1. Department of Infection Control Science, Faculty of Medicine, Juntendo University, Tokyo 113-8421, Japan
2. Department of Veterinary Hygiene, Veterinary School, Nippon Veterinary and Life Science University, 1-7-1 Kyounan, Musashino, Tokyo 180-8602, Japan
3. Awachuo Animal Hospital, 60 Yawata, Tateyama, Chiba 294-0047, Japan
4. Department of Veterinary Medicine, Faculty of Applied Biological Sciences, Gifu University, Gifu 501-1193, Japan