Trends and patterns of insecticide susceptibility of Anopheles gambiae between 2015 and 2020: implications for malaria vector control interventions in Ghana.

BACKGROUND: The distribution and use of insecticide treated nets (ITNs) and indoor residual spraying (IRS) are the two main insecticide-based tools that have been scaled up in Ghana. Although insecticide resistance to different insecticides have been reported in parts of Ghana, there is little information on the status and extent of resistance in malaria vectors across different areas in the country. There was, therefore, a need to generate annual geographically specific insecticide resistance data to assist in the development of insecticide resistance management strategies in Ghana. This study presents five years data on monitoring of four classes of insecticides.

METHODS: Standard World Health Organization (WHO) insecticide susceptibility tube assays were carried out annually on adult female Anopheles gambiae reared from immature stages in 30 sentinel sites across Ghana each year from 2015 to 2020. Insecticide papers impregnated with seven insecticides in four classes were used for assays in the selected sites. PCR was performed to identify mosquito species and detect knock down resistance, kdr-west (L1014F) and acetylcholinesterase, ace-1 G119S gene mutations in forty randomly selected mosquitoes per site.

RESULTS: High resistance to pyrethroids and DDT was detected in all the sites with a decrease in susceptibility over the years. The susceptibility of carbamates and organophosphates reduced in all the sites over the 5 years. Anopheles gambiae sensu stricto (s.s.) and Anopheles coluzzii represented the two-main species of the complex living in sympatry mostly in the southern sentinel sites, with Anopheles arabiensis in smaller numbers in the northern Sahelian sites. The target site resistance frequency was significantly higher for the L1014F compared to the G119S with variations across the sites.

CONCLUSION: Findings showed that resistance to deltamethrin, permethrin (pyrethroids), DDT (organochlorine) malathion and pirimiphos-methyl (organophosphates) and bendiocarb and propoxur (carbamates) was widespread in Ghana. There is high frequency of L1014F alleles (kdr-west) in all the sites with marginal increase for G119S ace-1 mutations. This highlights the need for continuous monitoring of the insecticide resistance of An. gambiae sensu lato in the country to ensure informed decision-making on resistance management strategies and choice of insecticides for malaria vector control in Ghana.