Temperature affects viral kinetics and vectorial capacity of Aedes aegypti mosquitoes co-infected with Mayaro and Dengue viruses

Increasing global temperatures and unpredictable climatic extremes have contributed to the spread of vector-borne diseases. The mosquito Aedes aegypti is the main vector of multiple arboviruses that negatively impact human health, mostly in low socioeconomic areas of the world. Co-circulation and co-infection of these viruses in humans have been increasingly reported; however, how vectors contribute to this alarming trend remains unclear. Here, we examine single and co-infection of Mayaro virus (-D strain, Alphavirus) and dengue virus (serotype 2, Flavivirus) in Ae. aegypti adults and cell lines at two constant temperatures, moderate (27{degrees}C) and hot (32{degrees}C), to quantify vector competence and the effect of temperature on infection, dissemination and transmission, including on the degree of interaction between the two viruses. Both viruses were primarily affected by temperature but there was a partial interaction with co-infection. Dengue virus quickly replicates in adult mosquitoes, with a tendency for higher titers in co-infected mosquitoes at both temperatures and mosquito mortality was more severe at higher temperatures in all conditions. For dengue, and to a lesser extent Mayaro, vector competence and vectorial capacity were higher at hotter temperature in co- vs single infections and was more evident at earlier timepoints (7 vs 14 days post infection). The temperature-dependent phenotype was confirmed in vitro by faster cellular infection and initial replication at higher temperatures for dengue but not for Mayaro virus. Our study suggests that contrasting kinetics of the two viruses could be related to their intrinsic thermal requirements, where alphaviruses thrive better at lower temperatures compared to flaviviruses, but further studies are necessary to clarify the role of co-infection at different and variable temperature regimes. Author summaryGlobal warming is having devastating consequences for the environment, and a cause of concern is the increase in local abundance and geographic range of mosquitoes and the associated viruses they transmit. This study explores how temperature affects the mosquitos ability to survive and potentially spread two viruses, Mayaro and dengue, in single or co-infections. We found that Mayaro virus was not clearly affected by temperature or the presence of dengue infection. In contrast, dengue virus showed higher infection and potential for higher transmission in mosquitoes kept at high temperatures, and this trend was stronger in co-infections compared to single infections. Mosquito survival consistently decreased at high temperatures. We hypothesize the differences observed for dengue virus are due to the faster growth and viral activity in the mosquito at hotter temperatures, a pattern not observed for Mayaro virus. More studies under different temperature regimes are needed to clarify the role of co-infection.