Fatal West Nile Virus Infection in Free-Ranging Greater Sage Grouse (Centrocercus urophasianus) in Wyoming, Montana, and Alberta
American Association of Zoo Veterinarians Conference 2004
Todd E. Cornish1, DVM, PhD, DACVP; Walter E. Cook2, DVM, PhD, DACVPM; Terry E. Creekmore3, MS; Elizabeth S. Williams1, DVM, PhD, DACVP; David E. Naugle4, PhD; Brett L. Walker4, MS; Cameron L. Aldridge5, MS; Trent K. Bollinger6, DVM, DVSc; Margo J. Pybus7, PhD; Thomas J. Christiansen8, MS
1Wyoming State Veterinary Laboratory, University of Wyoming, Laramie, WY, USA; 2Wyoming Game and Fish Department, Laramie, WY, USA; 3Wyoming Department of Health, Laramie, WY, USA; 4University of Montana, Missoula, MT, USA; 5University of Alberta, Edmonton, AB, Canada; 6Canadian Cooperative Wildlife Health Centre, Saskatoon, SK, Canada; 7Alberta Sustainable Resources Development-Fish and Wildlife, Edmonton, AB, Canada; 8Wyoming Game and Fish Department, Green River, WY, USA
Abstract
Greater sage grouse (Centrocercus urophasianus) is a declining species native to sagebrush habitats of western North America. Historically widespread, the species has disappeared from much of its original range, with an estimated total population decline of 45–80% and local declines of 17–92%.1,2 Loss and degradation of nesting and brood-rearing habitat from human change is thought to be the single most important factor leading to fragmentation, reduction, and extirpation of populations. These changes also increase the risks to sage grouse populations from other factors, including diseases like West Nile virus (WNV).
In the summer of 2003, WNV was diagnosed as the cause of mortality for 24 free-ranging sage grouse from Wyoming and Montana and five free-ranging grouse from Alberta. At necropsy, significant gross lesions were not observed in most birds. Consistent microscopic lesions included acute necrosis in many organs, including spleen, kidney, heart, and adrenal gland, without significant inflammation. West Nile virus infection was confirmed by real-time PCR and immunohistochemistry in all birds, and by virus isolation in select birds. In contrast to most other species in the order Galliformes, sage grouse appear to be quite susceptible to fatal infection with WNV.3
Data collected from three marked populations of sage grouse in Wyoming and Montana indicate that WNV infection was responsible for a 25% decrease in annual survivorship in each of these populations. Serologic surveys performed on birds from two marked populations of sage grouse in Wyoming and Montana and on marked birds from Alberta and hunter-killed birds from areas in Wyoming that experienced WNV sage grouse mortalities demonstrated that 0/111 birds had serum-neutralizing antibodies against WNV. These findings are not conclusive, but at least suggest that few (if any) sage grouse survived WNV infection in the summer of 2003.
In spring of 2004 an experimental trial will be performed at the University of Wyoming to determine the outcome of WNV infection in sage grouse. Level and duration of viremia, development of clinical signs, survivorship, and the potential for contact transmission will be investigated. Expanded field investigations into the epidemiology and pathogenesis of WNV in the field, including arthropod vector studies, also will be performed at several sites in Wyoming and Montana in 2004 and 2005, with participation by investigators from the University of Montana, the University of Wyoming, Montana State University, the Bureau of Land Management, and the USDA, ARS, Arthropod-Borne Animal Disease Research Laboratory.
Literature Cited
1. Connelly JW, Schroeder MA, Sands AR, Braun CE. Guidelines to manage sage grouse populations and their habitats. Wildlife Society Bulletin. 2000;28:967–985.
2. Connelly JW, Braun CE. Long-term changes in sage grouse Centrocercus urophasianus populations in western North America. Wildlife Biology. 1997;3/4:229–234.
3. McLean RG, Ubico SR, Bourne D, Komar N. West Nile virus in livestock and wildlife. Current Topics in Microbiology and Immunology. 2002;267:271–308.