1. Division of Pathology, National Institute of Health Sciences, 1–18–1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
2. Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan
3. Biological Safety Research Center, National Institute of Health Sciences, 1–18–1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan