1. Department of Veterinary Pathology; School of Veterinary Medicine, Rakuno Gakuen University; 582 Bunkyodai-Midorimachi Ebetsu Hokkaido 069-8501 Japan
2. Department of Veterinary Virology; School of Veterinary Medicine, Rakuno Gakuen University; 582 Bunkyodai-Midorimachi Ebetsu Hokkaido 069-8501 Japan
3. Shadai Corporation; Hayakita Hokkaido 053-1432 Japan
4. Department of Virology; Research Institute for Microbial Disease, Osaka University; Suita Osaka 565-0871 Japan