n African Entomology - Impact of the Okyereko irrigation project in Ghana on the risk of human malaria infection by species (Diptera : Culicidae)




The impact of an irrigation scheme on malaria transmission in coastal savanna was studied. Adult mosquitoes (Diptera : Culicidae) were sampled using human landing and pyrethrum spray catches at Okyereko (irrigated village) and at Bewadze (non-irrigated, 9.5 km away) during the dry season of 2002/2003. Each mosquito was first identified morphologically as Giles, then to sibling species by PCR and forms were further identified by restriction analysis. The parity of mosquitoes were determined and ELISA-based methods used to determine sporozoite infections and host blood meal source. More mosquitoes were obtained at Okyereko. Members of the complex were dominant at Okyereko and at Bewadze. Within the complex, only was identified, and the M form constituted 91.7 % at Okyereko and 66.7 % at Bewadze. The biting rate was higher at Okyereko, but parous rates were similar in both villages. The infection rates were 2.5-fold higher in than at both sites, but were 17.5-fold lower at Okyereko. At Okyereko, the four infective were found to be the M form while at Bewadze three of the four infective were found to be the S form and one was the M form. The entomological inoculation rate was also significantly lower at Okyereko. The human blood index was 84.1 % at Okyereko and 77.1 % and Bewadze. Malaria risk was therefore lower at the irrigated village and the likely reason is the low numbers of and S form.


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