High Human Malarial Infectivity to Laboratory-Bred Anopheles gambiae in a Village in Burkina Faso

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  • ORSTOM, Centre Muraz, Bobo-Dioulasso, Burkina Faso, Universite J. Fourrier, Paris, France

The malarial infectivity of an African village population was tested by selecting a demographically representative sample of individuals for study, regardless of parasitemia or gametocytemia. The infectivity of this population people to laboratory-bred mosquitoes was investigated using membrane feeding techniques. Tests on 322 subjects (greater than four years of age) indicated that approximately 48.4% were capable of infecting mosquitoes. There were similar proportions of infectious individuals among gametocyte carriers (52.5%) and nongametocyte carriers (46.6%). All age groups appeared to contribute equally to this infective reservoir. Most of the infections resulted in low oocyst loads (1.8 oocysts) on the midgut of the positive mosquitoes and only a few mosquitoes per batch were infected (11.5%). A previous entomologic survey estimated 90 infected bites/person/year and a low parity index in Anopheles gambiae (< 60%) as well as in An. funestus (< 40%), the two main malaria vectors in this region. This low parity index could indicate a low life expectancy for infected mosquitoes and could therefore explain an inoculation rate lower than expected considering the high degree of infectivity of the human population studied.