1. Laboratory of Veterinary Public Health; Department of Veterinary Medical Science; Graduate School of Agricultural and Life Sciences; University of Tokyo; 1-1-1 Yayoi Bunkyo Tokyo 113-8657 Japan
2. Department of Veterinary Science; National Institute of Infectious Diseases; 1-23-1 Toyama Shinjuku Tokyo 162-8640 Japan
3. Major Track of Applied Veterinary Science; Doctoral Course of the United Graduate School of Veterinary Sciences; Gifu University; 1-1 Yanagido Gifu 501-1193 Japan
4. Department of Integrated Science in Physics and Biology College of Humanities and Sciences; Nihon University; 3-25-40 Sakurajosui Setagaya Tokyo 156-8550 Japan