title: Synergist bioassays: A simple method for initial metabolic resistance investigation of field Anopheles gambiae s.l. populations.
abstract: Metabolic resistance and the potential role of permeability-glycoprotein (P-gp) efflux pumps were investigated in a pyrethroid-resistant wild Anopheles gambiae s.l. Tiassalé population, using WHO susceptibility assays with deltamethrin (0.05%), with and without pre-exposure to synergists. The synergists used included an inhibitor of P-glycoprotein efflux pumps (verapamil), an inhibitor of esterases (EN 16-5), and an inhibitor of P450s and esterases (piperonyl butoxide). Pre-exposure to verapamil followed by deltamethrin led to a slight but non-significant (P=0.59) increase in mortality relative to exposure to deltamethrin alone (64.5% versus 69.2%). Similarly, pre-exposure to EN 16-5 yielded a non-significant increase in mortality (to 76.6%; P=0.85) but a significant increase in the knock down rate (from 48.3% to 78.7%; P<0.01). Pre-exposure with PBO caused a significant increase in mortality (to 93.1%; P<0.001) and knockdown rate (100%; P<0.001), which related to a 2.9 fold decrease in the resistance level. The results provide evidence that metabolic resistance mechanisms are present within the assessed mosquito population. The decrease in time to knock down of this population with deltamethrin following exposure to EN16-5 and PBO is of particular relevance to vector control, where quick knock down is a highly desired characteristic. The suspected resistance mechanisms present in this population merit further investigation through biochemical and molecular analyses for full resistance profile characterization. Bioassays with synergists can provide a quick and easy basis for initial characterization of resistant mosquito populations, without the need of preserved specimens, expensive equipment and substrates or specialized expertise.
authors.affiliation: Centre Suisse de Recherches Scientifiques en Côte d'Ivoire (CSRS), 01 BP1303, Abidjan 01, Cote d'Ivoire. Electronic address: ms.chouaibou@gmail.com.
authors.forename: Mouhamadou
authors.initials: M
authors.lastname: Chouaïbou
authors.affiliation: Vestergaard Frandsen, Chemin de Messidor 5-7, CH-1006, Lausanne, Switzerland.
authors.forename: Georgina Bingham
authors.initials: GB
authors.lastname: Zivanovic
authors.affiliation: Vestergaard Frandsen, Waiyaki Way, ABC Place, PO Box 66889-00800, Nairobi, Kenya.
authors.forename: Tessa B
authors.initials: TB
authors.lastname: Knox
authors.affiliation: Vestergaard Frandsen, Chemin de Messidor 5-7, CH-1006, Lausanne, Switzerland.
authors.forename: Helen Pates
authors.initials: HP
authors.lastname: Jamet
authors.affiliation: Centre Suisse de Recherches Scientifiques en Côte d'Ivoire (CSRS), 01 BP1303, Abidjan 01, Cote d'Ivoire.
authors.forename: Bassirou
authors.initials: B
authors.lastname: Bonfoh
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000378:metabolism; D001681:Biological Assay / Q000379:methods*; D065607:Cytochrome P-450 Enzyme Inhibitors / Q000494:pharmacology; D004950:Esterases / Q000037:antagonists & inhibitors; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D009570:Nitriles / Q000494:pharmacology*; D010882:Piperonyl Butoxide / Q000494:pharmacology; D011722:Pyrethrins / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D065607:Cytochrome P-450 Enzyme Inhibitors; D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017180:decamethrin; D014700:Verapamil; D004950:Esterases; D010882:Piperonyl Butoxide
keywords: Anopheles gambiae; Esterases; Insecticide resistance; Metabolic resistance; P-glycoprotein efflux pump; P450s