THE DIFFERING IMPACT OF CHLOROQUINE AND PYRIMETHAMINE SULFADOXINE UPON THE INFECTIVITY OF MALARIA SPECIES TO THE MOSQUITO VECTOR/

Using serum or infected blood from Danish volunteers and Plasmodium fa lciparum-infected Mozambican patients, respectively, the impact of cur ative doses of chloroquine and pyrimethamine/sulfadoxine upon infectiv ity of P. falciparum to Anopheles arabiensis and An. gambiae or of P. berghei to An. stephensi was studied. Both treatments cleared circulat ing P. falciparum gametocytes within 28 days. Before this clearance, c hloroquine enhanced infectivity to An. arabiensis, whereas pyrimethami ne/sulfadoxine decreased infectivity. Patients harboring chloroquine-r esistant parasites as opposed to -sensitive ones were 4.4 times more l ikely to have gametocytes following treatment. In contrast, pyrimetham ine/sulfadoxine-resistant parasites were 1.9 times less likely to prod uce gametocytes. In laboratory infections using replicated P. berghei or P. falciparum preparations, serum from chloroquine-treated, uninfec ted, nonimmune volunteers enhanced gametocyte infectivity with increas ing efficiency for 21 days following treatment, whereas pyrimethamine/ sulfadoxine significantly suppressed infectivity. The observed enhance ment in infectivity induced by the use of chloroquine combined with in creased gametocytemias in chloroquine-resistant strains may in part ex plain the rapid spread of chloroquine resistance in endemic population s.