Onchocerciasis in Sierra Leone 2: a comparison of forest and savanna villages

Abstract

Very little of the original primary forest remains in Sierra Leone and the savanna is mainly woodland or a forest-savanna mosaic. The prevalence of microfilariae of Onchocerca volvulus, nodules and moderate or severe skin lesions was higher in forest than savanna villages. In forest villages the prevalence of microfilariae was 71.8% at the iliac crest, 36.6% (outer canthus), 12.8% (cornea) and 34.1% in the anterior chamber of the eye. Corresponding figures for the savanna villages were 51.9%, 20.5%, 5.6% and 21.8%. The overall prevalence of nodules in the forest and savanna was 70.5% and 53.2% respectively, while the prevalence of head and upper body nodules was 14.8% (forest) and 11.0% (savanna). The prevalence of moderate or severe skin lesions was 17.7% in forest and 13.0% in savanna villages. Lesions of the groin and scrotum were few in both zones. In persons aged 30 years or more the prevalence rates of severe eye lesions--sclerosing keratitis, iritis, optic atrophy and choroidoretinitis--were 4.3%, 16.1%, 13.9% and 14.8% respectively in forest villages. Corresponding figures for the savanna villages were 3.7%, 8.7%, 14.2% and 11.3%. Males were more commonly affected than females. At least one of these lesions was found in 32% persons in forest and 24% in savanna villages.

Onchocerciasis in Gilgel Ghibe River valley Southwest Ethiopia

“…Male preponderance is consistent with other observations in Ethiopia (1,(5)(6)(7) and elsewhere (19,20).…”

Impact of five annual rounds of mass drug administration with ivermectin on onchocerciasis in Sierra Leone

“…It has been suggested that the regional and district variations of onchocerciasis prevalence at baseline could be linked with vector ecology and density, which also depend on the distance of villages studied from the river basin and the geography of the river [ 39 ]. Previous studies in Sierra Leone showed that O. volvulus MF prevalence was higher in the forest (71.8%) than in Savannah villages (51.9%) [ 30 ]. In general, the eastern region has the forest strain of the O. volvulus parasite, characterised by low intensity of infection, mild skin disease and relatively low blindness rate; the southern region has a mixture of forest and Savannah strains of the parasite, characterised by high infection intensity, mild skin disease and relatively higher blindness rate (sometimes higher than blindness rates recorded in the Savannah area); and the northern region has the Savannah strain of the parasite, characterised by high infection intensity, mild skin disease, and relatively high blindness rate [ 14 , 34 ].…”

The unusual occurrence of savanna members of the Simulium damnosum species complex (Diptera: Simuliidae) in southern Sierra Leone in 1988

“…These studies show that the disease is virtually ubiquitous in adults in many of the rural areas and that onchocercal blindness is present, though rarely at a prevalence higher than 2.5%. However, a few foci of severe onchocerciasis, comparable with those of hyperendemic villages in savanna West Africa, have been shown to occur in some forest areas (McMahon et al, 1988).…”