67,000 and 52,000 were identified
— id: 45586, year: 1984, vol: 33, page: 1130, stat: Journal Article,

Differences in the surface radioiodinated proteins of skin and uterine microfilariae of Onchocerca gibsoni
Forsyth KP; Copeman DB; Mitchell GF
1984 Feb;10(2):217-229, Molecular & biochemical parasitology
Surface labeling studies using two populations of Onchocerca gibsoni microfilariae revealed important differences in major radioiodinated proteins. Small numbers of microfilariae harvested from the skin of cattle or the uteri of adult worms from skin nodules were purified, radioiodinated, solubilized and the proteins analysed by two dimensional gel electrophoresis and autoradiography. As reported previously, uterine microfilariae showed a complex profile of radioiodinated proteins, none of which appeared to be bovine albumin or immunoglobulin. In contrast, application of the same techniques to skin microfilariae demonstrated only one major labeled protein complex of approximate Mr 67 000. This protein complex was immunoprecipitated with an antiserum to bovine serum albumin. Surprisingly, fluorescence techniques failed to show bovine serum albumin on the surface of living microfilariae. Although the evidence is circumstantial at present, acquisition of host albumin (perhaps oriented in a particular way) may be a means whereby skin microfilariae evade immune effector mechanisms and, when living, generally fail to elicit inflammatory reactions in the skin of the host
— id: 45588, year: 1984, vol: 10, page: 217, stat: Journal Article,

Onchocerca gibsoni: increase of circulating egg antigen with chemotherapy in bovines
Forsyth KP; Mitchell GF; Copeman DB
1984 Aug;58(1):41-55, Experimental parasitology
Monoclonal antibodies directed to stage-specific surface antigens of Onchocerca gibsoni eggs were used in immunoradiometric assays to detect antigens in the sera of cattle infected with O. gibsoni. Two monoclonal antibodies detected antigens, presumably of egg origin, in sera. The target antigens appeared to be carbohydrate in nature and of variable molecular weights. Significant increases in levels of circulating egg antigens were found after treatment of infected cattle with benzimidazole compounds. These drugs cause disruption of embryogenesis and accelerated loss of worm uterine contents. In contrast, administration of either macrofilaricides or microfilaricides to infected cattle did not alter pretreatment levels of circulating egg antigens. Measurement of changes in levels of circulating antigens by immunoradiometric assays with stage-specific monoclonal antibodies provides a new means of assessing the efficacy of drugs and their site of action in onchocerciasis
— id: 45587, year: 1984, vol: 58, page: 41, stat: Journal Article,

Parasitologic and clinical features of bancroftian filariasis in a community in East Sepik Province, Papua New Guinea
Kazura, J W; Spark, R; Forsyth, K; Brown, G; Heywood, P; Peters, P; Alpers, M
1984 Nov;33(6):1119-1123, American journal of tropical medicine & hygiene
Bancroftian filariasis has been reported in several areas of Papua New Guinea. The epidemiologic features and natural history of Wuchereria bancrofti infection in this geographic region, however, have not been well-defined. The objective of this study was to assess the parasitological and clinical features of bancroftian filariasis in a community in East Sepik Province, Papua New Guinea. In a village of 99 individuals, the overall prevalence of microfilaremia was 68%. The microfilarial carrier rate was high in those less than or equal to 10 years (62%), remained elevated in the 11-20, 21-30, and 31-40 age groups (42-55%), and peaked in subjects greater than or equal to 41 years old (90%). The geometric mean level of parasitemia in all subjects with patent infection was 3,198 microfilariae/ml blood. This value was 78 parasites/ml in the less than or equal to 10-year-old age group, increased to 1,753 in 21 to 30-year-olds and was markedly elevated in subjects greater than or equal to 41 years old (6, 792 microfilariae/ml). Acute symptoms of filariasis (lymphadenitis and lymphangitis) were initially noted in individuals between the ages of 11 and 20 years (30%). Obstructive disease, manifested as elephantiasis and hydroceles, was present in 64 and 79% of 31-40 and greater than or equal to 41-year-olds, respectively. These data suggest that intense transmission of W. bancrofti infection occurs at an early age in this area of East Sepik Province; patent infection remains high in older age groups. Irreversible lymphatic obstruction develops 20-30 years after initial infection and may be associated with either amicrofilaremia or microfilaremia
— id: 70790, year: 1984, vol: 33, page: 1119, stat: Journal Article,

Purification of Onchocerca gibsoni microfilariae
Forsyth KP; Copeman DB; Mitchell GF
1982 Feb;12(1):53-57, International journal for parasitology
— id: 45589, year: 1982, vol: 12, page: 53, stat: Journal Article,

Analysis of infection characteristics and antiparasite immune responses in resistant compared with susceptible hosts
Mitchell GF; Anders RF; Brown GV; Handman E; Roberts-Thomson IC; Chapman CB; Forsyth KP; Kahl LP; Cruise KM
1982 ;61(1):137-188, Immunological reviews
— id: 45590, year: 1982, vol: 61, page: 137, stat: Journal Article,

