Onchocerciasis in Anambra State, Southeast Nigeria: endemicity and clinical manifestations.

BACKGROUND

A cross-sectional study was performed to determine the current endemicity of onchocerciasis in Ayamelum Local Council, Anambra State, Southeast Nigeria, where community-directed treatment with ivermectin has been implemented for over a decade.

METHODS

An estimate of the endemicity of onchocerciasis was obtained using the rapid assessment method in 894 subjects from 13 communities selected by multistage sampling. Dermatological and ocular manifestations were analysed and classified using standard criteria.

RESULTS

Onchocerca volvulus nodules were recorded in 86 (9.6 ± 1.9%) of the subjects, and 186 (20.8 ± 3.7%) had one or more of the various classes of onchocercal skin diseases (OSD). Prevalence was dependent on age (p = 0.001), but not on sex (p = 0.31). There was a total absence of symptoms in the youngest age group and a low prevalence among subjects in their second decade of life. Pearson's correlation showed a strong positive correlation between nodular rate and prevalence of chronic papular onchodermatitis (r = 0.943) and a poor correlation with acute papular onchodermatitis (r = 0.259). Age-dependent analysis of various classes of OSDs showed that the rate of acute papular onchodermatitis increased with age up to the third decade of life and decreased steadily thereafter, while the chronic forms of OSD increased with age for both sexes. Infection was dependent on occupation and proximity of the village to the vector breeding sites.

CONCLUSIONS

Generally low prevalence in the population and absence of symptoms among the youngest age group emphasise the success of the intervention, but the persistent occurrence of acute disease may suggest a shortfall due to low coverage or non-compliance with the mass chemotherapeutic regimen.