1. Safety Research Team, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba 305-0856, Japan
2. Division of Microbial Diseases, Department of Infectious Diseases, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan
3. Division of Livestock Industry, Department of Agriculture, Forestry and Fisheries, Miyagi Prefectural Government, 3-8-1 Honcho, Aoba-ku, Sendai, Miyagi 980-8570, Japan
4. Center for Animal Disease Control and Prevention, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan
5. Epidemiological Research Team, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan