A cohort study of Plasmodium falciparum diversity during the dry season inNdiop, a Senegalese village with seasonal, mesoendemic malaria

Prolonged carriage of Plasmodium falciparum in humans during the dry season is critical for parasite survival, as the infected subjects constitute a m ajor reservoir in the absence of transmission. Yet, very little is known ab out the host/parasite interactions contributing to parasite persistence. In order to study the characteristics of P. falciparum infections during the dry season, we have genotyped parasites collected from untreated, asymptoma tic individuals during 3 cross-sectional surveys conducted during the dry s eason in Ndiop, a Senegalese village with seasonal, mesoendemic malaria. Mo nthly entomological surveillance did not detect any transmission during tha t period. Parasite prevalence decreased markedly in the children aged < 7 y ears after 7 months of undetected transmission, but was stable in older chi ldren and adults throughout the dry season. In all chronically infected ind ividuals, infection complexity remained stable, but there were substantial fluctuations of individual genotype(s), reflecting complex dynamics of mult iple-clone infections during chronic asymptomatic parasite carriage. This f luctuation resulted in changes in the msp1 and msp2 allelic distribution wi thin the cohort after 7 months of undetected transmission, contrasting with the stability observed during the preceding rainy season in that village.