1. Division of Pathology; National Institute of Health Sciences; 1-18-1, Kamiyoga, Setagaya-ku Tokyo 158-8501 Japan
2. Laboratory of Veterinary Public Health, Department of Veterinary Medicine, College of Bioresource Science; Nihon University; 1866, Kameino Fujisawa-city Kanagawa 252-8510 Japan
3. Division of Genetics and Mutagenesis; National Institute of Health Sciences; 1-18-1, Kamiyoga, Setagaya-ku Tokyo 158-8501 Japan
4. Biological Safety Research Center; National Institute of Health Sciences; 1-18-1, Kamiyoga, Setagaya-ku Tokyo 158-8501 Japan