An evaluation of the effectiveness of integrated control onchocerca volvulus transmission by simulium naevei in Kashoya-Kitomi focus in Uganda.

Abstract

This study was carried out to evaluate the extent to which 18 years of mass treatment with ivermectin and one year of integrating both vector elimination and mass treatment had suppressed Onchocerca volvulus transmission in the hyperendemic Kashoya- Kitomi focus. The objectives were to determine the impact of the integrated control on O. volvulus transmission and the monthly biting rate of Simulium naevei. The flies were collected from 4 sites of Kabuhweju, Kategule, Kiyanja and Kaziko from May 2007 to July 2008 and screened for O. volvulus using the O-150 PCR technique. The prevalence of infective flies in the 264 pools of 20 heads was 0.0011% in 2007 compared to 8.0% in 1991 (P<0.001). After 18 years of mass treatment alone, transmission of onchocerciasis still continued. One year of ground larviciding rivers with temephos interrupted the transmission by elimination of vectors. The monthly biting density of S.naevei was significantly reduced from 835.8 bites/man/month in May 2007 to 0 in June 2008 (P<0.001). The findings show that the integrated strategy using Community Directed Treatment with Ivermectin and ground larviciding is effective in suppressing O. volvulus transmission. Furthermore vector elimination is important if onchocerciasis is to be eliminated from a hyperendemic focus as CTDI alone reduces the prevalence of infective larvae in the vector, but does not completely eliminate them. Continuous biannual treatment of communities with ivermectin and monitoring the vector population are necessary until surveys show complete elimination of skin microfilariae and adult worms from the human population.