Identification of radioiodinated cuticular proteins and antigens of Onchocerca gibsoni microfilariae
Forsyth KP; Copeman DB; Abbot AP; Anders RF; Mitchell GF
1981 Sep;38(3):329-342, Acta tropica
The filarial parasite of cattle, Onchocerca gibsoni, has been used to establish procedures of antigen identification with a view of applying these techniques to studies on human filarial parasites. Emphasis has been placed on methods suitable for use with small numbers of parasites. Microfilariae (mf) of O. gibsoni were extracted from nodular worms, purified and 125I-labeled using IODO-GEN in solid-phase. Radioactivity was shown to be confined to the cuticle of sectioned mf using the technique of electronmicroscope autoradiography. Radiolabeled mf were analysed by two-dimensional gel electrophoresis. Autoradiographs of 125I-labeled proteins of O. gibsoni mf were relatively complex, there being at least 32 proteins ranging in molecular weights from 20,000 to 120,000 and displaying considerable charge heterogeneity. Evidence was obtained that at least the major serum proteins of the host, albumin or immunoglobulin, were not absorbed on the surface of these uterine mf and detectable in the labeled surface protein patterns. Sera from infected cattle immunoprecipitated 5 labeled proteins from a Triton X-100 extract of 125I-labeled mf. Sera from either of two calves which had been given multiple injections of mf subcutaneously, and which had no detectable skin mf, recognised 6 additional proteins in this extract as well as 3 of the proteins recognised by sera from infected cattle
— id: 45592, year: 1981, vol: 38, page: 329, stat: Journal Article,

The major radioiodinated cuticular antigens of Onchocerca gibsoni microfilariae are neither species nor onchocerca specific
Forsyth KP; Copeman DB; Anders RF; Mitchell GF
1981 Sep;38(3):343-352, Acta tropica
The possible role of microfilarial surface (cuticular) antigens in immuno-diagnosis of human filarial infections has been assessed using microfilariae (mf) of the cattle parasite Onchocerca gibsoni. A Triton X-100 extract of 125I-labeled O. gibsoni mf was reacted with a panel of sera from humans infected with Onchocerca volvulus, Wuchereria bancrofti and Schistosoma japonicum as well as sera from uninfected controls. Results of these immunoprecipitations indicated that sera from humans infected with O. volvulus or W bancrofti contain antibody specificities recognising certain of the radioiodinated cuticular proteins of O. gibsoni mf. Two-dimensional gel analysis and subsequent autoradiography of these immunoprecipitates showed that 8 radioiodinated proteins recognised by sera from calves injected with O. gibsoni mf were also immunoprecipitated by sera from humans infected with either O. volvulus or W. bancrofti. Thus there appear to be no major radioiodinated cuticular antigens of O. gibsoni mf which are species or onchocerca specific
— id: 45591, year: 1981, vol: 38, page: 343, stat: Journal Article,

Plasmodium berghei: modification of sialic acid on red cells from infected mouse blood
Howard RJ; Day KP
1981 Feb;51(1):95-103, Experimental parasitology
— id: 40155, year: 1981, vol: 51, page: 95, stat: Journal Article,

Accelerated rejection of Nematospiroides dubius intestinal worms in mice sensitized with adult worms
Hurley JC; Day KP; Mitchell GF
1980 Jun;58(3):231-240, Australian journal of experimental biology & medical science
After oral administration of infective third stage larvae (L3) of Nematospiroides dubius to young mice, intestinal worms persist for many weeks. However, in mice injected parenterally with N. dubius adult worms, the intraluminal intestinal infection arising after L3 administration can be terminated within 3 to 4 weeks. This accelerated rejection is seen in sensitized BALB/c mice (and (CBA/H X BALB/c)F1 mice) and in particular females, but has not been demonstrated in sensitized CBA/H mice. In female BALB/c mice, small numbers of living worms are more effective at sensitization than dead worms, intraperitoneal and subcutaneous implantations are both effective, and products from adult worms incubated in vitro (i.e. 'excretory/secretory' (ES) products) will sensitize but only with very high doses in adjuvant. Using appropriate isolated antigen preparations, comparative immunoparasitological analyses in different mice should provide clues on the nature of host-protective immunities against intestinal nematode infections which are potentially chronic. From the present studies, two groups which differ most dramatically in the consequences of adult worm sensitization are young male CBA/H versus older female BALB/c mice
— id: 40156, year: 1980, vol: 58, page: 231, stat: Journal Article,

Studies on chronic versus transient intestinal nematode infections in mice. I. A. comparison of responses to excretory/secretory (ES) products of Nippostrongylus brasiliensis and Nematospiroides dubius worms
Day KP; Howard RJ; Prowse SJ; Chapman CB; Mitchell GF
1979 Autumn;1(3):217-239, Parasite immunology
— id: 40157, year: 1979, vol: 1, page: 217, stat: Journal Article,