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

Objectives To assess vector behaviour and phenotypic resistance for effective vector control programming. Design This was a cross-sectional study. Setting This study was conducted in the urban and periurban areas of Ndola district, Zambia. Participants/study units 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. Primary and secondary outcome measures The primary outcome was the behaviour of the malaria vectors, and the secondary outcome was their phenotypic resistance status. Results 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. Anopheles funestus sensu stricto (An. funestus s.s) and Anopheles gambiae sensu stricto (An. gambiae s.s) were found to coexist in all the four sites, with An. funestus s.s identified as the most dominant malaria vector. Densities of An. gambiae s.s, seeking a blood meal (χ 2 =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 An. funestus s.s, 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). Anopheles gambiae was fully susceptible to organophosphates and neonicotinoids but highly resistant to pyrethroids, carbamates and organochlorines. Conclusions The emergence of An. funestus s.s in an area previously dominated by An. gambiae s.s and its coexistence with An. gambiae s.s 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.