title: Spatial and Temporal Trends in Insecticide Resistance among Malaria Vectors in Chad Highlight the Importance of Continual Monitoring.
abstract: A longitudinal Anopheles gambiae s.l. insecticide resistance monitoring programme was established in four sentinel sites in Chad 2008-2010. When this programme ended, only sporadic bioassays were performed in a small number of sites.
  
  
  
  WHO diagnostic dose assays were used to measure the prevalence of insecticide resistance to 0.1% bendiocarb, 4% DDT, 0.05% deltamethrin, 1% fenitrothion, and 0.75% permethrin in the main malaria vectors at the beginning and end of the malaria transmission season for three years 2008-2010, with subsequent collections in 2011 and 2014. Species and molecular identification of An. gambiae M and S forms and kdr genotyping was performed using PCR-RLFP; circumsporozoite status was assessed using ELISA.
  
  
  
  Between 2008 and 2010, significant changes in insecticide resistance profiles to deltamethrin and permethrin were seen in 2 of the sites. No significant changes were seen in resistance to DDT in any site during the study period. Testing performed after the period of routine monitoring had ended showed dramatic increases to DDT and pyrethroid resistance in 3 sites. No resistance to organophosphate or carbamate insecticides was detected. An. arabiensis was the predominate member of the An. gambiae complex in all 4 sites; adult collections showed temporal variation in species composition in only 1 site. Kdr analysis identified both 1014F and 1014S alleles in An. gambiae S only. Circumsporozoite analysis showed the highest vector infection rates were present in Donia, a site with extensive use of agricultural insecticides.
  
  
  
  During the monitoring gap of four years, significant changes occurred in resistance prevalence in 3 of the 4 sites (p = <0.001), endangering the efficacy of currently implemented malaria control interventions. Significant changes in insecticide resistance profiles and a lack of kdr resistance alleles in adult populations highlight the urgent need for comprehensive entomological monitoring to be implemented and sustained in country.
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
authors.forename: Geraldine Marie
authors.initials: GM
authors.lastname: Foster
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Coleman
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
authors.forename: Edward
authors.initials: E
authors.lastname: Thomsen
authors.affiliation: Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
authors.forename: Hilary
authors.initials: H
authors.lastname: Ranson
authors.affiliation: Programme National de Lutte contre le Paludisme, N'Djamena, Chad.
authors.forename: Elise
authors.initials: E
authors.lastname: Yangalbé-Kalnone
authors.affiliation: Programme National de Lutte contre le Paludisme, N'Djamena, Chad.
authors.forename: Tchomfienet
authors.initials: T
authors.lastname: Moundai
authors.affiliation: Programme National de Lutte contre le Paludisme, N'Djamena, Chad.
authors.forename: Israel
authors.initials: I
authors.lastname: Demba Kodindo
authors.affiliation: Programme National de Lutte contre le Paludisme, N'Djamena, Chad.
authors.forename: Amen
authors.initials: A
authors.lastname: Nakebang
authors.affiliation: Programme National de Lutte contre l'Onchocercose, Ministère de la Santé Publique, N'Djamena, Chad.
authors.forename: Adoum
authors.initials: A
authors.lastname: Mahamat
authors.affiliation: Programme National de Lutte contre la Trypanosomiase Humaine Africaine, Ministère de la Santé Publique, N'Djamena, Chad.
authors.forename: Mallaye
authors.initials: M
authors.lastname: Peka
authors.affiliation: Programme National de Lutte contre le Paludisme, N'Djamena, Chad.
authors.forename: Clement
authors.initials: C
authors.lastname: Kerah-Hinzoumbé
mesh_terms: D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000235:genetics; D004199:Disease Vectors; D019476:Insect Proteins / Q000235:genetics; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D008137:Longitudinal Studies; D008288:Malaria / Q000175:diagnosis* / Q000188:drug therapy* / Q000401:mortality
chemical_list: D019476:Insect Proteins; D007306:Insecticides