1. Animal Diseases Research Unit, USDA-ARS, 3003 ADBF, Washington State University, Pullman, WA 99164-6630, USA
2. Zoological Society of London, Whipsnade Wild Animal Park, Dunstable, Bedfordshire LU6 2LF, UK
3. North Carolina Veterinary Diagnostic Laboratory System, Rollins Laboratory, Raleigh, NC 27699, USA
4. Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik EH26 0PZ, UK
5. Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164, USA