Artesunate reduces but does not prevent posttreatment transmission of Plasmodium falciparum to Anopheles gambiae

Combination therapy that includes artemisinin derivatives cures most falcip arum malaria infections. Lowering transmission by reducing gametocyte infec tivity would be an additional benefit. To examine the effect of such therap y on transmission, Gambian children with Plasmodium falciparum malaria were treated with standard regimens of chloroquine or pyrimethamine-sulfadoxine alone or in combination with 1 or 3 doses of artesunate. The infectivity t o mosquitoes of gametocytes in peripheral blood was determined 4 or 7 days after treatment. Infection of mosquitoes was observed in all treatment grou ps and was positively associated with gametocyte density. The probability o f transmission was lowest in those who received pyrimethamine-sulfadoxine a nd 3 doses of artesunate, and it was 8-fold higher in the group that receiv ed pyrimethamine-sulfadoxine alone. Artesunate reduced posttreatment infect ivity dramatically but did not abolish it completely. The study raises ques tions about any policy to use pyrimethamine-sulfadoxine alone as the first- line treatment for malaria.