Independent evaluation of onchocerciasis rapid assessment methods in Benue State, Nigeria.

OBJECTIVE

To evaluate the prevalence of palpable nodules or skin depigmentation as rapid indicators of onchocerciasis epidemicity in at-risk communities.

METHOD: We examined data collected in Benue State on 11035 individuals in 32 villages to evaluate these rapid assessment methods.

RESULTS

The prevalence of palpable nodules correlates more closely with microfilarial prevalence (r=0.68, P<0.001) and community microfilarial load (r=0.64, P<0.001) than the prevalences of skin depigmentation or other potential rapid indicators. The recommended cut-off value for palpable nodules of 20% or more in males aged >20 years had a sensitivity of 94% and specificity of 50% compared to a cut-off of 40% or more for microfilarial prevalence in all ages. This would mean that in these 32 villages 17 of 18 would have been correctly identified for treatment, and a further 7 at lesser risk would have been targeted for treatment.

CONCLUSIONS

Skin snipping and parasitological examination can be replaced by the simpler method of palpating onchocercal nodules to identify communities at serious risk of onchocerciasis. This has important operational benefits for onchocerciasis control programmes.