Onchocerciasis And The Pattern Of Ocular Manifestations In Southwest, Nigeria

Objective: Onchocerciasis remains endemic in parts of Nigeria despite prolonged ivermectin distribution, with residual transmission and associated ocular morbidity insufficiently characterized. This study assessed the prevalence of onchocerciasis using combined clinical, microscopic, and molecular approaches and described the pattern of ocular manifestations in Osun State, Nigeria. Methodology: A community-based quasi-experimental study was conducted among consented 600 adults aged 20 years and above, selected through multistage probability sampling. Data collection included structured questionnaires, ocular examinations, nodular palpation, skin-snip microscopy, and polymerase chain reaction (PCR) detection of Onchocerca volvulus DNA. Visual acuity (VA) was measured using distance Snellen VA chart, anterior segment was assessed with pen torches and binocular loop magnifier while posterior segment was assessed with direct ophthalmoscope and associations between infection and environmental factors were analyzed. Results: Nodular prevalence was 17.2%, ocular morbidity 15.2%, microscopy positivity 2.3%, and PCR positivity 31.0%. Corneal lesions accounted for 52.7% of ocular manifestations. Molecular positivity peaked among individuals aged 40–49 years, while nodular and ocular disease were highest in the 50–59-year group. Living within five kilometres of a river was significantly associated with infection. Microscopy showed low sensitivity (40%), whereas PCR demonstrated high sensitivity (97%). Conclusion: The substantial burden of corneal disease highlights the need for routine ocular screening and early intervention. High molecular prevalence indicates ongoing low-density transmission undetected by conventional microscopy, underscoring the need to integrate molecular diagnostics into elimination programmes.