Increased avian diversity is associated with lower incidence of West Nile virus in both human and bird populations

West Nile virus is most commonly spread among birds by mosquito vectors, and is a disease of significant public health, veterinary, and conservation concern. As the proportion of infected birds increases in populations, the risk of humans being bitten and infected also increases. As bird species vary in their competency as disease hosts, ecological theory predicts that increasing avian species diversity will result in lower overall levels of the virus and lower risks to humans. We provide broad geographic evidence, from the Eastern US, that increased species diversity of avian communities is associated with decreased incidence of West Nile virus infection in both human and bird populations. Further, we indicate that particular avian families are high risk indicators for human infection. A lower relative abundance of corvids (crows and jays) and a higher relative abundance of invasive Old World sparrows (house sparrows, Passer domesticus) are particular indicators of increased human infection. This pattern runs contrary to common perception and may relate to the ecology and disease response of these species. Crows die quickly from West Nile infection and roost further from humans than house sparrows, rendering crows a lower risk to human infection. However, house sparrows survive for longer periods while infected with West Nile and are often closely associated with humans. Therefore, our analyses indicate that current disease prevention and surveillance plans should include a perspective that accounts for community structure and species ecology and not solely rely on species-specific disease response to predict disease threat.