Onchocerciasis is not a major cause of blindness in two endemic villages in Sierra Leone.

Objective: Sierra Leone, a country where onchocerciasis is endemic in 14 of the 16 districts, was the focus of our investigation. Despite 17 rounds of annual ivermectin treatment since 2005, a report circulated by a local politician indicated an increase in cases of suspected onchocerciasis-related vision impairment in two villages (Mangobo and Petifu) in Tonkolili district. In response, the National Neglected Tropical Disease Program conducted a comprehensive investigation. Ophthalmological, parasitological, and serological tests were conducted using standard procedures to determine the relationship between self-reported vision loss and onchocerciasis in adults. In addition, serological tests were carried out on children aged 5 to 9 years to assess the recent status of exposure to onchocerciasis in the two villages.

Results: Reported vision loss in 37 patients was mainly due to cataracts (35.1%), allergic conjunctivitis (18.9%), refractive error (10.8%), and other conditions not related to onchocerciasis. There were 40.7% of all adults (N = 54) tested and 29.0% of 31 persons with self-reported vision loss who were positive for Ov-16 IgG4 antibodies, suggesting a history of exposure to onchocerciasis. However, otoscopic eye examinations and microscopic skin snip tests were all negative for Onchocerca volvulus microfilariae, indicating no active or low-intensity infection among adults and a low or zero risk of serious ocular morbidity in the two villages. Onchocerciasis may no longer be a major cause of blindness in these two villages. Apparently, 4.6% of 153 children aged 5 to 9 years tested positive for Ov-16 IgG4 antibodies, suggesting that onchocerciasis transmission is likely still ongoing in the two villages. The data presented here suggest that more annual rounds of mass treatment with ivermectin with high coverage are needed to eliminate onchocerciasis transmission in this area.