1. School of Veterinary Medicine, Azabu University, Sagamihara, Kanagawa 252-5201, Japan
2. Faculty of Bioresources and Environmental Science, Ishikawa Prefectural University, Nonoichi, Ishikawa 921-8836, Japan
3. Research and Education Center for Prevention of Global Infectious Diseases of Animals, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan
4. Department of Pathology, National Institute of Infectious Diseases, Shinjuku, Tokyo 162-8640, Japan
5. Cooperative Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan
6. Center for Animal Disease Control, University of Miyazaki, Miyazaki 889-2192, Japan
7. Department of Virology II, National Institute of Infectious Diseases, Musashimurayama, Tokyo 208-0011, Japan