Onchocerciasis infection in children born during 14 years of Simulium control in West Africa.

The incidence of onchocerciasis infection in children born since the start of vector control is one of the indicators used in the epidemiological evaluation of the Onchocerciasis Control Programme in West Africa (OCP). Though initially of littel value, after a decade of control it has become a sensitive indicator of residual transmission. The results of 14 years of control are reported. In 179 villages parasitological surveys were undertaken at intervals of 3-4 years. 15,286 children were examined and 110 were found to be infected, compared to an expected number of 2467 infected had there been no control. There was considerable geographical variation in the results. In the large central OCP area the results were excellent. Of 12,172 children examined in 127 villages, only 23 were found to be infected compared to an expected number of 1960 without control. This suggests that larviciding had achieved a 99% reduction in the incidence of infection in children. Additional surveys in 2 foci in the central OCP area where transmission had relapsed showed that these problems were very localized. Most villages with infected children were found in OCP border areas in the east and west, which had been reinvaded by infective vectors from elsewhere, and in the intermediate area between forest and savanna in Côte d'Ivoire where there had been partial control failures because of resistance. The incidence of infection in children was reduced by an estimated 68% in the eastern reinvaded area, by 87% in the western reinvaded area, and by 84% in the intermediate area.