1. Laboratory of Veterinary Epizootiology, Department of Veterinary Medicine, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-0880, Japan
2. Present address: Okinawa Zoo and Museum Foundation, 5-7-1 Goya, Okinawa-shi, Okinawa 904-0021, Japan