1. Animal Diseases Research Unit, USDA-Agricultural Research Service, Pullman, Washington 99164, USA
2. Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington 99164, USA
3. US Geological Survey, New Mexico Cooperative Fish and Wildlife Research Unit, Las Cruces, New Mexico 88003, USA
4. Prairie Diagnostic Service, Saskatoon, Saskatchewan, S7N 5B4, Canada