Abstract
Background
Malaria remains a public health issue in Zambia and insecticide-based vector control is the main malaria elimination strategy. Success of vector control is dependent on a clear understanding of bionomics and susceptibility of the local vectors to insecticides used. Therefore, this study was conducted to generate baseline data on vector behaviour and phenotypic resistance for effective vector control programming.
Methods
Data collection was conducted in Ndola district from July 2021 to October 2021 from four sites; two peri-urban and two rural sites using Centre for Disease Control – light traps (CDC – LT), Pyrethrum Spray Catches (PSC) and Larval Collection. Mosquito identification was done using standard identification keys and Polymerase Chain Reaction (PCR). Williams’s mean was used to determine mosquito densities and Kruskall Wallis H test was used to compare the distribution of mosquitoes. A negative binomial with a log link function was used to determine factors affecting mosquito counts. Susceptibility of the local vectors was determined using WHO tube and CDC bottle bioassay.
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 and Anopheles gambiae were found to coexist in all the four sites with An. funestus identified as the most dominant malaria vector. Densities of An. gambiae s.s were found to be higher in urban than rural sites compared to An. funestus s.s which had similar distribution across the four study sites. Sprayed houses were significantly associated with reduced mosquito numbers (B = -0.956, IRR = 0.384, P ˂ 0.05). An. gambiae s.s 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. Agriculture practices in peri-urban areas resulted in highly productive mosquito breeding sites, thus the need for targeted vector control. Lastly, the two main vectors in Ndola vary in bionomics and control measures must be tailored to these findings.