Adaptation of Mayaro virus to urban mosquitoes

PROJECT ABSTRACT The alphavirus Mayaro virus (MAYV) is a mosquito-borne human pathogen that causes febrile illness and arthralgia in Latin America but has not produced widespread outbreaks like related chikungunya virus (CHIKV). MAYV infections probably occur after exposure to infected forest-dwelling vector mosquito species. Previous outbreaks of both CHIKV and Venezuelan equine encephalitis virus (VEEV, another alphavirus) were mediated by viral mutations that confer adaptation to urban-abundant mosquito species, which facilitated forest-to-city spillover promoting urban epidemics. One reason MAYV has not produced widespread epidemics may be that anthropophilic urban Aedes (Ae.) aegypti and Ae. albopictus are incompetent MAYV vectors. Multiple laboratory vector competence studies from different continents show MAYV poorly infects both species where doses required for infection are at the higher end or above human viremia levels. Epidemics could result if MAYV adapts to increase infection and transmission at lower ingested doses in either urban Ae. species since an increase in mosquito susceptibility means that infected people with low viremias are infectious to mosquitoes, which can potentiate mosquito-human-mosquito cycling. In earlier studies, we used serial passaging and sequencing to identify an envelope (E) gene CHIKV mutant know to lower the oral infectious dose and increase transmission by Ae. albopictus. This work demonstrates the power of experimental evolution to retrospectively identify epidemiologically relevant alphavirus mutations. However, similar studies have not been performed for MAYV. The goal of this project is to assess the potential for Mayaro virus to adapt to urban mosquito vectors using an experimental evolution approach. We hypothesize that MAYV can adapt via serial Ae. mosquito and alternating Ae.-mouse-Ae. passage to 1) increase infection of and transmission by Ae. aegypti and Ae. albopictus mosquitoes at lower ingested doses; 2) maintain transmissibility during alternating cycling; and 3) accrue E gene mutations that augment Ae. infection and transmission. These hypotheses will be tested by assessing the potential for MAYV adaptation to and sustained cycling via urban Ae. by (Aim 1A): evaluating fitness of MAYV serially passaged in Ae. aegypti and albopictus mosquitoes, (Aim 1B): evaluating fitness of MAYV alternately passaged between Ae. and mice, and (Aim 1C): identifying mutations that arise during MAYV passage and evaluating mutant fitness in mosquitoes. This project represents the first experimental evolution studies for MAYV in Ae.. Understanding the potential for adaptation is important to define the risk of future MAYV outbreaks mediated by novel vector use. Knowledge of mutations that confer MAYV adaptation to Ae. can be used to define mechanisms of increased mosquito infection and transmission, for inclusion in MAYV vaccine development, and as a target for genomic surveillance. The use of experimental evolution to predict virus adaptation can lead to a paradigm shift to enable proactive measures to prevent virus epidemics.