1. Livestock Hygiene Service Centre of Hidaka; Shizunai Hokkaido 056-0003 Japan
2. Epizootic Research Centre; Equine Research Institute; Japan Racing Association; Shimotsuke Tochigi 329-0412 Japan
3. Department of Animal Hygiene; School of Veterinary Medicine and Animal Sciences; Kitasato University; Towada Aomori 034-8628 Japan