Epidemiological studies of onchocerciasis in savanna villages of Sierra Leone

The overall prevalence of onchocerciasis was 78% and 73% in three villages of the woodland savanna of Koinadugu and four villages of the savanna-forest mosaic of Kambia respectively. The total number of persons examined was 611. In Koinadugu the prevalence of microfilariae of Onchocerca volvulus in skin snips from the iliac crest and canthus was 51.3% and 22.5% respectively while corresponding figures for Kambia were 52.2% and 19.3%. The pattern of clinical manifestations were similar in both districts, the overall rates for nodules, skin lesions (moderate and severe) and leg elephantiasis being 53.2%, 12.5% and 0.3% respectively. No cases of hanging groin were seen. The prevalence of onchocercal eye lesions was lower in the present surveys than in our own findings in Guinea or the findings of other investigators in the Guinea or Sudan savanna of West Africa. In the present study prevalences of the fourmain blinding eye lesions in persons aged 30 years or more were sclerosing keratitis (3.7%), iritis (8.7%), optic atrophy (14.2%) and choroidoretinitis (11.3%), and the prevalence of blindness was 4.2% (both eyes) and 2.0% (one eye). Males were more commonly affected than females. Further entomological studies are needed to elucidate the relative role played by the different cytospecies of Simulium damnosum s.l. in the transmission of onchocerciasis in the savanna of Sierra Leone.