Population genetics of anopheles funestus and anopheles gambiae (diptera: culicidae) with reference to insecticide resistance on mainland Nchelenge and the neighbouring islands on lake Mweru in Zambia.
Date
2024
Authors
Muleba, Mbanga
Journal Title
Journal ISSN
Volume Title
Publisher
The University of Zambia
Abstract
Vector control strategies based on available entomological information have not impacted malaria transmission in Nchelenge. Prior studies carried out in the district determined the identity and bionomics of the main malaria vectors as well as their status of insecticide resistance. However, this information was confined to the mainland and inadequately covered malaria vector populations. An understanding of the population attributes of the major vectors in different areas of the district was needed. The overall goal of this study was to generate valuable information on malaria vector population genetics and insecticide resistance for the National Malaria Elimination Programme. The study included two major malaria vector mosquito species in the district, namely, Anopheles (Cellia) funestus s.s. Giles, 1900, and Anopheles (Cellia) gambiae s.s. Giles, 1902. The insecticide classes tested included carbamates, organochlorines, organophosphates, and pyrethroids. A total of 6068 Anopheles mosquitoes were collected indoors from four sites, including islands on Lake Mweru in Nchelenge district, between 2014 and 2016. A representative subsample of the collection was
processed for molecular and ELISA laboratory analyses, and 394 specimens of this subsample had a fragment of their ITS2 DNA sequenced. Vector infectivity was assessed, and insecticide resistance tests were conducted on both wild and F1 mosquitoes. Based on the ITS2 sequences in both vectors, there was diversity within populations with no fixed genetic differences across the collection sites. Anopheles gambiae was more abundant on Kilwa island (71%; n = 178), and An. funestus was on Chisenga island (78%; n = 4275). Anopheles funestus was more abundant during the dry season (76%) and predominated in every collection except one from Kilwa Island. Anopheles gambiae was abundant during the rainy season (65%). Malaria infectivity in Anopheles funestus spanned all sites and seasons. Kilwa Island and Mainland both had 3.7% of An. funestus tested (n = 164) and (n = 82), respectively, infected with P. falciparum sporozoites in the dry season, and 7.1% and 5.9% of An. gambiae tested (n = 84) and (n = 17),
respectively, in the rainy season. Chisenga Island had 3.2% of the tested An. funestus (n = 188) infected with P. falciparum. Insecticide resistance, i.e., mortality less than 98%, was recorded against pyrethroids (mortality, 35–84%) and carbamates (mortality, 38– 96%). No resistance was recorded against organophosphates (mortality, 100%). Anopheles funestus was susceptible to organochlorines (mortality, 100%), in contrast with An. gambiae (mortality, 10%). Resistance intensity to deltamethrin (time to 50% mortality, 2–5 hours) and bendiocarb (time to 50% mortality, 2–7 hours) was very high in An. funestus. All 88 An. gambiae that were tested had the knockdown resistance (kdr west) allele (L1014F), and 14% of them also had the east kdr (L1014S). Insecticide resistance on islands against carbamates could be due to cross-resistance conferred through the widely used pyrethroid-treated bed nets. Vector control should be scaled up and embrace new-generation LLINs with piperonyl butoxide to manage resistance in island vector populations.
Description
Thesis of Doctor of Philosophy in Biological Sciences (Entomology).