1. US Department of Agriculture; Agricultural Research Service; Animal Disease Research Unit; Pullman WA 99164-7030 USA
2. Department of Veterinary Microbiology and Pathology/Washington Animal Disease Diagnostic Laboratory; College of Veterinary Medicine; Washington State University; Pullman WA 99164 USA
3. Department of Veterinary Clinical Studies; College of Veterinary Medicine; Washington State University; Pullman WA 99164 USA