Population dynamics of Plasmodium falciparum in an unstable malaria area of eastern Sudan

The Plasmodium falciparum population in Asar village, eastern Sudan, where malaria transmission is markedly seasonal, was monitored monthly over a per iod of 15 months. A cohort of infected patients was treated and then follow ed monthly throughout the dry season until the next transmission season. Pa rasitaemia detected by microscopy among the cohort reduced dramatically fol lowing treatment, but remained sporadic during the dry season, and reappear ed following the onset of the next wet season. However between 40 and 50 % of the cohort retained a persisting parasitaemia detectable by PCR througho ut the dry season. These parasites mere genetically complex, consisting of multiple clones with a large repertoire of alleles of the studied genes. Wh ile the number of clones per host dropped significantly following treatment of acute cases during the transmission season, drug treated people neverth eless maintained an average of one clone throughout the dry season. Allele frequencies of MSP-1, MSP-2 and GLURP showed slight, statistically insignif icant, fluctuations between the dry and wet seasons. A higher frequency of inbreeding was estimated among the parasites that survived the dry season c ompared to the wet season.