Effect of the Sickle Cell Trait Status of Gametocyte Carriers of Plasmodium falciparum on Infectivity to Anophelines

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  • Institut Francais de Recherche Scientifique pour le Developpement en Cooperation (ORSTOM), Organisation de Coordination pour la lutte contre les Grandes Endemies en Afrique Centrale, University of Yaounde 1, Ministere de la Recherche Scientifique et Technique, Institute of Medical Microbiology, University of Nijmegen, Division of Hematology, Albert Einstein College of Medicine, Yaounde, Cameroon
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Insect-reared Anopheles gambiae were experimentally fed with the blood of naturally infected human volunteers carrying gametocytes of Plasmodium falciparum. Infection of at least one mosquito was successful in 86 experiments. For these gametocyte carriers, the hemoglobin types studied were AA (normal, n = 77), AS (heterozygous sickle cell, n = 8), and SS (homozygous sickle cell, n = 1). The mean of the percentages of infected mosquitoes by gametocyte carriers of AS hemoglobin was almost double that of carriers of AA: 30.4% versus 17.5%. The genetic protection in humans conferred by the βs gene in its heterozygous form seems to be associated with an increasing effect on P. falciparum transmission from humans to mosquitoes. The epidemiologic and evolutionary aspects of this finding are discussed.