Abstract
BackgroundMalaria parasite population genetic structure varies among areas of differing endemicity, but this has not been systematically studied across Plasmodium falciparum populations in Africa where most infections occur.MethodsTen polymorphic P. falciparum microsatellite loci were genotyped in 268 infections from eight locations in four West African countries (Republic of Guinea, Guinea Bissau, The Gambia and Senegal), spanning a highly endemic forested region in the south to a low endemic Sahelian region in the north. Analysis was performed on proportions of mixed genotype infections, genotypic diversity among isolates, multilocus standardized index of association, and inter-population differentiation.ResultsEach location had similar levels of pairwise genotypic diversity among isolates, although there were many more mixed parasite genotype infections in the south. Apart from a few isolates that were virtually identical, the multilocus index of association was not significant in any population. Genetic differentiation between populations was low (most pairwise FST values < 0.03), and an overall test for isolation by distance was not significant.ConclusionsAlthough proportions of mixed genotype infections varied with endemicity as expected, population genetic structure was similar across the diverse sites. Very substantial reduction in transmission would be needed to cause fragmented or epidemic sub-structure in this region.
Highlights
Malaria parasite population genetic structure varies among areas of differing endemicity, but this has not been systematically studied across Plasmodium falciparum populations in Africa where most infections occur
When human malaria infections contain a mixture of multiple haploid parasite clones, genetically different gametocytes may be taken into a mosquito blood meal, leading to heterozygous diploid
In the Republic of Guinea, 105 filter-paper blood samples were collected from patients presenting with malaria between December 2009 and February 2010 who were positive for malaria parasites by rapid diagnostic test (RDT) and slide examination at the Government Health Centres in Boke, N’Zerekore and Forecariah
Summary
Malaria parasite population genetic structure varies among areas of differing endemicity, but this has not been systematically studied across Plasmodium falciparum populations in Africa where most infections occur. Microsatellite surveys of P. falciparum from endemic populations have clearly shown that infections are less genotypically mixed in areas of low transmission, which does apparently reduce the effective recombination rate and allow linkage disequilibrium to persist locally [8]. Such a pattern occurs in many populations in South America and Southeast Asia, and a wide spectrum of population structures can be seen among different sites within individual countries such as Brazil [9], Malaysia [10], Thailand [8,11,12], Philippines [13], and Papua New Guinea [8,14]. Such changes may have started to affect parasite population genetics, an understanding of which is needed for considering potential elimination or sustained endemic control
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