East African Medical Journal

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

TL Lakwo


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.

East African Medical Journal Vol. 81 No. 5 May 2004: 244-247
AJOL African Journals Online