Onchocerciasis: the burden of disease

The greatest burdens related to human onchocerciasis are the result of the eye and skin lesions and severe itching produced by the microfilariae. Although the major manifestations of the disease do show geographical variation (e.g. onchocercal blindness is not a common complication in all endemic countries), they are often sufficiently severe to prevent human use of the often very fertile land close to the rivers in which the vectors breed. Though for many years thought to be of relatively minor importance compared with onchocercal eye disease, the skin lesions of onchocerciasis have recently been shown to be a major socio-economic burden, in terms of disability-adjusted life-years. The demonstration of an excellent correlation between the prevalence of palpable nodules in a community and the community microfilarial load has led to the development of rapid, safe and non-invasive methods to assess and map the levels of endemicity across whole countries. This has enabled mass treatment with Mectizan (ivermectin, MSD) to be targeted first at hyperendemic communities. Estimates of the burden of onchocerciasis will continue to change as better means of measurement become available. It seems possible, however, that use of Mectizan will eliminate the disease before its true burden can be estimated accurately.