1. Den-en-chofu Animal Hospital, 2-1-3 Denenchofu, Ota-ku, Tokyo 145-0071, Japan
2. Laboratory of Veterinary Microbiology, Joint Faculty of Veterinary Medicine, Yamaguchi University, 1677-1 Yoshida-shi, Yamaguchi 753-8515, Japan
3. Laboratory of Veterinary Pathology, Faculty of Veterinary Medicine, Okayama University of Science, 1-3 Ikoino-oka, Imabari-shi, Ehime 794-8555, Japan
4. Department of Veterinary Science, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan