1. Special Pathogens Laboratory, Department of Virology 1, National Institute of Infectious Diseases, Musashimurayama, Tokyo 208-0011
2. Department of Biomedical Science, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
3. Veterinary Research Department, Research Institute for Tropical Medicine, Department of Health, Muntinlupa City 1770, Philippines