Onchocerciasis in the Upper Imo River Basin, Nigeria: Prevalence and Comparative Study of Waist and Shoulder Snips from Mesoen­demic Communities

Background: Onchocerciasis is endemic in the Imo River Basin, Nigeria. This study was aimed at assess­ing the prevalence and intensity of microfilaria of Onchocerca volvulus in the area. Methods: A cross-sectional study was carried out in the Okigwe Local Government Area, Imo State, Nige­ria. Two skin snips (one from the waist and another from the shoulder) were taken from 1024 individu­als examined. The survey coverage was high (91.8% of the study population). An individual was considered mf positive if either of the waist or shoulder snips or both were mf positive. The SPSS for Win­dows package was used for entering and analysis of data.Results: Thirty-seven percentage of those examined was positive for Onchocerca volvulus microfilariae (39.2% of males and 34.9% of females). The mf prevalence increased steadily with increasing age to reach 70.4% in the oldest age group. The overall mf Geometric Mean Intensity among mf positive individuals was 16 mf/skin snip and was significantly higher among males (18 mf/skin snip) than females (14 mf/skin snip) (p < 0.01). A scatter plot of microfilariae numbers in snips from the waist against numbers in snips from the shoulder of the same individuals, showed close correlation (Pearson's correlation coefficient = +0.90; p < 0.01), and those with mf intensities below 10 mf/snip had a more scattering tendency away from the regression line than those with higher mf intensities.Conclusion: Onchocerciasis is a public health concern in the area. Perhaps, 10 mf/snip is critical intensity threshold for reliable sampling using corneo-scleral punch