Molecular detection and maternal transmission of a bacterial symbiont Asaia species in field-caught Anopheles mosquitoes from Cameroon

Background: Malaria control relies mainlyon insecticide-based tools. However, the effectiveness of these tools is threatened by widespread insecticide resistance in malaria vectors, highlighting the need for alternative control approaches. The endosymbiont Asaia has emerged as a promising candidate for paratransgenic control of malaria, but its biology and genetics still need to be further analyzed across Africa. Here, we investigated the prevalence of Asaia and its maternal transmission in the natural population of Anopheles mosquitoes in Cameroon. Methods: Indoor-resting adult mosquitoes belonging to four species (An. coluzzii, An. arabiensis, An. funestus and An. gambiae) were collected from eight localities across Cameroon from July 2016 to February 2020. PCR was performed on the Asaia-specific 16S ribosomal RNA gene, and samples positive by PCR for Asaia were confirmed by Sanger sequencing and phylogenetic analysis. The vertical transmission of Asaia was investigated by screening F-1 mosquitoes belonging to F(0)Asaia-positive females. Results: A total of 895 mosquitoes were screened. We found 43% (384) Asaia infection prevalence in four mosquito species. Phylogenetic analysis revealed that Asaia from Cameroon clustered together with the strains of Asaia isolated from other parts of the world. In addition, seven nucleotide sequence variants were found with low genetic diversity (pi = 0.00241) and nucleotide sequence variant diversity (Hd = 0.481). Asaia was vertically transmitted with high frequency (range from 42.5 to 100%). Conclusions: This study provides field-based evidence of the presence of Asaia in Anopheles mosquitoes in Cameroon for exploitation as a symbiont in the control of malaria in sub-Saharan Africa.

Automated summary

This study investigated the prevalence and maternal transmission of Asaia in natural populations of Anopheles mosquitoes in Cameroon. Results showed that Asaia was vertically transmitted at a high frequency among four mosquito species, providing valuable information for using Asaia in the control of malaria in sub-Saharan Africa.