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

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Résumé

Abstract
Background 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.
Methods 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.
Results 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.
Conclusions 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.

Mots-clés

Malaria, Anopheles gambiae s.l., Insecticide, Synergist, Resistance, SIR, EIR, Burkina Faso