1. Department of Applied Veterinary Sciences; United Graduate School of Veterinary Sciences; Gifu Gifu 501-1193 Japan
2. Laboratory of Veterinary Microbiology, Faculty of Applied Biological Sciences; Gifu University; Gifu Gifu 501-1193 Japan
3. Epizootic Research Station, Equine Research Institute; The Japanese Racing Association; Tochigi 329-0412 Japan