Seventeen years of annual distribution of ivermectin has not interrupted onchocerciasis transmission in North Region, Cameroon.

We studied onchocerciasis transmission and impact on ocular morbidity in three health districts in North Region, Cameroon, where annual mass ivermectin treatment has been provided for 12-17 years. The studies, which took place from 2008 to 2010, consisted of skin snips for microfilariae (mf), palpation examinations for nodules, slit lamp examinations for mf in the eye, and Simulium vector dissections for larval infection rates. Adults had mf and nodule rates of 4.8% and 13.5%, respectively, and 5.5% had mf in the anterior chamber of the eye. Strong evidence of ongoing transmission was found in one health district, where despite 17 years of annual treatments, the annual transmission potential was 543 L3/person per year; additionally, children under 10 years of age had a 2.6% mf prevalence. Halting ivermectin treatments in North Cameroon now might risk recrudescence of transmission and ocular disease.

Does onchocerciasis transmission take place in hypoendemic areas? a study from the North Region of Cameroon.

OBJECTIVE: Community-directed treatment with ivermectin (CDTI) for onchocerciasis control is targeted to meso and hyperendemic areas in Africa. Below the threshold, communities are considered hypoendemic and, mass treatment is not recommended. As policy begins to shift from control to elimination, the role of hypoendemic areas in maintaining Onchocerca volvulus needs to be re-examined. The study determined whether independent transmission occurs in a hypoendemic area in the North region of Cameroon. METHODS: Ten 'high risk' communities along the River Mayo Douka system in Ngong Health District, at least 20 km from the nearest CDTI program were studied. Six hundred and forty-nine adults (over 20 years of age) and 561 children (under 10 years) were examined for nodules and microfilaria. A subsample of 334 adults was examined for onchocercal ocular morbidity. Simulium flies from 4 collection points were captured over 3 months annually for 2 years and dissected for larval stages of O. volvulus. RESULTS: Nodule and microfilariae (mf) prevalence among adults was 12.20% and 2.91%, and 9.2% and 0.48% among children, respectively. Blindness because of onchocerciasis was insignificant, although low rates of chronic onchocercal ocular disease (<2%) were observed. Four (0.16 percent) of 255 flies collected in 2008 were infected with L3 larval stage, and 1 black fly of 39 collected in 2009 had two L2 larval stage morphologically consistent with O. volvulus. CONCLUSION: Ngong is a 'hypoendemic' focus with likely low grade indigenous transmission in isolation from meso/hyperendemic areas. Consequently, transmission from hypoendemic areas could contribute to rapid disease recrudescence in the post-treatment phase of adjacent former meso and hyperendemic areas.