Insecticide Resistance in Anopheles stephensi in Somali Region, Eastern Ethiopia

Abstract

Background: 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. 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. Methods: Mosquito larvae and pupae were collected from Kebridehar. 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. Results: All An. stephensi samples were resistant to carbamates, with mortality rates 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 voltage gate sodium channel gene (vgsc) revealed the absence of kdr L1014 mutations. Conclusion: Overall, 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.

Evolution of insecticide resistance and its mechanisms in Anopheles stephensi in the WHO Eastern Mediterranean Region

“…Anopheles stephensi has recently invaded new territories and countries in Asia and the Horn of Africa [49][50][51][52][53][54]. In this invasion, the mosquito takes its insecticide resistance heritage with it as in studies on the insecticide resistance in An.…”

“…In this invasion, the mosquito takes its insecticide resistance heritage with it as in studies on the insecticide resistance in An. stephensi in Ethiopia and Sri Lanka, the species was resistant to major groups of insecticides [54,55]. Therefore it might be worthwhile to identify the origin of the mosquito should it appear in a new territory.…”

“…stephensi was resistant to insecticides of all major classes. Mortality after exposure to the discriminating concentrations of DDT, malathion, pirimiphos-methyl, bendiocarb, propoxur, permethrin and deltamethrin were 32%, 32%, 14%, 23%, 21%, 53% and 67%, respectively, revealing relatively high resistance to all those insecticides [54]. The susceptibility status of An.…”

“…The site insensitivity resistance mechanisms in An. stephensi from Ethiopia was studied but no kdr or ace1 traits were detected, this may imply the involvement of metabolic mechanisms [54].…”

“…stephensi expanded its distribution range into Sri Lanka and the Horn of Africa, where it has been detected in Djibouti, Ethiopia and Sudan [49][50][51][52][53][54]. The species in Ethiopia was highly resistant to DDT, malathion, pirimiphos-methyl, bendiocarb, propoxur, deltamethrin, and permethrin [54]. Resistance to insecticides was also detected in An.…”