Abstract
Increased levels of insecticide resistance in major malaria vectors such as Anopheles funestus threaten the effectiveness of insecticide-based control programmes. Understanding the landscape features impacting the spread of resistance makers is necessary to design suitable resistance management strategies. Here, we examined the influence of the highest mountain in West Africa (Mount Cameroon; 4095 m elevation) on the spread of metabolic and target-site resistance alleles in An. funestus populations. Vector composition varied across the four localities surveyed along the altitudinal cline with major vectors exhibiting high parity rate (80.5%). Plasmodium infection rates ranged from 0.79% (An. melas) to 4.67% (An. funestus). High frequencies of GSTe2R (67–81%) and RdlR (49–90%) resistance alleles were observed in An. funestus throughout the study area, with GSTe2R frequency increasing with altitude, whereas the opposite is observed for RdlR. Patterns of genetic diversity and population structure analyses revealed high levels of polymorphisms with 12 and 16 haplotypes respectively for GSTe2 and Rdl. However, the reduced diversity patterns of resistance allele carriers revealed signatures of positive selection on the two genes across the study area irrespective of the altitude. Despite slight variations associated with the altitude, the spread of resistance alleles suggest that control strategies could be implemented against malaria vectors across mountainous landscapes.
Highlights
Vector control of mosquitoes is a critical part of the global strategy to manage mosquito-associated diseases, and insecticides are the most important component in this effort
Morphological identification of the 3194 females Anopheles revealed that they mostly belong to two major malaria vector species, An. gambiae complex (86%) and An. funestus group (12.2%) and three secondary vector species (1.6% An. hancocki, 0.2% An. nili s.l. and 0.03% An. ziemanni) (Figure S2), with a significant difference noted in the frequency distributions of Anopheles sp. between localities (p < 0.0001)
This study highlights for the first time the presence of glutathione s-transferases epsilon 2 (GSTe2)-based metabolic resistance and the GABA-receptor target-site mutation associated to dieldrin resistance in the malaria vectors
Summary
Vector control of mosquitoes is a critical part of the global strategy to manage mosquito-associated diseases, and insecticides are the most important component in this effort. Pyrethroids are the most widely used insecticides for indoor spraying against mosquitoes worldwide, owing to their efficacy and safety [2]. They are the main chemicals approved to treat mosquito nets [3,4], the main tool for human protection from malaria-carrying mosquitoes especially in Africa [1]. The widespread development of resistance in mosquitoes to the most commonly used insecticides negatively impacted the fight against mosquitoes in many areas [7] This has resulted in a number of outbreaks of mosquito-borne diseases in recent years [8,9]
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