1. Graduate School of Infection Control Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
2. O̅mura Satoshi Memorial Institute, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
3. Tokyo New Drug Research Laboratories, Pharmaceutical Business Unit, Kowa Company, Ltd., 2-17-43 Noguchicho, Higashimurayama, Tokyo 189-0022, Japan