Climate and landscape drivers of a mosquito-borne pathogen in an iconic game bird in the eastern and upper midwestern USA

The ruffed grouse (Bonasa umbellus) is a non-migratory upland game bird that inhabits young and mature forests in the USA and Canada. Population indices in some portions of its range, particularly the eastern USA, have been in decline since the arrival of West Nile virus (WNV), a mosquito-borne Flavivirus. Subsequent experimental research suggested that WNV may cause morbidity and/or mortality in up to 90% of grouse, which had similar clinicopathologic findings to naturally-infected grouse. Additionally, WNV serosurveys in Pennsylvania revealed low seroprevalence concurrent with elevated vector indices. To further elucidate aspects of WNV epidemiology in ruffed grouse, we tested hunter-collected filter paper strips for anti-WNV antibodies in 15 states during fall-winter, 2018-2022. Annual total seroprevalence ranged from 12.0% in 2019-2020 to 17.9% in 2021-2022. We assessed for associations between county-level WNV seroprevalence and large-scale climate, environmental, and landscape variables through Bayesian multilevel modeling, accounting for spatial autocorrelation. The top model suggested that WNV seroprevalence was positively correlated with summer precipitation; the second most supported model suggested similar findings of positive correlation between WNV seroprevalence and spring precipitation. Management strategies should prioritize understanding factors that influence mosquito-borne pathogen transmission in conjunction with providing more forested habitat of high quality for ruffed grouse to optimize survival in the face of WNV and other challenges.