Role of physico-chemical environmental factors in the emergence and development of insecticides resistant mosquito in Nigeria
The aim of this study is to investigate the role of physico-chemical environmental factors present in mosquito breeding ecologies as sources of selection pressure for the emergence and development of insecticides resistance in Anopheles gambiae from Northern Nigeria.Prospecting for, and sampling of An. gambiae larvae was carried out from many breeding sites in towns and villages spread out across Kano and Jigawa states of Northern Nigeria. The breeding sites visited and sampled were grouped into three study zones according to the type of human related activities taking place around the mosquito breeding environments. Larval densities (per litre of breeding water) and water chemistry analysis were carried out from all the breeding sites visited. Detoxification enzymes; Cytochrome P450, Glutathione S-transferases and Esterases as well as glutathione assays were carried out on the three life stages of the sampled An. gambiae using the relevant assay protocols. The results showed that the levels of the physical environmental factors; pH, temperature, conductivity, transparency,dissolved oxygen and biological oxygen demand did not vary significantly (p<0.05) across the three studied zones. The levels of the chemical environmental factors; total dissolved solids, sulphate, phosphate, nitrite and nitrate ions were significantly (p0.05) higher in study zone A compare to the other two zones, while carbon content and oil and grease were significantly (p<0.05) distributed in study C than the other two zones. Likewise, the activity of P450s was higher in study zone C while those of GST and CEs were significantly (p<0.05)higher in study zone A compared to the other two zones. Additionally, most of the chemical environmental factors were significantly (p<0.05) associated with larval density and activities of the detoxification enzymes. Oxidized glutathione (GSSG) levels were also highly associated (p<0.05) with the activities of the three enzymes studies. A deduced model of multivariate regression established all the chemical environmental factors and some of the physical environmental factors as producing a combined effect on larval density and detoxification enzymes activities. These observations showed that An. gambae emerging from breeding sites located in study zones A & C may have, through adaptive tolerance,acquired the necessary detoxification machinery that could allow it to rapidly develop resistance to various classes of insecticides. Finally, the contribution and implications of the findings in this study to the challenges facing vector control as a tool in malaria management,specifically, the contribution to the underlying mechanism of insecticides resistance and the various factors selecting for resistance development in An. gambiae were discussed.
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