# Insecticide resistance and malaria transmission indicators in Anopheles gambiae s.l. in Bobo-Dioulasso, Burkina Faso: implications for vector control strategies

## TL;DR

This study in Burkina Faso found high insecticide resistance in malaria-carrying mosquitoes, but some insecticides still work, highlighting the need for updated control strategies.

## Contribution

The study provides new insights into insecticide resistance patterns and malaria transmission dynamics in Anopheles gambiae populations in Bobo-Dioulasso.

## Key findings

- High resistance to dichlorodiphenyltrichloroethane and pyrethroids was observed, with evidence of metabolic resistance mechanisms.
- Anopheles arabiensis was the dominant malaria vector, contributing 91.2% of infectious bites with a high sporozoite infection rate.
- Bendiocarb and pirimiphos-methyl showed susceptibility in most localities, suggesting potential for continued use in vector control.

## Abstract

In the context of intensified malaria control efforts in Burkina Faso, this study assessed i) the insecticide resistance status of Anopheles gambiae sensu lato and ii) key entomological indicators of malaria transmission in Bobo-Dioulasso.

World Health Organization–standard susceptibility bioassays were conducted on Anopheles populations collected from six neighborhoods (Kua, Sarfalao, Sabaribougou, Dogona, Farakan and Kodeni). The bioassays tested six insecticides organochlorines (4%dichlorodiphenyltrichloroethane), organophosphates (1.25% pirimiphos-methyl), pyrethroids (0.75%permethrin, 0.05% deltamethrin, 0.05% alpha-cypermethrin), and carbamates (0.1% bendiocarb). Synergist bioassays using piperonyl butoxide (PBO) were also performed to investigate metabolic resistance mechanisms, and Plasmodium infection rates were determined via Polymerase Chain Reaction.

Overall, data revealed high resistance levels to dichlorodiphenyltrichloroethane and pyrethroids, which are associated with moderate or higher frequencies of knockdown resistance mutations (L995F and L995S). Fortunately, a susceptibility to bendiocarb and pirimiphos-methyl was found in the majority of localities. The restoration of pyrethroid susceptibility following piperonyl butoxide pre-exposure suggests the involvement of metabolic resistance mechanisms. Analysis of 622 specimens from the Anopheles gambiae complex revealed a predominance of An. arabiensis (90.8%), followed by An. gambiae s.s. and An. coluzzii. Sporozoite infection rates varied by species, reaching 45% in An. coluzzii, 27.4% in An. arabiensis, and 16.2% in An. gambiae s.s. The overall entomological inoculation rate (EIR) was estimated at 10.6 infectious bites per person during the study period. Anopheles arabiensis contributed most of these bites (91.2%), highlighting its central role in malaria transmission in Bobo-Dioulasso.

Despite insecticide resistance, Anopheles populations exhibited high Plasmodium infection rates, indicating ongoing transmission. These findings emphasize the urgent need for sustained entomological surveillance and resistance management to guide and optimize insecticide-based malaria control strategies.