1. Department of Medicine and Epidemiology,1
2. Center for Companion Animal Health,2 and
3. Department of Pathology, Microbiology, and Immunology,3 School of Veterinary Medicine, University of California, Davis 95616;
4. Forsyth Institute, Boston, Massachusetts 021154
5. Division of Comparative Medicine, Massachusetts Institute of Technology, Cambridge, Massachusetts 021395; and