THE MOSQUITO HOLOBIONT: MICROBIOME–VIRUS INTERACTIONS AS DETERMINANTS OF VECTOR COMPETENCE AND ARBOVIRUS EVOLUTION

Abstract

Mosquitoes are not autonomous vectors, but rather a collection of organisms and their surrounding environments (ecological units). The phenotype of mosquitoes is a result of the interactions of the insect host, surrounding microorganisms, invasive viruses, and the surrounding environment. This paper aims to describe the effects on mosquitoes from their bacterial microbiota, fungal associates, insect viruses, and other microbes on mosquito physiology, antiviral immunity, vector competence, and the evolution of arboviruses. From studies done on Aedes mosquitoes, it is shown that certain gut microbes can modify nutrient availability, epithelial barrier integrity, signaling pathways that deal with reactive oxygen, antimicrobial responses, and the crossing of an arbovirus from the gut to the salivary glands. The best example is Wolbachia. Decreases in arbovirus replication have been demonstrated in several laboratory strains. These laboratory strains have also been able to diminish dengue cases in field deployments, though this effect is conditional on strain density, temperature, tissue distribution, and the host genetics. Some insect-specific viruses can inhibit or even reverse replication of arboviruses through superinfection exclusion, but more studies are required for the Arbomycota. The Holobiont approach defines the limits of vector competence. This approach defines vector competence as a system of interacting factors rather than as the traditional fixed trait of a mosquito and a virus. This approach also poses evolutionary questions for the factors that influence arbovirus selection and diversity during transmission. More consistent field studies, longitudinal studies, integrated omics, and greater emphasis on causation over correlation are required.