The differing impact of chloroquine and pyrimethamine/sulfadoxine upon the infectivity of malaria species to the mosquito vector.

B HoghDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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A Gamage-MendisDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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G A ButcherDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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R ThompsonDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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K BegtrupDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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C MendisDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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S M EnosseDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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M DgedgeDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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J BarretoDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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W ElingDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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R E SindenDepartment of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen.

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Using serum or infected blood from Danish volunteers and Plasmodium falciparum-infected Mozambican patients, respectively, the impact of curative doses of chloroquine and pyrimethamine/sulfadoxine upon infectivity of P. falciparum to Anopheles arabiensis and An. gambiae or of P. berghei to An. stephensi was studied. Both treatments cleared circulating P. falciparum gametocytes within 28 days. Before this clearance, chloroquine enhanced infectivity to An. arabiensis, whereas pyrimethamine/sulfadoxine decreased infectivity. Patients harboring chloroquine-resistant parasites as opposed to -sensitive ones were 4.4 times more likely to have gametocytes following treatment. In contrast, pyrimethamine/sulfadoxine-resistant parasites were 1.9 times less likely to produce gametocytes. In laboratory infections using replicated P. berghei or P. falciparum preparations, serum from chloroquine-treated, uninfected, nonimmune volunteers enhanced gametocyte infectivity with increasing efficiency for 21 days following treatment, whereas pyrimethamine/sulfadoxine significantly suppressed infectivity. The observed enhancement in infectivity induced by the use of chloroquine combined with increased gametocytemias in chloroquine-resistant strains may in part explain the rapid spread of chloroquine resistance in endemic populations.

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