1. Epidemiological Research Team, National Institute of Animal Health, Ibaraki 305-0856, Japan
2. Animal Health Division, Food Safety and Consumer Affairs Bureau Ministry of Agriculture, Forestry and Fisheries, Tokyo 100-8950, Japan
3. Nobeoka Livestock Hygiene Service Center, Miyazaki 882-0803, Japan
4. Department of Planning and General Administration, National Institute of Animal Health, Ibaraki 305-0856, Japan