MECHANISMS THAT REDUCE TRANSMISSION OF PLASMODIUM-FALCIPARUM MALARIA IN SEMIIMMUNE AND NONIMMUNE PERSONS

Transmission of Plasmodium falciparum can be reduced by immune factors present in the mosquito blood meal. Specific antibodies and white blo od cells (WBCs) can interact with the sexual stages of the parasite in side the mosquito midgut. The relative contribution of serum factors a nd WBCs on transmission reduction in gametocyte carriers from an endem ic area in Cameroon and in travelers with a first malaria experience w as studied. Blood from these gametocyte carriers was fed to mosquitoes through membrane feeders after serum replacement, WBC depiction, or b oth. In most imported malaria cases, serum factors, WBCs, or both show ed a significant effect on transmission reduction, while infectiousnes s of gametocyte carriers from Cameroon was reduced by humoral plasma f actors only. In addition, the infectivity of gametocytes from semiimmu ne carriers was significantly lower compared with that of nonimmune ca rriers, and infectivity was independent of gametocyte density and the presence of WBCs or plasma factors (or both) in the blood meal.