Light Pollution Increases West Nile Virus Competence in a Ubiquitous Passerine Reservoir Species

One sentence summaryLight pollution increases host infectiousness.\n\nAbstractLight pollution is a growing problem, but its impacts on infectious disease risk have not been considered. Previous research has revealed that dim light at night (dLAN) dysregulates various immune functions and biorhythms, which hints that dLAN could change the risk of disease epidemics. Here, we demonstrate that dLAN enhances infectiousness of the house sparrow (Passer domesticus), an urban-dwelling avian host of West Nile virus (WNV). Sparrows exposed to dLAN maintained viral titers above the transmission threshold to a biting vector (105 plaque-forming units) for two days longer than controls but did not die at higher rates. A mathematical model revealed that such effects could increase WNV outbreak potential by ~41%. dLAN likely affects other host and vector traits relevant to transmission, so additional research is needed to advise management of zoonotic diseases in light polluted areas.