Abstract
BackgroundThe movement of malaria vectors into new areas is a growing concern in the efforts to control malaria. The recent report of Anopheles stephensi in eastern Ethiopia has raised the necessity to understand the insecticide resistance status of the vector in the region to better inform vector-based interventions. The aim of this study was to evaluate insecticide resistance in An. stephensi in eastern Ethiopia using two approaches: (1) World Health Organization (WHO) bioassay tests in An. stephensi; and (2) genetic analysis of insecticide resistance genes in An. stephensi in eastern Ethiopia.MethodsMosquito larvae and pupae were collected from Kebri Dehar. Insecticide susceptibility of An. stephensi was tested with malathion 5%, bendiocarb 0.1%, propoxur 0.1%, deltamethrin 0.05%, permethrin 0.75%, pirimiphos-methyl 0.25% and DDT 4%, according to WHO standard protocols. In this study, the knockdown resistance locus (kdr) in the voltage gated sodium channel (vgsc) and ace1R locus in the acetylcholinesterase gene (ace-1) were analysed in An. stephensi.ResultsAll An. stephensi samples were resistant to carbamates, with mortality rates of 23% and 21% for bendiocarb and propoxur, respectively. Adult An. stephensi was also resistant to pyrethroid insecticides with mortality rates 67% for deltamethrin and 53% for permethrin. Resistance to DDT and malathion was detected in An. stephensi with mortality rates of 32% as well as An. stephensi was resistance to pirimiphos-methyl with mortality rates 14%. Analysis of the insecticide resistance loci revealed the absence of kdr L1014F and L1014S mutations and the ace1R G119S mutation.ConclusionOverall, these findings support that An. stephensi is resistant to several classes of insecticides, most notably pyrethroids. However, the absence of the kdr L1014 gene may suggest non-target site resistance mechanisms. Continuous insecticide resistance monitoring should be carried out in the region to confirm the documented resistance and exploring mechanisms conferring resistance in An. stephensi in Ethiopia.
Highlights
The movement of malaria vectors into new areas is a growing concern in the efforts to control malaria
Anopheles stephensi insecticide resistance A total of 1200 An. stephensi larvae and pupae were collected from the breeding sites
Bioassay results A total of 700 An. stephensi were tested with different insecticides based on World Health Organization (WHO) protocol
Summary
The movement of malaria vectors into new areas is a growing concern in the efforts to control malaria. The recent report of Anopheles stephensi in eastern Ethiopia has raised the necessity to understand the insecticide resistance status of the vector in the region to better inform vector-based interventions. Malaria remains a major health problem in 2017, an estimated 219 million cases of malaria occurred worldwide, with 435,000 deaths [1]. In Ethiopia, malaria remains a major public health concern with millions of cases and thousands of deaths reported annually [2]. Yared et al Malar J (2020) 19:180 confirmed This mosquito was first detected in the Somali Regional State of Ethiopia in 2016 [4] and has subsequently been confirmed to have a broad distribution in Northeast and east Ethiopia [5]. In Somali region carbamate insecticides have been frequently sprayed during active malaria season in collaboration by Federal Ministry of Health (FMOH) with the regional Health Bureau
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