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

Abstract

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.

Parasitological and clinico-epidemiological features of onchocerciasis in West Wellega, Ethiopia

“…A large multi-country study has shown that OSD entails a grave burden and that its symptoms have significant personal and psycho-social effects, not only on the affected individuals but also on their families and communities (Murdoch et al 2002). Of the clinical spectra of onchocerciasis, pruritus was the most frequently observed symptom among the study subjects, which is often very serious and the main cause of sleeplessness, fatigue and weakness.…”

“…While the disastrous effects of ocular damage by river blindness have always been high priority as a public health problem, skin disease has received scant attention. Nonetheless, large multi-country studies have recently shown that onchocercal skin disease (OSD) entails a grave burden and that its symptoms have significant personal and psycho-social effects, not only on the affected individuals but also on their families and communities (Murdoch et al 2002). In Ethiopia, eye lesions and blindness due to the disease appear to be absent or uncommon (WHO 2010).…”

Itch in Ethnic Populations

“…Onchocerciasis is currently endemic in 30 African countries, Yemen, and isolated regions of South America. A study to assess the true public-health importance of onchocercal skin disease throughout the African region was conducted in 7 centers (3 in Nigeria and 1 each in Ghana, Cameroon, Tanzania and Uganda) and involved 5459 subjects (69). A strong correlation was found between the prevalence of itching, which affects 42% of the population aged 20 years, and the level of endemicity, which was measured by the prevalence of onchocercal skin lesions.…”

The geographic distribution of onchocerciasis in the 20 participating countries of the African Programme for Onchocerciasis Control: (1) priority areas for ivermectin treatment

“…In each selected village a sample of adults is examined for the presence of palpable subcutaneous onchocercal nodules and the prevalence of nodules is calculated. Previous studies had shown that the severity of onchocercal disease in the community, and thus its public health importance, is related to the level of onchocerciasis endemicity as also reflected in the prevalence of nodules [2,66,67]. Based on available data on this relationship, an expert committee recommended in the early 1990s that, in order to control onchocerciasis as a public health problem, ivermectin treatment should be provided to all high risk communities where the prevalence of onchocercal nodules in adults was greater than 20% [68].…”