1. Department of Infectious Diseases, Faculty of Medicine; Oita University; Yufu Oita 879-5593 Japan
2. Center for International Collaborative Research; Nagasaki University; Nagasaki Nagasaki 852-8523 Japan
3. Institute of Tropical Medicine; Nagasaki University; Nagasaki Nagasaki 852-8523 Japan
4. Division of Molecular Virology, Department of Microbiology; Graduate School of Medicine University of the Ryukyus; Nishihara Okinawa 903-0125 Japan