title: Increasing insecticide resistance in Anopheles funestus and Anopheles arabiensis in Malawi, 2011-2015.
abstract: BACKGROUND
  Susceptibility of principal Anopheles malaria vectors to common insecticides was monitored over a 5-year period across Malawi to inform and guide the national malaria control programme.
  
  
  METHODS
  Adult blood-fed Anopheles spp. and larvae were collected from multiple sites in sixteen districts across the country between 2011 and 2015. First generation (F1) progeny aged 2-5 days old were tested for susceptibility, using standard WHO procedures, against pyrethroids (permethrin and deltamethrin), carbamates (bendiocarb and propoxur), organophosphates (malathion and pirimiphos-methyl) and an organochlorine (DDT).
  
  
  RESULTS
  Mortality of Anopheles funestus to deltamethrin, permethrin, bendiocarb and propoxur declined significantly over the 5-year (2011-2015) monitoring period. There was wide variation in susceptibility to DDT but it was not associated with time. In contrast, An. funestus exhibited 100% mortality to the organophosphates (malathion and pirimiphos-methyl) at all sites tested. There was reduced mortality of Anopheles arabiensis to deltamethrin over time though this was not statistically significant. However, mortality of An. arabiensis exposed to permethrin declined significantly over time. Anopheles arabiensis exposed to DDT were more likely to be killed if there was high ITN coverage in the mosquito collection area the previous year. There were no other associations between mosquito mortality in a bioassay and ITN coverage or IRS implementation. Mortality of An. funestus from four sites exposed to deltamethrin alone ranged from 2 to 31% and from 41 to 94% when pre-exposed to the synergist piperonyl butoxide followed by deltamethrin. For permethrin alone, mortality ranged from 2 to 13% while mortality ranged from 63 to 100% when pre-exposed to PBO.
  
  
  CONCLUSIONS
  Pyrethroid resistance was detected in An. funestus and An. arabiensis populations across Malawi and has worsened over the last 5 years. New insecticides and control strategies are urgently needed to reduce the burden of malaria in Malawi.
authors.affiliation: Malaria Alert Centre, Malawi College of Medicine, Chichiri, P/Bag 360, Blantyre 3, Malawi. tmzilahowa@mac.medcol.mw.
authors.forename: Themba
authors.initials: T
authors.lastname: Mzilahowa
authors.affiliation: Malaria Alert Centre, Malawi College of Medicine, Chichiri, P/Bag 360, Blantyre 3, Malawi.
authors.forename: Martin
authors.initials: M
authors.lastname: Chiumia
authors.affiliation: Malaria Alert Centre, Malawi College of Medicine, Chichiri, P/Bag 360, Blantyre 3, Malawi.
authors.forename: Rex B
authors.initials: RB
authors.lastname: Mbewe
authors.affiliation: Malaria Alert Centre, Malawi College of Medicine, Chichiri, P/Bag 360, Blantyre 3, Malawi.
authors.forename: Veronica T
authors.initials: VT
authors.lastname: Uzalili
authors.affiliation: Malaria Alert Centre, Malawi College of Medicine, Chichiri, P/Bag 360, Blantyre 3, Malawi.
authors.forename: Madalitso
authors.initials: M
authors.lastname: Luka-Banda
authors.affiliation: Malaria Alert Centre, Malawi College of Medicine, Chichiri, P/Bag 360, Blantyre 3, Malawi.
authors.forename: Anna
authors.initials: A
authors.lastname: Kutengule
authors.affiliation: Malaria Alert Centre, Malawi College of Medicine, Chichiri, P/Bag 360, Blantyre 3, Malawi.
authors.forename: Don P
authors.initials: DP
authors.lastname: Mathanga
authors.affiliation: Community Health Services Unit, National Malaria Control Programme, Ministry of Health, Lilongwe, Malawi.
authors.forename: Doreen
authors.initials: D
authors.lastname: Ali
authors.affiliation: Community Health Services Unit, National Malaria Control Programme, Ministry of Health, Lilongwe, Malawi.
authors.forename: John
authors.initials: J
authors.lastname: Chiphwanya
authors.affiliation: Community Health Services Unit, National Malaria Control Programme, Ministry of Health, Lilongwe, Malawi.
authors.forename: John
authors.initials: J
authors.lastname: Zoya
authors.affiliation: Community Health Services Unit, National Malaria Control Programme, Ministry of Health, Lilongwe, Malawi.
authors.forename: Shadreck
authors.initials: S
authors.lastname: Mulenga
authors.affiliation: WHO Country-office, Lilongwe, Malawi.
authors.forename: Wilfred
authors.initials: W
authors.lastname: Dodoli
authors.affiliation: President's Malaria Initiative, United States Agency for International Development, Lilongwe, Malawi.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Bergeson-Lockwood
authors.affiliation: President's Malaria Initiative, Centers for Disease Control and Prevention, Lilongwe, Malawi.
authors.forename: Peter
authors.initials: P
authors.lastname: Troell
authors.affiliation: Division of Parasitic Diseases and Malaria, Centers for Diseases Control and Prevention, Atlanta, GA, USA.
authors.forename: Jessica
authors.initials: J
authors.lastname: Oyugi
authors.affiliation: Division of Parasitic Diseases and Malaria, Centers for Diseases Control and Prevention, Atlanta, GA, USA.
authors.forename: Kim
authors.initials: K
authors.lastname: Lindblade
authors.affiliation: Division of Parasitic Diseases and Malaria, Centers for Diseases Control and Prevention, Atlanta, GA, USA.
authors.forename: John E
authors.initials: JE
authors.lastname: Gimnig
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects*; D001681:Biological Assay; D005260:Female; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects; D008295:Malawi; D000072138:Mosquito Vectors / Q000187:drug effects*; D015995:Prevalence; D011722:Pyrethrins / Q000494:pharmacology; D016019:Survival Analysis
chemical_list: D007306:Insecticides; D011722:Pyrethrins
keywords: Anopheles funestus; Anopheles gambiae; Insecticide resistance; Malawi; Pyrethroid resistance