The Onchocerca volvulus transmission potentials and associated patterns of onchocerciasis at four Cameroon Sudan-savanna villages

Abstract

The intensity of O. volvulus infection, and the prevalence of certain eye lesions and of blindness, are compared in 4 hyperendemic Cameroon Sudan-savanna villages. The pattern of the disease is related to the annual transmission potentials to which the communities were exposed, and the results are compared with those obtained previously in forest villages. The prevalence and intensity of O. volvulus infections in S. damnosun were more closely related to the prevalence of positive skin snip than to the mean concentrations of microfilariae in the skin. Owing to the differential dispersal of nulliparous and parous flies in savanna, the annual transmission potentials were related more closely to the numbers of parous flies than to the total fly population. Factors governing the exposure of persons to infective flies are discussed. Seasonal transmission, which was usually light, did not lead to severe onchocerciasis; the more perennial the transmission the heavier was its degree, and the more prevalent were eye lesions and blindness. Annual transmission potentials of about 500, 1750, 1800+ and 2900 were associated with an increase in the mean intensity of infection and in the prevalence of eye lesions, while the onchocerciasis blindness rate in persons over 20 years old rose from nil to 3.3, 9.2 and 10 per cent respectively. Annual transmission potentials of 4400 and 19000 were recorded on the banks of S. damnosum breeding rivers in the area, but no villages were sited at such places and it is probable that no community could survive under such conditions. The bearing of these findings on the anticipated effects of S. damnosum control operations in savanna is discussed.