Malaria control relies mainly on insecticide-based tools. The endosymbiont Asaia has emerged as a promising candidate for paratransgenic control of malaria, even if its biology and genetics still need to be further analyzed across Africa.
This is why Grace Maffo Tatsinkou investigated the prevalence and the genetic diversity of Asaia and its maternal transmission in the natural population of Anopheles mosquitoes in Cameroon. In this study, 895 mosquitoes were screened. The researcher 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. What is important to retain is that, Asaia infects all mosquito species but this varies according to mosquito species.
Furthermore, the results obtained show variability in infection rates between localities in different species of Anopheles. A situation well explained when she noted: “ the heterogeneous routes in transmission including feeding on flowers, breeding site, and horizontal and vertical dissemination events. The highest infection rates of Asaia were observed at Elon, Elende and Obout, which are all located in the forest region. This highest infection rate could be attributed to the abundance of plants and breeding sites.” Asaia has been shown to be a promising candidate for paratransgenic control of malaria. This is as a result of its negative effect on the development of Plasmodium at different stages. In this study, the author focused on the effect of Asaia on Plasmodium in natural populations. The data obtained show that, in field Anopheles populations of Mibellon, the presence of Asaia did not affect the infection of mosquitoes by plasmodium. These conclusions are in accord with the results of a recent study demonstrating that Asaia and Wolbachia do not influence plasmodium infection in natural populations.
As it is well known, Asaia has been presented as a promising candidate for alternative control of malaria. This study provides preliminary evidence of the circulation of Asaia in malaria vectors in Cameroon. The predominance of a nucleotide sequence variant in all the mosquito species suggests the feasibility of a paratransgenic control approach via the bioengineering of Asaia in malaria vectors. These data provide important baseline information towards developing potential strategies by exploring the possibility of utilizing them for malaria control. In order to carry out this study, mosquitoes were collected in eight localities in Cameroon, namely Gounougou in the Northern Region; Tibati and Mibellon in Adamaoua Region; Mangoum in West Region; Bankeng, Elon, Elende and Obout in the Centre Region; from July 2016 to February 2020.
The samples from Mibellon, Gounougou and Bankeng were collected in the rainy season, while those from Elende, Elon, Obout, Mangoum and Tibati were collected in the dry season. Indoor resting female mosquitoes were collected using electric aspirators between 06:00 a.m. and 09:00 a.m. The collected mosquitoes were transported to the insectary at the Centre for Research in Infectious Diseases (CRID), Yaounde, where they were morphologically identified following morphological identification keys for Afrotropical anopheline mosquitoes. According to National Malaria Control Program (NMCP), an estimated 23.6% of consultation in health centres, 68.7% of deaths in children under 5 years, and 16.9% of deaths in pregnant women are malaria-related cases. Malaria transmission in Cameroon is principally driven by species of the Anopheles Gambiae complex. In this regard, insecticide-based vector control interventions, such as long-lasting insecticidal nets (LLINs) and Indoor Residual Spraying (IRS), have been the cornerstone of malaria prevention efforts. The widespread insecticide and drug resistance in mosquitoes and parasites respectively weakens malaria control efforts across Africa, including Cameroon. Therefore, investigating the genetic diversity and the maternal transmission of natural Asaia strains in Anopheles populations would allow a greater understanding of how this bacterium could influence malaria transmission in field populations as well as in the identification of candidate strains for paratransgenesis.