Mosquito Species Composition And Insecticide Resistance Status of Anopheles Arabiensis In Itang Special Woreda, Gambella, Southwestern Ethiopia

Abstract Introduction : Anopheles arabiensis , member species of the Anopheles gambiae complex, is the primary vector of malaria widely distributed in Ethiopia. Anopheles funestus, An. pharoensis and An. nili are secondary vectors occurring with limited distribution in the country. Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are pillars for the interventions against malaria control and elimination efforts in Ethiopia. However, the emergence and widespread of insecticide resistance in the major malaria vector, An. arabiensis , might compromise the efforts of the country. The aim of this study was to investigate composition of mosquito species and insecticide resistance status of An. arabiensis in Itang special woreda (district), Gambella, southwestern Ethiopia. Materials and methods : Adult mosquitoes were sampled from September 2020 to Feburary 2021 using Centers for Disease Control and Prevention (CDC) light trap and Pyrethrum Spray Catch (PSC). Moreover, mosquito larvae were also collected from different breeding sites and reared to adults to assess susceptibility status of populations of An. gambiae s.l. in the study area. Susceptibility tests were conducted on two to three days old non blood fed female An. gambiae s.l using insecticide impregnated papers with deltamethrin (0.05%), alpha-cypermethrin (0.05%), propoxur (0.1%), pirimiphos-methyl (0.25%) and bendiocarb (0.1%) following World Health Organization (WHO) standard susceptibility test procedure. Molecular diagnostics were done for the identification of member species of An. gambiae s.l and detection of knockdown resistance ( kdr ) allele using species specific polymerase chain reaction (PCR) and allele specific PCR. Results : In total, 468 adult mosquitoes were collected from different houses. Culex mosquitoes were the most dominant (80.4%) followed by Anopheles mosquitoes. Three species of Anopheles mosquitoes ( An. coustani, An. pharoensis , and An. gambiae (s.l.)) were identified, of which An. coustani was the dominant (8.1%) species. WHO bioassay tests revealed that the populations of An. gambiae s.l in the study area are resistant against alpha-cypermethrin and deltamethrin whereas, susceptible to bendiocarb, pirimiphos-methyl and propoxur. Out of the total 86 An. gambiae s.l specimens assayed, 79 (92%) successfully amplified and identified as An. arabiensis . West African Kdr (L1014F) mutation was detected with high Kdr allele frequency ranging from 67-88%. Conclusion: The detection of target site mutation, kdr L1014F allele, coupled with the phenotypic resistance against alpha-cypermethrin and deltamethrin call for continuous resistance monitoring.