1. Department of Virology, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
2. Division of Virology, Department of Microbiology and Immunology, Osaka University Graduate School of Medicine, Osaka, Japan
3. Department of Virology, National Institute of Infectious Diseases, Tokyo, Japan
4. Division of Experimental Animal Research, National Institute of Infectious Diseases, Tokyo, Japan