1. Caine Veterinary Teaching and Research Center, University of Idaho, 1020 E. Homedale Road, Caldwell, Idaho 83605, USA
2. United States Department of Agriculture, Agricultural Research Service, Animal Disease Research Unit, Pullman, Washington 99164, USA
3. Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington 99164, USA
4. Idaho Department of Fish and Game, 600 S. Walnut, Boise, Idaho 83707; Idaho Department of Agriculture, 120 Klotz Lane, Boise, Idaho 83707, USA