1. School of Veterinary Medicine, Rakuno-Gakuen University, Ebetsu 069-8501,1
2. National Institute of Infectious Diseases, Shinjuku, Tokyo 162-8640,2
3. Kyoto Prefectural University of Medicine, Kyoto 602-8566,3
4. Public Health Laboratory of Chiba Prefecture, Nitona 666-2, Chuo-ku, Chiba 260-8715,4
5. Shimane Prefectural Institute of Public Health and Environmental Science, Matsue 690-0122,5 and
6. Ohara General Hospital, Fukushima 960-0195,6 Japan