Short Report: Gametocytes, Chloroquine Pressure, and the Relative Parasite Survival Advantage of Resistant Strains of Falciparum Malaria in West Africa

Vincent RobertInstitut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Laboratoire de Paludologie, Dakar, Senegal

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Jean-Francois MolezInstitut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Laboratoire de Paludologie, Dakar, Senegal

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Jean-Francois TrapeInstitut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Laboratoire de Paludologie, Dakar, Senegal

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Patients with Plasmodium falciparum infections were selected with an in vivo chloroquine sensitivity assay. Fourteen days after treatment, the gametocytes were studied in relation to asexual parasite responses classified as drug-sensitive or showing RI or RII resistance. Gametocyte prevalence and density appeared significantly higher in RII than RI strains and higher in RI than in sensitive strains. This finding on gametocyte variation in vivo may explain why the RII type of chloroquine resistance has became more prevalent than RI everywhere in tropical Africa in the short time since its emergence. The biological and epidemiologic advantage of chloroquine-resistant malaria mediated through gametocytes is discussed in the context of the present drug pressure in Africa.

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