1. Tokachi Livestock Hygiene Service Center, 59-6 Kisen, Kawanishi, Obihiro, Hokkaido 089-1182, Japan
2. National Institute of Animal Health, National Agriculture and Research Organization, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan
3. Shiga Prefectural Livestock Technology Promotion Center, 695 Yamamoto, Hino, Gamo, Shiga 529-1651, Japan
4. Hokkaido Research Station, National Institute of Animal Health, 4 Hitsujigaoka, Toyohira, Sapporo, Hokkaido 062-0045, Japan