Transmission of onchocerciasis by Simulium Sanctipauli ‘Pra’ form in the Upper Denkyira District, Ghana after Mass Ivermectin Treatment

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The WHO has begun several control programmes to eliminate onchocerciasis. One of the programmes is the African Programme for Onchocerciasis Control (APOC). The aim of this project was to measure the impact of the mass treatment scheme in the Upper Denkyira District of Central Ghana. Three vector sampling sessions (1909, 2132 and 1165 flies respectively) using human-biting method were conducted. Molecular biological analysis was also undertaken to identify the species of filarial larvae found in the vectors. Questionnaires were administered to determine the proportion of the population that was covered by the treatment. Larvae were reared to adult and their morphological characters compared with wild caught blackflies. There was no significant reduction in the infection rates of the blackflies before and after the mass treatment. Infection rates per parous female blackflies were found to be consistently above 40% during all three sampling sessions. All larvae found in the vectors were Onchocerca volvulus. The vector was found to be an excellent host for Onchocerca volvulus with very low parasite mortality as they metamorphose from L1/L2 to the infective L3 stage. Vector infectiousness was two times higher in areas within 5km radius of the rivers than in areas more than 5km away (0.18 and 0.09 respectively). Less than 30% of the population participated in the treatment. Respondents who refused the drug administration gave the following reasons: travelled (3.9%), not important (5.8%), Not aware (10.6) unpleasant side effect (76.6%) and others (3.0%). The mass treatment was not effective due to the aversion of majority of the population to ivermectin. Management of adverse reaction after ivermectin therapy is recommended. The ‘Pra” form of Simuilium sanctipauli is highly antropophlic and efficient vector and this argues more for a semi-annual rather than an annual distribution of ivermectin.
A thesis Submitted to the Department of Clinical Microbiology, School of Medical Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, for the award of the degree of M.Phil. in Clinical Microbiology, 2003