1. From the Animal Diseases Research Unit, USDA-Agricultural Research Service (Traul, Taus, Li), and the Washington Animal Disease Diagnostic Laboratory and Department of Veterinary Microbiology and Pathology (Oaks, Rurangirwa, Baszler), Washington State University, Pullman, WA 99164; the Wyoming State Veterinary Laboratory (O'Toole), University of Wyoming, Laramie, WY 82070.