1. Division of Bacterial and Parasitic DiseaseNational Institute of Animal Health, National Agriculture and Food Research Organization Tsukuba Ibaraki 305‐0856 Japan
2. The United Graduate School of Veterinary SciencesGifu University Gifu Gifu 501‐1193 Japan
3. Iwate Prefectural Chuo Livestock Hygiene Service Center Takizawa Iwate 020‐0605 Japan
4. Aichi Prefectural Chuo Livestock Hygiene Service Center Okazaki Aichi 444‐0805 Japan