Insecticide Resistance Status and Mechanisms in Aedes Mosquitoes in Ghana

Abstract

Background Aedes mosquitoes are vectors of arboviral diseases such as dengue and yellow fever, which are of major public health concern. Vector control, which relies mainly on the use of insecticides, is the main intervention for arboviral disease control. However, Aedes mosquitoes are developing resistance to several classes of insecticides. In Ghana, data about the mechanisms involved in insecticide resistance in Aedes mosquitoes is lacking. Aim of Study The aim of this study is to investigate the insecticide resistance status of Aedes populations and the mechanisms involved in selected urban and suburban settings in Ghana. Methodology This is a cross-sectional study carried out in urban sites (Accra and Tema) and suburban sites (Ada and Navrongo) in Ghana. Aedes larvae were collected in all the study sites and raised to adults in the insectary. Phenotypic resistance was determined using the WHO susceptibility test. Resistant and susceptible Aedes mosquitoes were subjected to morphological identification. Insecticide target site genes were amplified and sequenced to detect mutations conferring genotypic resistance in Aedes populations. A synergist assay was also used to determine the involvement of the metabolic enzymes (specifically oxidases) in the phenotypic resistance observed across the sites. Results The results showed high phenotypic resistance to Dichlorodiphenyltrichloroethane (DDT) and pyrethroids, with percentage mortalities ranging from 11.3% to 75.8% for those exposed to DDT and 62.5% to 88.8% for those exposed to pyrethroids (deltamethrin and permethrin) in all sites. Aedes mosquitoes collected from Tema were found to be resistant to all the classes of insecticides tested (pyrethroids, organophosphates, organochloride and carbamates). Suspected resistance to carbamate and organophosphates was also detected in some sites. All resistant and susceptible Aedes mosquitoes that were morphologically identified were confirmed to be Aedes aegypti (100%). High frequency of point mutations at the voltage-gated sodium channel (F1534C and V1016I) were detected in both resistant and susceptible Aedes aegypti mosquitoes from all sites. Pre-exposure to Piperonyl Butoxide (PBO) significantly enhanced the susceptibility of Aedes to almost all insecticides tested. This may be an indicator that metabolic enzymes (oxidases) may be partially or fully involved in the development of resistance in some Aedes populations. Conclusion These findings suggest that resistance profiles in Aedes aegypti mosquitoes vary across sites in Ghana and seem to be increasing rapidly especially among the pyrethroids and organochlorides (DDT). DDT resistance is widespread across all sites tested. The phenotypic resistance observed are likely to be mediated by multiple resistant mechanisms (genetic and metabolic mechanisms) per the findings obtained. Thus, there is a need to explore ways to effectively control resistant Aedes populations to help control arboviral diseases in Ghana.