1. Department of Veterinary Public Health, School of Veterinary Medicine; Rakuno Gakuen University; Ebetsu Hokkaido 069 Japan
2. Department of Veterinary Pathology, School of Veterinary Medicine; Rakuno Gakuen University; Ebetsu Hokkaido 069 Japan
3. Department of Food Hygiene & Nutrition; Tokyo Metropolitan Research Laboratory of Public Health; Shinjuku-ku Tokyo 160 Japan