Onchocerciasis: the clinical and epidemiological burden of skin disease in Africa.

An attempt was made to assess the true public-health importance of onchocercal skin disease throughout the African region and hence provide an objective basis for the rational planning of onchocerciasis control in the area. The seven collaborative centres that participated in the study (three in Nigeria and one each in Ghana, Cameroon, Tanzania and Uganda) were all in areas of rainforest or savannah-forest mosaic where onchocercal blindness is not common. A cross-sectional dermatological survey was undertaken at each site following a standard protocol. At each site, the aim was to examine at least 750 individuals aged 5 years and living in highly endemic communities and 220-250 individuals aged 5 years and living in a hypo-endemic (control) community. Overall, there were 5459 and 1451 subjects from hyper-and hypo-endemic communities, respectively. In the highly endemic communities, the prevalence of itching increased with age until 20 years and then plateaued, affecting 42% of the population aged 20 years. There was a strong correlation between the prevalence of itching and the level of endemicity (as measured by the prevalence of nodules; r=0.75; P<0.001). The results of a multivariate logistic regression analysis showed that, at the individual level, the presence of onchocercal reactive skin lesions (acute papular onchodermatitis, chronic papular onchodermatitis and/or lichenified onchodermatitis) was the most important risk factor for pruritus, with an odds ratio (OR) of 18.3 and 95% confidence interval (CI) of 15.19-22.04, followed by the presence of palpable onchocercal nodules (OR=4.63; CI=4.05-5.29). In contrast, non-onchocercal skin disease contributed very little to pruritus in the study communities (OR=1.29; CI=1.1-1.51). Onchocercal skin lesions affected 28% of the population in the endemic villages. The commonest type was chronic papular onchodermatitis (13%), followed by depigmentation (10%) and acute papular onchodermatitis (7%). The highest correlation with endemicity was seen for the prevalence of any onchocercal skin lesion and/or pruritus combined (r=0.8; P<0.001). Cutaneous onchocerciasis was found to be a common problem in many endemic areas in Africa which do not have high levels of onchocercal blindness. These findings, together with recent observations that onchocercal skin disease can have major, adverse, psycho-social and socio-economic effects, justify the inclusion of regions with onchocercal skin disease in control programmes based on ivermectin distribution. On the basis of these findings, the World Health Organization launched a control programme for onchocerciasis, the African Programme for Onchocerciasis Control (APOC), that covers 17 endemic countries in Africa.

Three probable cases of Loa loa encephalopathy following ivermectin treatment for onchocerciasis.

Over the past nine years, more than 12 million people exposed to Onchocerca volvulus infection have received at least one dose of ivermectin, almost all without serious adverse reactions. Since 1991, however, several cases with neurologic manifestations, including coma, have been reported after ivermectin treatment of persons infected with O. volvulus who also had concomitant Loa loa infection with very high microfilaremia (> 50,000 microfilariae/ml of blood). In 1995, four criteria were established to define probable cases of Loa encephalopathy temporally related to treatment with ivermectin (PLERI). The present paper describes three PLERI cases recorded in Cameroon and compares them with two others reported previously. Disorders of consciousness began 3-4 days after treatment. The objective neurologic signs were variable. The conditions improved favorably in three patients who benefited from early hospitalization and good nursing; their disorders of consciousness lasted only 2-3 days; the results of clinical examination became normal after one month and electroencephalographic abnormalities disappeared after 5-7 months. Conversely, late diagnosis and delay in proper management in two others probably led to worsening of the condition and to fatal outcome related to the usual complications of coma. In addition to these cases, patients w with high Loa microfilaremia also developed milder neurologic manifestations causing functional impairment lasting for at least one week after treatment. Before launching mass ivermectin distribution programs to control onchocerciasis in central Africa, communities in which the intensity of concomitant L. loa microfilaremia is high need to be identified, and specific educational measures and monitoring strategies should be developed and applied before they are treated.

Country-wide rapid epidemiological mapping of onchocerciasis (REMO) in Cameroon.

The prevalence of infection in local communities has been used as the basis for the country-wide repartition of onchocerciasis in Cameroon, following the principles for rapid epidemiological mapping of onchocerciasis (REMO) developed by the World Health Organization. The levels of endemicity were evaluated in 349 villages by rapid epidemiological assessment (REA), a method based on the examination of nodules in males aged > or = 20 years. An onchocerciasis map was then drawn from the epidemiological data which had been collected previously, from clinico-parasitological surveys based on the examination of skin snips, and the results of the REA surveys. The REMO surveys allowed the main onchocerciasis foci in Cameroon to be accurately delineated, and several small endemic areas which had never been reported before to be identified. The total 'at risk' population (i.e. those for which ivermectin treatment should be considered as urgent or highly desirable) was estimated by combining the epidemiological results and the demographical data available from an administrative census. Those at risk were estimated to number 3.5 million, representing about 50% of the total rural population in Cameroon.

A rapid mapping technique for the prevalence and distribution of onchocerciasis: a Cameroon case study.

A rapid and cheap method for mapping the endemicity levels of onchocerciasis in both forest and savanna areas, where the vectors are members of the Simulium damnosum complex, is described. The selection of the study communities is based on a general understanding of the vectors' ecology and biassed towards those at highest risk of onchocerciasis, although there must be adequate geographical coverage. In a case study in Cameroon, prevalences were determined, using the non-invasive nodule palpation technique, in samples, each of 30-50 adult males, from 49 villages in six study areas in Cameroon. The method proved effective in the rapid mapping of onchocerciasis distribution in all areas studied, in which the distribution patterns varied from the classical linear to diffuse, and in one area with an anomalous distribution. The method should prove of value in the design of national onchocerciasis control programmes.