Gametocytemia and infectivity to mosquitoes of patients with uncomplicatedPlasmodium falciparum malaria attacks treated with chloroquine or sulfadoxine plus pyrimethamine

Plasmodium falciparum gametocytemia and its related infectivity for mosquit oes was studied in 115 patients (median age = 18 years, range = 4-45) with simple malaria attacks who lived in the hypoendemic area of Dakar, Senegal. Patients were included in a 28-day in vivo sensitivity test after treatmen t with chloroquine (CQ, n = 82) or sulfadoxine plus pyrimethamine (SP, n = 33). The prevalence of resistant infections was 58.5% in those treated with CQ and 0% in those heated with SP. The gametocytemia peaked at day 7 after treatment. The maximal gametocyte prevalence was 38.2% in the CQ-sensitive infection group, 89.6% in the CQ-resistant group, and 97.0% in those treat ed with SP. The maximal geometric mean gametocytemia was 2.19/mu l in the C Q-sensitive infection group, 29.12/mu l in the CQ-resistant group and 85.55 /mu l in those treated with SP. The period between appearance of the first clinical symptom and treatment was positively related to gametocyte prevale nce at days 0 and 2. Experimental infection of wild Anopheles arabiensis us ing membrane feeders was performed at days 0 and 7, and mosquito infectivit y was measured by oocyst detection on the midgut. At day 0, 14.1% of the pa tients had infected at least 1 mosquito, and at day 7, this value was 38.5% . The mean percentage of infected mosquitoes was 3.2% at day 0 and 12.6% at day 7. At day 7 after treatment with CQ, the relative risk for patients wi th resistant infections of infecting anophelines was 4.07 higher than in th ose with sensitive infections. No difference was observed in infectivity fo r mosquitoes between RI-type resistance and the RII + RIII-type resistance. A sporonticidal effect of SP was observed at day 7 after treatment. These data show that P. falciparum gametocytes and their infectivity for mosquito es were differentiated according to the drug used, its efficacy, and the du ration of symptoms before treatment; they were not dependent on the density of asexual stages. Prompt treatment of malaria cases performed at the begi nning of symptoms could limit the spread of resistant parasites.