1. Department of Veterinary Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan
2. Department of Virology, National Institute of Animal Health, 3-1-1 Kannondai, Tsukuba 305-0856, Japan
3. Kyushu Research Station, National Institute of Animal Health, 1702 Chuzan, Kagoshima 891-0105, Japan