Molecular Analysis Of Mechanisms And Identification Of Factors Of Pyrethroid Resistance In Anopheles Gambiae Sensu Lato In Southwestern Nigeria And Southern Benin Republic

ABSTRACT

The development of resistance to insecticides by Anopheles mosquitoes continues to threaten the success of malaria control programmes in West Africa. Local data on mechanisms and factors causing resistance in the region are scanty. This study was designed to investigate the environmental factors and mechanisms implicated in resistance to pyrethroids by Anopheles gambiae in southwestern Nigeria and southern Benin Republic.  Larvae of Anopheles mosquito were collected in 2007 from 19 localities in the six states of southwestern Nigeria and 18 localities in the seven divisions of southern Benin and reared to adults. These were identified morphologically and with Polymerase Chain Reactions (PCR). They were also bioassayed for susceptibility to pyrethroids. Molecular characterisation of pyrethroid resistant phenotypes was carried out using PCR and microarray analyses of the expressed genes. Dissolved Oxygen (DO) and pH were determined using a digital multipurpose meter while physical appearances of breeding sites were assessed visually. Xenobiotic factors such as Spilled Engine Oil (SEO) and agricultural pesticides that might contribute to the emergence of resistance in Anopheles populations were examined through bioassay. Associations between pyrethroid resistance with environmental factors and molecular profiles of Anopheles were evaluated using Chi square. A. gambiae complex genotyped in Nigeria comprised of 73.6 % A. arabiensis and 26.3 % A. gambiae sensu stricto; while those genotyped in Benin were 92.9 % A. gambiae s.s. and 7.0 % A. melas. Pyrethroid resistance in Nigeria and Benin were recorded in 68.4 % and 94.4 % of the localities examined respectively. Breeding sites contaminated with SEO (B-SEO) or Pesticide Residues (B-PR) had low DO (B-SEO = 13.4 ± 1.5 mg/l, BPR=12.2 ± 1.7 mg/l), the Non-contaminated Breeding sites (B-NC) had higher levels of DO (B-NC=33.1 ± 2.3) and mainly produced pyrethroid-susceptible Anopheles (p