1. Viral Disease and Epidemiology Research Division, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Japan
2. Pathology and Pathophysiology Research Division, National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), Tsukuba, Japan
3. Institute of Animal Health, National Federation of Agricultural Co-operative Associations, Sakura, Japan
4. Oita Livestock Hygiene Service Center, Oita, Japan