1. United Graduate School of Veterinary Medicine, Yamaguchi University, Yamaguchi 753-8515, Japan
2. Laboratory of Farm Animal Production Medicine, Department of Veterinary Medicine, Faculty of Agriculture, Kagoshima University, Kagoshima 890-0065, Japan
3. Transboundary Animal Disease Control and Research Center, Faculty of Agriculture, Kagoshima University, Kagoshima 890-0065, Japan