1. Viral Diseases and Epidemiology Research Division, National Institute of Animal Health, Tsukuba, Ibaraki, Japan
2. Department of Infection Biology, Division of Biomedical Science, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
3. Western Center for Livestock Hygiene Service, Higashihiroshima, Hiroshima Prefecture, Hiroshima, Japan