1. Kitasato Institute for Life Sciences and Graduate School of Infection Control Sciences, Kitasato University, 5–9–1 Shirokane, Minato-ku, Tokyo 108-8641, Japan
2. Department of Microbiology, School of Pharmaceutical Sciences, Josai University, Sakado, Saitama 350-0295, Japan
3. National Institute of Animal Health, National Agriculture and Food Research Organization, 3–1–5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan