1. William R. Pritchard Veterinary Medical Teaching Hospital; University of California; Davis; CA; 95616; USA
2. Department of Medicine and Epidemiology; School of Veterinary Medicine; University of California; Davis; CA; 95616; USA
3. PO Box 4812; North Rocks; NSW; 2151; Australia
4. Department of Pathology, Microbiology and Immunology; University of California; Davis; CA; 95616; USA