Onchocerciasis: Relationships Between infection Load, Skin Manifestations and Socio-Econolvilc Indices in Pawl Area, North Western Ethiopia

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Addis Ababa University


A study to detennine a rapid screening method for onchoceciasis was conducted between April 10 and July 15 1996 in a populations of 5 villages, Manbuk area located in Pawi, North west Ethiopia. Out of the total 3,385 censused persons 766 (22.6%) residents of age five years and above, of whom 509 (66.4%) were heads of household, were included in the study. The 509 heads of household were interviewed to explore information on the socio-economic indices and about the populations knowledge of onchoceciasis. Parasitological and skin examination were conducted on the 766 individuals who showed up to participate in the study. Results of the questionnaire survey indicated that the community actually knows about onchocerciasis, including its social and economic impacts. The parasitological examination by using skin snips revealed an overall prevalence of 43.7 % and a geometric mean microfilarial density (MFD) of 13.62 mf/mg both reaching peak at the age of 25-34 years, especially among males. Farmers and those in the lower socio-economic strata appeared to' be at more risk of infection. A relatively higher prevalence and MFD was found in the indigenous population than settlers. Skin examination revealed the presence of acute papular onchodermatitis (APOD), chronic papular oochWermatitis (CPOD), depigmentation (DPM) and palpable onchocercal nodules (PON) in a higher proportion of the population. The major skin manifestations were highly correlated with infection load, with correlation coefficients (r) of 0.81,0.83,0.82,0.79, and 0.89 for APOD, CPOD, LOD, DPM AND PON, respectively. This indicated that anyone of the major skin manifestations may be used to identify high risk communities for correlation with both skin snip prevalence and microfilarial load. Furthermore, even lay men can be trained to quickly diagnose it because of its most obvious clinical presentation. Strong relationships also were detected between skin manifestations and socio-economic variables, with farmers and poorer persons in other occupation tending to have more severe skin manifestation. In conclusion, it is recommendable that: a) members of the lower economic strata in general, and the indigenous population and farmers in particular be given high priority in onchocerciasis control programs; b) the PON detection technique, in comparable ecogeographic regions of Ethiopia, for rapid screening of communities and mapping of onchocerciasis, be adopted; c) selection of 30% nodules which corresponds to a 90% skin snip prevalence in adult population can be used as the most appropriate local criteria for assigning a community as a high priority for control. '