1. Department of Medicine and Epidemiology; School of Veterinary Medicine; University of California; Davis CA 95616 USA
2. Department of Pathology; Microbiology and Immunology; School of Veterinary Medicine; University of California; Davis CA 95616 USA
3. Skyline Equine; San Mateo CA 94403 USA
4. W. R. Pritchard; Veterinary Medical Teaching Hospital; School of Veterinary Medicine; University of California; Davis CA 95616 USA