title: High level of resistance in the mosquito Anopheles gambiae to pyrethroid insecticides and reduced susceptibility to bendiocarb in north-western Tanzania.
abstract: BACKGROUND
  To control malaria in Tanzania, two primary vector control interventions are being scaled up: long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). The main threat to effective malaria control is the selection of insecticide resistance. While resistance to pyrethroids, the primary insecticide used for LLINs and IRS, has been reported among mosquito vectors in only a few sites in Tanzania, neighbouring East African countries are recording increasing levels of resistance. To monitor the rapidly evolving situation, the resistance status of the malaria vector Anopheles gambiae s.l to different insecticides and the prevalence of the kdr resistance allele involved in pyrethroid resistance were investigated in north-western Tanzania, an area that has been subject to several rounds of pyrethroid IRS since 2006.
  
  
  METHODS
  Household collections of anopheline mosquitoes were exposed to diagnostic dosages of pyrethroid, DDT, and bendiocarb using WHO resistance test kits. The relative proportions of An. gambiae s.s and Anopheles arabiensis were also investigated among mosquitoes sampled using indoor CDC light traps. Anophelines were identified to species and the kdr mutation was detected using real time PCR TaqMan assays.
  
  
  RESULTS
  From the light trap collections 80% of An. gambiae s.l were identified as An. gambiae s.s and 20% as An. arabiensis. There was cross-resistance between pyrethroids and DDT with mortality no higher than 40% reported in any of the resistance tests. The kdr-eastern variant was present in homozygous form in 97% of An. gambiae s.s but was absent in An. arabiensis. Anopheles gambiae s.s showed reduced susceptibility to the carbamate insecticide, bendiocarb, the proportion surviving WHO tests ranging from 0% to 30% depending on season and location.
  
  
  CONCLUSIONS
  Anopheles gambiae s.s has developed phenotypic resistance to pyrethroids and DDT and kdr frequency has almost reached fixation. Unlike in coastal Tanzania, where the ratio of An. gambiae s.s to An. arabiensis has decreased in response to vector control, An. gambiae s.s persists at high frequency in north-western Tanzania, probably due to selection of pyrethroid resistance, and this trend is likely to arise in other areas as resistance spreads or is subject to local selection from IRS or LLINs.
authors: Department of Disease Control, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK. natacha.protopopoff@lshtm.ac.uk
authors: Natacha
authors: N
authors: Protopopoff
authors: Johnson
authors: J
authors: Matowo
authors: Robert
authors: R
authors: Malima
authors: Reginald
authors: R
authors: Kavishe
authors: Robert
authors: R
authors: Kaaya
authors: Alexandra
authors: A
authors: Wright
authors: Philippa A
authors: PA
authors: West
authors: Immo
authors: I
authors: Kleinschmidt
authors: William
authors: W
authors: Kisinza
authors: Franklin W
authors: FW
authors: Mosha
authors: Mark
authors: M
authors: Rowland
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects*; D005260:Female; D005819:Genetic Markers; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D059645:Mutation Rate; D048448:Phenylcarbamates / Q000494:pharmacology*; D015995:Prevalence; D011722:Pyrethrins / Q000494:pharmacology*; D013636:Tanzania
chemical_list: D005819:Genetic Markers; D007306:Insecticides; D048448:Phenylcarbamates; D011722:Pyrethrins; C007725:bendiocarb
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