Implications for malaria transmission: a cross-sectional study on the bionomics and susceptibility of local malaria vectors in urban and periurban settings of Ndola district.

Abstract

To assess vector behaviour and phenotypic resistance for effective vector control programming. This was a cross-sectional study. This study was conducted in the urban and periurban areas of Ndola district, Zambia. A total of 166 houses were selected for adult mosquito collection, and an additional 60 collection efforts were made for larval collection from potential larval habitats. The primary outcome was the behaviour of the malaria vectors, and the secondary outcome was their phenotypic resistance status. The main breeding sites identified were irrigation trenches (4.67 larvae/dip) and garden ponds (2.72 larvae/dip) created from extensive urban agriculture practices. <i>Anopheles funestus sensu stricto (An. funestus s.s)</i> and <i>Anopheles gambiae sensu stricto (An. gambiae s.s)</i> were found to coexist in all the four sites, with <i>An. funestus s.s</i> identified as the most dominant malaria vector. Densities of <i>An. gambiae s.s,</i> seeking a blood meal (χ²=12.566, df=3, p=0.001) and resting indoors (Z=56.5, p=0.019), were found to be higher in urban than periurban sites compared with <i>An. funestus s.s</i>, which had similar distribution across the study sites. Sprayed houses were significantly associated with reduced mosquito numbers (B=-0.956, incidence rate ratio=0.384, p=0.001). <i>Anopheles gambiae</i> was fully susceptible to organophosphates and neonicotinoids but highly resistant to pyrethroids, carbamates and organochlorines. The emergence of <i>An. funestus s.s</i> in an area previously dominated by <i>An. gambiae s.s</i> and its coexistence with <i>An. gambiae s.s</i> in the dry season pose a risk of sustaining malaria transmission all year round. Agricultural practices in urban areas resulted in highly productive mosquito breeding sites; thus, there is a need for targeted vector control.