Potential population impacts of West Nile virus on Pennsylvania ruffed grouse (Bonasa umbellus)

Since its arrival to North America in 1999, West Nile virus (WNV) has had unprecedented adverse effects on the health of native birds across numerous taxa. In Pennsylvania, WNV was first documented statewide in 2002, soon... [ view full abstract ]

Since its arrival to North America in 1999, West Nile virus (WNV) has had unprecedented adverse effects on the health of native birds across numerous taxa. In Pennsylvania, WNV was first documented statewide in 2002, soon after which precipitous population declines were observed in Pennsylvania ruffed grouse (Bonasa umbellus), an important gamebird species and the State bird. Statewide, grouse populations have not since recovered. The present study assessed the potential impacts of WNV on Pennsylvania ruffed grouse populations through integrating laboratory- and field-derived data. Methods included both experimental infections of juvenile grouse and serology (plaque reduction neutralization test) on field-collected blood samples. Grouse were susceptible to experimentally-induced WNV morbidity and had moderate viremia titers (mean peak: 10e6.9 plaque forming units/ml serum). Viremia was generally detectable for 4-6 days, and for up to 8 days in birds euthanized due to illness. Forty percent (4/10) were euthanized on 7-8 days post-inoculation (DPI) due to clinical disease (weight loss, dehydration, limb paresis); lesions in these birds included severe non-suppurative myocarditis, myocardial degeneration, and minimal encephalitis. Among subclinically-infected grouse that survived to 14 DPI, encephalitis was more severe and half (3/6) also had severe myocarditis, suggesting that encephalitis is more likely a chronic manifestation of WNV in grouse, and that longer-term survival may have been compromised in most of these birds. All inoculated grouse surviving to 14 DPI seroconverted based on virus neutralization assays performed on serum and Nobuto strips. No in-contact sham-inoculated controls had evidence of infection. Ongoing blood collections from hunter-harvested Pennsylvania ruffed grouse via Nobuto strips reveal a WNV seroprevalence of 12.3% (25/204), including seropositive birds in 15 counties. Collectively, experimental challenge data and field-derived serologic data provide insight into the distribution and extent of WNV prevalence and the potential impacts of WNV on Pennsylvania ruffed grouse.