Insecticide resistance in Anopheles arabiensis from Ethiopia (2012–2016): a nationwide study for insecticide resistance monitoring

• Published in: Malaria Journal
• Main Authors: Louisa A. Messenger, Josephat Shililu, Seth R. Irish, Gedeon Yohannes Anshebo, Alemayehu Getachew Tesfaye, Yemane Ye-Ebiyo, Sheleme Chibsa, Dereje Dengela, Gunawardena Dissanayake, Estifanos Kebede, Endalew Zemene, Abebe Asale, Mekonnen Yohannes, Hiwot Solomon Taffese, Kristen George, Christen Fornadel, Aklilu Seyoum, Robert A. Wirtz, Delenasaw Yewhalaw
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2017
• Subjects: Insecticide resistance; Anopheles arabiensis; Resistance mechanisms; Intensity assays; Malaria; kdr; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/s12936-017-2115-2; https://doaj.org/article/dd879a5f192644d3b030ece0cfcfed2e

Abstract Background Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) remain the cornerstones of malaria vector control. However, the development of insecticide resistance and its implications for operational failure of preventative strategies are of concern. The aim of this study was to characterize insecticide resistance among Anopheles arabiensis populations in Ethiopia and describe temporal and spatial patterns of resistance between 2012 and 2016. Methods Between 2012 and 2016, resistance status of An. arabiensis was assessed annually during the long rainy seasons in study sites from seven of the nine regions in Ethiopia. Insecticide resistance levels were measured with WHO susceptibility tests and CDC bottle bioassays using insecticides from four chemical classes (organochlorines, pyrethroids, organophosphates and carbamates), with minor variations in insecticides tested and assays conducted between years. In selected sites, CDC synergist assays were performed by pre-exposing mosquitoes to piperonyl butoxide (PBO). In 2015 and 2016, mosquitoes from DDT and deltamethrin bioassays were randomly selected, identified to species-level and screened for knockdown resistance (kdr) by PCR. Results Intense resistance to DDT and pyrethroids was pervasive across Ethiopia, consistent with historic use of DDT for IRS and concomitant increases in insecticide-treated net coverage over the last 15 years. Longitudinal resistance trends to malathion, bendiocarb, propoxur and pirimiphos-methyl corresponded to shifts in the national insecticide policy. By 2016, resistance to the latter two insecticides had emerged, with the potential to jeopardize future long-term effectiveness of vector control activities in these areas. Between 2015 and 2016, the West African (L1014F) kdr allele was detected in 74.1% (n = 686/926) of specimens, with frequencies ranging from 31 to 100% and 33 to 100% in survivors from DDT and deltamethrin bioassays, respectively. Restoration of mosquito susceptibility, following ...