A Large Plasmodium vivax Reservoir and Little Population Structure in the South Pacific

Abstract

IntroductionThe importance of Plasmodium vivax in malaria elimination is increasingly being recognized, yet little is known about its population size and population genetic structure in the South Pacific, an area that is the focus of intensified malaria control.MethodsWe have genotyped 13 microsatellite markers in 295 P. vivax isolates from four geographically distinct sites in Papua New Guinea (PNG) and one site from Solomon Islands, representing different transmission intensities.ResultsDiversity was very high with expected heterozygosity values ranging from 0.62 to 0.98 for the different markers. Effective population size was high (12′872 to 19′533 per site). In PNG population structuring was limited with moderate levels of genetic differentiation. F ST values (adjusted for high diversity of markers) were 0.14–0.15. Slightly higher levels were observed between PNG populations and Solomon Islands (F ST = 0.16).ConclusionsLow levels of population structure despite geographical barriers to transmission are in sharp contrast to results from regions of low P. vivax endemicity. Prior to intensification of malaria control programs in the study area, parasite diversity and effective population size remained high.

Uncovering the transmission dynamics ofPlasmodium vivaxusing population genetics

“…67 Furthermore, the lack of population structure in these regions was consistent with high levels of gene flow and a very large effective population size. 3,48 Since these initial surveys however, routine surveillance by the control programme has indicated a 50% reduction in prevalence (I. Mueller, unpublished data). It will be interesting to assess whether this has impacted the parasite population by comparing the population structure at different time points.…”

“…48,50,54,55 Paradoxically, significant multi-locus LD has been observed in some moderate to high transmission settings, 52 which might be explained by serial co-transmission of meiotic recombinants, while in other moderate transmission settings in South-East Asia, no LD was observed. 51 The high diversity of the parasite population even in regions where transmission intensity has declined substantially reflects a large underlying parasite population.…”

“…11,48,50 In the highlands of PNG, transmission is lower and mostly restricted to local outbreaks, yet P. vivax isolates collected during outbreaks still display high diversity, while co-endemic P. falciparum shows a clonal population structure suggesting that low level endemic transmission continues to occur in these regions. 61 In South-East Asia over a billion people are at risk of P. vivax infection.…”

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“…15 This classification defines the accessibility/remoteness of geographic areas based on their road network distance to goods, services and opportunities for social interactions. 16 Study LGAs were classified as either metropolitan, inner regional, or outer regional, remote and very remote.…”

“…15, 16 Of the 715 ASHAs in the district providing newborn care, 438 had received two rounds of training on providing home-based care.…”