Studies on the dynamics of transmission of onchocerciasis in a Sudan-savanna area of North Cameroon I

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Abstract
Along the main water courses in the sparsely populated areas of the Sous-Préfecture of Tcholliré, the vectors of onchocerciasis were mainly Simulium damnosum s. str. and S. sirbanum, together with a small proportion of S. squamosum. Over a period of one to three years, vector biting rates were measured at 23 fly-catching sites in the vicinities of nine villages with different endemicities of onchocerciasis. Annual Biting Rates (ABR) on man were estimated as 26 100–83 800 fly-bites per man per year along the rivers Mayo Rey and Vina du Nord, and 11 000–37 400 at rainy season tributaries. Biting rates decreased rapidly at increasing distances from the river, and were between 10 700 and 2400 at 2–10 km crosscountry from the breeding site. Lowest biting rates (50–6000) were measured at the village centres. The ABR varied from year to year in relation to the water-discharge of the main rivers, the coefficient of variation of the mean being 34–49%. The parous rates were 64–73% at the perennial breeding sites and only 17–44% away from the breeding sites, indicating dispersal mainly of young nulliparous flies and a reduced flight-range after oviposition.