Impacts of coinfection on WNV transmission in songbirds

Summary West Nile virus (WNV) is a zoonotic flavivirus that causes the majority of human arboviral disease cases in the United States. WNV transmission is maintained by songbirds and mosquitoes, largely from the genus Culex, with spillover to humans occurring in areas with high rates of competent songbird reservoirs. There is a key need to understand factors that influence the reservoir competence of wild songbirds and their attractiveness to host-seeking Culex mosquitoes. Wild songbirds that are infected with WNV are likely to also harbor infections with other parasites and pathogens, and such co-infections could alter WNV viremia levels in songbirds, attractiveness to mosquitoes, and ultimately, spillover risk to humans. Nonetheless, few animal models exist for studying reservoir competence and mosquito-host interactions in the songbird species that are reservoirs for WNV and ultimately drive spillover into humans. Here we develop a co-infection model using wild-caught house finches, a key amplifying reservoir of WNV. Our long-term goal is to understand the factors that influence songbird WNV competence and attractiveness to host-seeking mosquitoes. The objectives of this study are to experimentally test whether co-infection with a common bacterial pathogen of house finches alters several aspects of songbird reservoir competence: 1) viremia and WNV transmissibility to Culex mosquitoes, and 2) host scent and attractiveness to Culex mosquitoes. Our overarching hypothesis is that bacterial co-infection of songbirds augments WNV spillover risk to humans in two distinct ways: 1) by increasing songbird reservoir competence (e.g., bacterial co-infection increases viremia levels and/or transmission of WNV to mosquitoes) and 2) by mediating chemical interactions between songbirds and mosquitoes (e.g., co-infection alters avian scent profiles and host-seeking behavior of mosquitoes). Two specific aims address our hypothesis: 1) Determine the impact of co-infection on house finch reservoir competence for WNV, and 2) Determine effects of avian infection status on scent profile and mosquito host- seeking behavior. In the first aim, we will perform experimental co-infections using our relevant wild bird model, measuring WNV viremia and transmission to Cx. pipiens mosquitoes in the presence or absence of bacterial co-infection. In the second aim, we will quantify volatile organic compounds produced by birds in the presence of infection or co-infection, and measure mosquito attraction to these scents. Our research is innovative because: 1) it will establish a realistic wild animal model for understanding factors that predict avian competence for WNV, and thus human risk, and 2) it will identify chemical signatures of infected songbirds and subsequent impact on Culex mosquitoes' host-seeking behavior, opening new avenues for early detection and monitoring of WNV in wild populations. Our research is significant because it would represent the first experimental test of whether co-infections of reservoir hosts augment spillover risk to humans for an arbovirus of key human health impact, providing a framework for future studies investigating WNV vectorial capacity.