1. Federation of Hokkaido Agricultural Mutual Aid Associations, North 4 West 1–1, Sapporo, Hokkaido 060–0004, Japan
2. Okhotsk Agricultural Mutual Aid Association, Misono 497-1, Kitami, Hokkaido 099–0879, Japan
3. National Institute of Animal Health, 3–1–5 Kan-nondai, Tsukuba, Ibaraki 305–0856, Japan
4. Herd Health Unit, School of Veterinary Medicine, Rakuno Gakuen University, Bunkyodai, Ebetsu, Hokkaido 069–8501, Japan
5. Animal Health Unit, School of Veterinary Medicine, Rakuno Gakuen University, Bunkyodai, Ebetsu, Hokkaido 069–8501, Japan