1. Laboratory of Veterinary Virology, Department of Pathobiology, School of Veterinary Medicine, Rakuno Gakuen University, 582 Bunkyoudai-Midorimachi, Ebetsu, Hokkaido 069-8501, Japan
2. Shadai Stallion Station, 275 Hayakita-Genbu, Abira-cho, Yufutsu-gun, Hokkaido 059-1501, Japan