1. National Institute of Animal Health, 3–1–5 Kannondai, Tsukuba, Ibaraki 305–0856, Japan
2. Tokyo Livestock Hygiene Center, 3–19–4 Fujimi-cho, Tachikawa, Tokyo 190–0013, Japan
3. Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080–8555, Japan