Clinical and parasitological aspects of itching caused by onchocerciasis in Morogoro, Tanzania.

A clinical and parasitological assessment of onchodermatitis was conducted in a rural area of Morogoro district, Tanzania. The study population consisted of 1,005 individuals aged > or = 5 years: 749 from a hyper-endemic community and 256 from a hypo-endemic. The prevalence of troublesome itching was 67.0% in the hyper-endemic community but only 5% (13/256) in the hypo-endemic. The corresponding prevalences of nodules among the adult male subjects were 77.7% (171/220) and 2.3% (2/86). The most common onchocercal skin lesion in the hyper-endemic community was chronic papular onchodermatitis (CPOD) manifested by itching, which was often very severe. There was a strong association between skin itching and endemicity (r = 0.75; P < 0.001). The prevalence of CPOD in the hyper-endemic community was significantly higher in males than females (P< 0.001). CPOD was only observed in subjects aged > or = 7 years. Many of the subjects were checked for microfilaridermia, by skin-snipping. The prevalence of microfilaridermia [58.2% (393/675) v. 6.2% (3/48)] and its geometric mean intensity (8.9 v. 1.0 microfilariae/mg skin snip) were both higher in the hyper-endemic community than the hypo-endemic. Itching appears to be related to reactive onchodermatitis.