1. Division of Virology, Department of Microbiology and Immunology, Osaka University Graduate School of Medicine, Suita 565-0871, Japan
2. Department of Virology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan
3. Department of Virology, Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8558, Japan