1. Epizootic Research Center, Equine Research Institute, Japan Racing Association, 1400-4 Shiba, Shimotsuke, Tochigi 329-0412, Japan
2. Racehorse Clinic, Ritto Training Center, Japan Racing Association, 1028 Misono, Ritto, Shiga 520-3085, Japan
3. Department of Veterinary Microbiology, Faculty of Agriculture, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8515, Japan