1. Laboratory of Veterinary Pathology, Faculty of Veterinary Medicine, Okayama University of Science, 1-3 Ikoi-no-oka, Imabari, Ehime 794-8555, Japan
2. Japan Institute of Statistical Technology, Hibachi Building 3F, 23-3 Senjuasahi-cho, Adachi-ku, Tokyo 120-0026, Japan
3. Laboratory of Veterinary Pathology, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan