Partner study description

The dry season in The Gambia presents a bottleneck for the total parasite population as there is little or no malaria transmission. Some individuals maintain a malaria infection through this period, usually at very low densities, without having any symptoms, and are the source from which the transmission restarts the following season. In this study, Antoine Claessens and his colleagues from the MRC Unit The Gambia at the London School of Hygiene and Tropical Medicine aim to test the hypothesis that some Plasmodium falciparum “strains” are more likely to survive the ~8 month long dry season. More specifically, the frequency of alleles conferring dry season growth advantage will be high in June but lower towards the end of the transmission season in December. In practice, fingerpick and veinous blood samples are collected every three months from ~1000 participants in a village in the eastern part of The Gambia. All blood samples are filtered through a cellulose column to remove white blood cells. P. falciparum status is determined by nested-PCR or qPCR. All P. falciparum positive samples are shipped to the Wellcome Sanger Institute for whole genome sequencing, after a DNA amplification step. This work will provide important information for the possible elimination of malaria in The Gambia, as the last remaining parasites are likely to show a similar phenotype of infection to parasites in the dry season (low parasitaemia and asymptomatic, i.e. “the last parasite standing is the strongest” hypothesis).