Comparison of the use of skin scarification and skin biopsies to determine the prevalence and intensity of Onchocerca volvulus infection.

Two methods for the detection of Onchocerca volvulus microfilariae in the skin were compared in a population-based survey in Gatete, Murama and Jerama, three 'collines' (administrative units) in Burundi. Of the 513 subjects examined, each by both methods, 131 (25.5%) were found positive by skin scarification and 119 (23.2%) by membrane filtration of the fluid in which two skin snips had been incubated. Whilst the sensitivity of the two methods was similar (90% for scarifications and 82% for skin snips), more microfilariae were found by scarification than by biopsy (with geometric mean numbers of 9.1 and 4.1, respectively). Also, more of the cases with infections of low intensity (i.e. < or = 5 microfilariae detected) were found by scarification than by skin snipping (77.9% v. 60.3%; P = 0.06). The endemicity of onchocerciasis and age- and sex-specific prevalences and intensities of infection could be determined equally well using either method. The shortcomings of past comparisons between scarification and skin-snip methods are discussed. Skin scarification has many advantages for the detection of infected individuals in rural health centres and for use in population-based surveys. It may also be helpful when mixed filarial infections are present (especially where onchocerciasis and loiasis co-occur).