1. Research Institute for Animal Science in Biochemistry & Toxicology, 3–7–11 Hashimotodai, Midori-ku, Sagamihara, Kanagawa 252–0132, Japan
2. Animal Quarantine Service of the Ministry of Agriculture, Forestry and Fisheries of Japan, 11–1 Haramachi, Isogo-ku, Yokohama, Kanagawa 235–0008, Japan
3. Research Team for Zoonotic Diseases, National Institute of Animal Health, 3–1–5 Kannondai, Tsukuba, Ibaraki 305–0856, Japan
4. Present address: NAS Laboratory Co., Ltd., 680 Tokura, Tomisato, Chiba 286–0212, Japan