CHARACTERISTICS OF PLASMODIUM-FALCIPARUM PARASITES THAT SURVIVE THE LENGTHY DRY SEASON IN EASTERN SUDAN WHERE MALARIA TRANSMISSION IS MARKEDLY SEASONAL

We have examined 83 inhabitants of Asar village in eastern Sudan, wher e malaria transmission lasts approximately 2-3 months each year, for t he presence of Plasmodium falciparum during the prolonged dry season. All patients were treated with a standard dose of chloroquine followin g the first diagnosis, then examined by microscopy and the polymerase chain reaction (PCR) every two weeks for the first two months and subs equently once each month for the next 15 months throughout the dry sea son until the following transmission season. The PCR primers used ampl ified polymorphic regions of the merozoite surface protein-1 (MSP-1), MSP-2, and glutamate-rich protein genes. Results show that subpatent a nd asymptomatic parasitemias persisted in some patients for several mo nths throughout the dry season, often as genetically complex infection s. Different genotypes could coexist together in a single infection an d the proportions of each could fluctuate dramatically during this per iod. However, in some individuals, single genotypes appeared to persis t for several months. Reappearance of clinical symptoms among patients with chronic infections was often associated with appearance of new a lleles, indicating reinfections with parasites of novel genotypes.