1. Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, Iowa 50011, USA
2. Blank Park Zoo, Des Moines, Iowa 50315, USA
3. Department of Infectious Diseases, College of Veterinary Medicine, University of Florida, Gainesville, Florida 32610, USA
4. Division of Comparative Medicine, Johns Hopkins School of Medicine and Department of Medicine, Baltimore, Maryland 21205, USA