1. Laboratory of Wildlife Biology and Medicine, Graduate School of Veterinary Medicine, Hokkaido University, Kita 18 Nishi 9, Sapporo, Hokkaido 060–0818, Japan
2. Department of Bacteriology-I, National Institute of Infectious Diseases, 1–23–1 Toyama, Shinjuku-ku, Tokyo 162–8640, Japan
3. Laboratory of Infectious Diseases, Graduate School of Veterinary Medicine, Hokkaido University, Kita 18 Nishi 9, Sapporo, Hokkaido 060–0818, Japan