1 Department of Veterinary Medicine, Faculty of Veterinary Medicine, Okayama University of Science, 1-3 Ikoino-oka, Imabari, Ehime, 794-8555, Japan. n-akashi@vet.ous.ac.jp.
2 Tottori Prefectural Kurayoshi Livestock Hygiene Service Center, 2-132 Seidanicho, Tottori, Tottori, 682-0017, Japan.
3 National Institute of Animal Health, National Agriculture and Food Research Organization (NARO), 3-1-5 Kannondai, Tsukuba, Ibaraki, 305-0856, Japan.
4 Department of Veterinary Science, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-58 Rinku-oraikita, Izumisano, Osaka, 598-8531, Japan.