Evidence of multiple pyrethroid resistance mechanisms in the malaria vector Anopheles gambiae sensu stricto from Nigeria.
Pyrethroid insecticide resistance in Anopheles gambiae sensu stricto is a major concern to malaria vector control programmes. Resistance is mainly due to target-site insensitivity arising from a single point mutation, often referred to as knockdown resistance (kdr). Metabolic-based resistance mechanisms have also been implicated in pyrethroid resistance in East Africa and are currently being investigated in West Africa. Here we report the co-occurrence of both resistance mechanisms in a population of An. gambiae s.s. from Nigeria. Bioassay, synergist and biochemical analysis carried out on resistant and susceptible strains of An. gambiae s.s. from the same geographical area revealed >50% of the West African kdr mutation in the resistant mosquitoes but <3% in the susceptible mosquitoes. Resistant mosquitoes synergized using pyperonyl butoxide before permethrin exposure showed a significant increase in mortality compared with the non-synergized. Biochemical assays showed an increased level of monooxygenase but not glutathione-S-transferase or esterase activities in the resistant mosquitoes. Microarray analysis using the An. gambiae detox-chip for expression of detoxifying genes showed five over-expressed genes in the resistant strain when compared with the susceptible one. Two of these, CPLC8 and CPLC#, are cuticular genes not implicated in pyrethroid metabolism in An. gambiae s.s, and could constitute a novel set of candidate genes that warrant further investigation.
Awolola
T S
TS
Nigerian Institute of Medical Research, Yaba, Lagos, Nigeria. awololas@hotmail.com
Oduola
O A
OA
Strode
C
C
Koekemoer
L L
LL
Brooke
B
B
Ranson
H
H
D000818:Animals; D000852:Anopheles / Q000187:drug effects / Q000235:genetics*; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides / Q000494:pharmacology; D007814:Larva / Q000187:drug effects / Q000235:genetics*; D008288:Malaria / Q000235:genetics / Q000635:transmission; D009032:Mosquito Control; D009549:Nigeria; D020411:Oligonucleotide Array Sequence Analysis; D017354:Point Mutation / Q000235:genetics*; D011722:Pyrethrins / Q000494:pharmacology
D007306:Insecticides; D011722:Pyrethrins