Microsporidia MB (MB), a promising biological control agent, suppresses Plasmodium falciparum transmission in Anopheles mosquitoes. This study examined the spatial distribution of MB infection in natural populations of An. gambiae s.l. mosquitoes collected in Nigeria and Niger Republic, and its association with insecticide susceptibility in the mosquitoes. Microsporidia MB has wide geographic distribution across Nigeria and Niger Republic. The overall prevalence of MB in F₀ mosquitoes was 12.25% (95% CI: 7.76–16.75%); 25 mosquitoes out of 204 were positive. Geographic variation was observed, with a higher prevalence (5/15 mosquitoes) in Ebonyi State (33.33%, CI: 9.48–57.19%, Fisher’s exact test, p = 0.008). Infection rates were higher in An. coluzzii mosquitoes (21/133 mosquitoes), estimated at 15.79% (CI: 9.59–21.99%) compared to An. gambiae s.s. mosquitoes (4/71), with approximately 5.63% (CI: 0.27–11.00%, χ² = 4.44; df = 1, p = 0.035). Resistant mosquitoes had a significantly higher prevalence of MB infection than susceptible mosquitos at 28.57% (CI: 16.74–40.40%) with an odds ratio of 3.33 (CI: 1.23–9.03, p = 0.017). These findings suggests that MB can be exploited as an alternative for vector control in Nigeria and Niger, but its possible association with pyrethroid resistance suggests that it should be taken into account as a potential confounder when designing insecticide resistance management strategies.

Background: Microsporidia MB (MB), a promising biological control agent suppresses Plasmodium falciparum transmission in Anopheles mosquitoes. Methods: This study examined the spatial distribution of MB infection in natural populations of An. gambiae s.l. mosquitoes collected in Nigeria and Niger Republic, and its potential modulation of insecticide susceptibility in the Anopheles mosquitoes. Results: The overall prevalence of MB in F₀ mosquitoes was 12.25% (95% CI: 7.76%-16.75%); 25 mosquitoes out of 204 were positive. Geographic variation was observed, with a higher prevalence (5/15 mosquitoes) in Ebonyi State (33.33%, 95% CI: 9.48%-57.19%, Fisher's exact test, p = 0.008). Infection rates were higher in An. coluzzii mosquitoes (21/133 mosquitoes), estimated at 15.79% (95% CI: 9.59%-21.99%) compared to An. gambiae s.s. mosquitoes (4/67), approximately 5.63% (95% CI: 0.27%-11.00%), χ² = 4.44; df = 1, p = 0.035)]. Resistant mosquitoes had a significantly higher prevalence of MB infection at 28.57% (95% CI: 16.74%-40.40%) and OR of 3.33 (95% CI: 1.23-9.03, p = 0.017) compared with susceptible mosquitoes. Conclusion: MB has wide geographic distribution across Nigeria and Niger Republic. An. coluzzii and resistant mosquitoes are more infected with this fungi. Understanding the geographic and species-specific infection patterns and implication in insecticide resistance could guide targeted vector control strategies using this biological agent.