1. Western Center for Livestock Hygiene Service, Hiroshima Prefecture, 1-15 Saijogojo-cho, Higashi-Hiroshima, Hiroshima 739-0013, Japan
2. Obihiro University of Agriculture and Veterinary Medicine, 2-11 Inada, Obihiro, Hokkaido 080-8555, Japan
3. National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan