1. Veterinary Epidemiology Unit, Division of Health and Environmental Sciences, School of Veterinary Medicine, Rakuno Gakuen University, 582 Bunkyodai Midorimachi, Ebetsu, Hokkaido 069–8501, Japan
2. National Center of Neurology and Psychiatry, 4–1–1 Ogawa-Higashi-cho, Kodaira, Tokyo 187–8551, Japan