Preliminary studies on the biting activity and transmission of Onchocerca volvulus by Simulium neavei (diptera: simuliidae) in Kashoya-Kitomi focus, Western Uganda.

OBJECTIVE To determine the biting activity and onchocerciasis transmission in Kashoya-Kitomi focus, Western Uganda. DESIGN Cross-sectional survey in randomly selected sites. SETTING Three districts in Western Uganda. METHOD Crab trapping and examination for immature stages of Simulium neavei and full day human bait catches and dissections were conducted at three sites. RESULTS A total of 338 crabs were caught and out of this 372 (95.9%) were positive with immature stages of S. neavei with mean S. neavei/crab of 6.9. High biting density of S. neavei was observed in the two sites in Kabarole and Mbarara districts whereas an extremely low density was observed at a site in Bushenyi. Diurnal biting pattern revealed two peaks in the morning (09:00-10:00 hours.) and in the late afternoon (14:00-15:00 hours.) with a mid-day lull. The infection/infective rates were 53.3/11.0%, 30.7% to 7.8% and 20.0/0% for sites in Mbarara, Kabarole and Bushenyi districts, respectively. Monthly biting rates/ Transmission potentials for Mbarara, Kabarole and Bushenyi districts were 6231/5437, 9244/2916 and 247/0. CONCLUSION There was high transmission of onchocerciasis observed in Kashoya-Kitomi focus despite the ongoing ivermectin treatment. The need for improved chemotherapeutic coverage and instituting other control measures may be necessary.