title: Pyrethroid resistance in Anopheles gambiae, in Bomi County, Liberia, compromises malaria vector control.
abstract: BACKGROUND
  Long Lasting Insecticidal Nets (LLIN) and Indoor Residual Spraying (IRS) have both proven to be effective malaria vector control strategies in Africa and the new technology of insecticide treated durable wall lining (DL) is being evaluated. Sustaining these interventions at high coverage levels is logistically challenging and, furthermore, the increase in insecticide resistance in African malaria vectors may reduce the efficacy of these chemical based interventions. Monitoring of vector populations and evaluation of the efficacy of insecticide based control approaches should be integral components of malaria control programmes. This study reports on entomological survey conducted in 2011 in Bomi County, Liberia.
  
  
  METHODS
  Anopheles gambiae larvae were collected from four sites in Bomi, Liberia, and reared in a field insectary. Two to five days old female adult An gambiae s.l. were tested using WHO tube (n=2027) and cone (n=580) bioassays in houses treated with DL or IRS. A sample of mosquitoes (n=169) were identified to species/molecular form and screened for the presence of knock down resistance (kdr) alleles associated with pyrethroid resistance.
  
  
  RESULTS
  Anopheles gambiae s.l tested were resistant to deltamethrin but fully susceptible to bendiocarb and fenithrothion. The corrected mortality of local mosquitoes exposed to houses treated with deltamethrin either via IRS or DL was 12% and 59% respectively, suggesting that resistance may affect the efficacy of these interventions. The presence of pyrethroid resistance was associated with a high frequency of the 1014F kdr allele (90.5%) although this mutation alone cannot explain the resistance levels observed.
  
  
  CONCLUSIONS
  High prevalence of resistance to deltamethrin in Bomi County may reduce the efficacy of malaria strategies relying on this class of insecticide. The findings highlight the urgent need to expand and sustain monitoring of insecticide resistance in Liberian malaria vectors, evaluate the effectiveness of existing interventions and develop appropriate resistance management strategies.
authors.affiliation: The MENTOR Initiative, Crawley, United Kingdom. emmanuel.temu@gmail.com
authors.forename: Emmanuel A
authors.initials: EA
authors.lastname: Temu
authors.forename: Caroline
authors.initials: C
authors.lastname: Maxwell
authors.forename: Godwil
authors.initials: G
authors.lastname: Munyekenye
authors.forename: Annabel F V
authors.initials: AF
authors.lastname: Howard
authors.forename: Stephen
authors.initials: S
authors.lastname: Munga
authors.forename: Silas W
authors.initials: SW
authors.lastname: Avicor
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Poupardin
authors.forename: Joel J
authors.initials: JJ
authors.lastname: Jones
authors.forename: Richard
authors.initials: R
authors.lastname: Allan
authors.forename: Immo
authors.initials: I
authors.lastname: Kleinschmidt
authors.forename: Hilary
authors.initials: H
authors.lastname: Ranson
mesh_terms: D000483:Alleles; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000235:genetics; D001681:Biological Assay; D002648:Child; D005260:Female; D005838:Genotype; D005843:Geography; D006801:Humans; D007303:Insect Vectors / Q000187:drug effects* / Q000235:genetics; D007305:Insecticide Resistance / Q000187:drug effects* / Q000235:genetics; D057148:Insecticide-Treated Bednets; D007814:Larva / Q000187:drug effects / Q000235:genetics; D007988:Liberia; D008288:Malaria / Q000469:parasitology* / Q000517:prevention & control*; D009032:Mosquito Control; D009154:Mutation / Q000235:genetics; D009570:Nitriles / Q000633:toxicity; D011722:Pyrethrins / Q000633:toxicity*; D014944:World Health Organization
chemical_list: D009570:Nitriles; D011722:Pyrethrins; C017180:decamethrin