Editorial: Microbiota: A Consequential Third Wheel in the Mosquito-Pathogen Relationship

Mosquitoes are by far the most important vectors of human disease. There are hundreds of millions of cases of dengue annually, while Chikungunya and Zika have recently caused major outbreaks. Malaria remains a major driver of poverty in sub-Saharan Africa where it is responsible for about 400,000 deaths each year. In addition, about 50 million cases of lymphatic filariasis still occur annually. The microbial communities harbored by mosquitoes have been the focus of great scientific interest since the discovery of their significant impact on disease transmission, via their influence on mosquito physiology and permissiveness to infection. In the 1990s and 2000s, the gut microbiota was found to limit parasitic infection in Anopheles malaria vector mosquitoes in experiments that used antibiotic treatments. It was subsequently demonstrated that Wolbachia endosymbionts could protect their insects hosts against viruses. In the 2010s, as high-throughput DNA sequencing became increasingly available to researchers, a more thorough description of the mosquito microbiota composition was generated and correlated to environmental or experimental parameters. Toward the end of the 2010s many more functional studies on mosquito/microbiota interactions were being carried out, and several countries had started to experiment with Wolbachia-infected mosquitoes as a public health measure to limit dengue transmission. These advances have culminated in a widespread appreciation that vector-pathogen interactions must be investigated in the context of a consequential third player, the microbiota. In the article collection “Microbiota: A Consequential Third Wheel in the Mosquito-Pathogen Relationship,” we gathered state-of-the-art research on the microbiota of mosquitoes, including bacteria and eukaryotic microbes. This collection examines the interplay between three types of research in the field: functional characterization of host-microbe and microbe-microbe interactions, description of the microbiota system composition, and the design of microbiota-based tools to block disease transmission. These three aims are being advanced in parallel and are indeed interdependent, as functional characterizations identify specific attributes that can be used in the field if the system is better understood, whether functionally or taxonomically, while observations from applied research in the field bring novel questions to the basic research directions and a good description of the microbiota gives essential clues about how host-microbe associations work and how interventions may affect microbiota systems and what the consequences of this may be.