The L1014F Kdr mutation is associated with a higher prevalence and load of the Plasmodium-blocking symbiont Microsporidia MB In Anopheles Gambiae s.l. In Benin

Introduction: The Plasmodium transmission-blocking endosymbiont Microsporidia MB was previously identified in Anopheles gambiae s.l., but its association with the carriage of the genotypes of the L1014F kdr mutation, as well as the ecological factors driving its geographical distribution remain understudied. 

Methods: Adult mosquitoes were field-collected using human landing catches (HLCs) across 60 villages in the Covè, Ouinhi, and Zangnanado communes of southern Benin. After morphological identification, a sub-sample of An. gambiae s.l. were molecularly speciated, and genotypied for the L1014F kdr mutation by Polymerase Chain Reaction (PCR). Enzyme-Linked Immunosorbent Assay (ELISA) and qPCR were also used to assess infection with Plasmodium falciparum sporozoites and Microsporidia MB, respectively. The environmental variables that drive the habitat suitability for Microsporidia MB were also assessed using Maximum Entropy (MaxEnt) modelling. 

Results: The An. gambiae complex (N = 1040) was composed of 93.7% An. coluzzii, 4.4% An. gambiae s.s., 0.2% An. gambiae s.s./coluzzii hybrids, while the rest failed to amplify. Infection prevalence with Microsporidia MB was 1.6% (95% CI: 0.7–3.3) in An. coluzzii and 2.2% (95% CI: 0.1–13.2) in An. gambiae s.s. The P. falciparum sporozoite rate was 2% (95% CI: 1.2–3.1, N = 974) in An. coluzzii, and null in An. gambiae s.s. (N = 46). None of the mosquitoes infected with Microsporidia MB were infected with P. falciparum. The frequency of the L1014F kdr mutation was 75.1% (95% CI: 73.1–76.9) in An. coluzzii and 91.3% (95% CI: 83.1–95.9) in An. gambiae s.s. Microsporidia MB was absent in kdr-SS mosquitoes but was present in low proportions in both kdr-RS and kdr-RR mosquitoes (1.9%, 95% CI: 0.6–5.1). The mean load of Microsporidia MB DNA was higher in kdr-RR (23.23 ng/µl, 95% CI: 18.77–28.48) compared to kdr-RS (10.13 ng/µl, 95% CI: 7.36–13.91) mosquitoes. The elevation and soil contributed to explain, at 78% and 20% respectively, the habitat suitability for Microsporidia MB. 

Conclusion: In this study, we demonstrated that An. gambiae s.l. mosquitoes bearing the L1014F kdr resistant allele was associated with a higher prevalence and load of Microsporidia MB than their susceptible counterparts. Moreover, the geographical distribution of Microsporidia MB was found to be influenced by certain environmental conditions, which warrant further large-scale investigations.