1. Laboratory of Veterinary Microbiology, School of Veterinary Medicine, Kitasato University, Towada, Aomori 034-8628, Japan
2. Aino Animal Hospital, Takao 85-5, Fukuroi, Shizuoka 437-0023, Japan
3. Laboratory of Veterinary Public Health, School of Veterinary Medicine, Kitasato University, Towada, Aomori 034-8628, Japan