1. Laboratories of Veterinary Public Health, Department of Veterinary Medicine; College of Bioresource Sciences, Nihon University; Fujisawa Kanagawa 252-8510 Japan
2. Preventive Veterinary Medicine and Animal Health, Department of Veterinary Medicine; College of Bioresource Sciences, Nihon University; Fujisawa Kanagawa 252-8510 Japan
3. Veterinary Surgery, Department of Veterinary Medicine; College of Bioresource Sciences, Nihon University; Fujisawa Kanagawa 252-8510 Japan
4. First Department of Oral Surgery; School of Dentistry at Matsudo, Nihon University; Matsudo Chiba 271-8587 Japan
5. Department of Virology I; National Institute of Infectious Diseases; Shinjuku-ku Tokyo 162-8640 Japan