Onchocerciasis in Sierra Leone I. Studies on the prevalence and transmission at Gbaiima village

A longitudinal survey — parasitological, clinical, immunological and entomological — of onchocerciasis is being conducted in Gbaiima village in Sierra Leone. The estimated Annual Transmission Potential (ATP) is 5863. More than 80% of the annual transmission occurs between October and December. Four species of the Simulium damnosum complex are known to breed in a nearby river. The relative role of these species as vectors has yet to be determined. The total population (598 persons) aged one year and over were examined. Based on microfilarial and nodular rates the prevalence of onchocerciasis was 68·6%. In persons above 15 years of age this prevalence was 88·9%. Microfilarial and nodular rates were related to age. Severe skin lesions occurred in 1·0% of persons. 24 adults (7·5%) were blind (but the cause of the blindness was not determined).