1. National Institute of Animal Health,3–1–5 Kannondai, Tsukuba, Ibaraki 305–0856, Japan
2. Tokachi Livestock Hygiene Service Center, Kawanishicho, Obihiro, Hokkaido 089–1182, Japan
3. Jouhoku Livestock Hygiene Service Center, Shikamoto-cho, Yamaga, Kumamoto 861–0304, Japan
4. Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080–8555, Japan