1. Department of Veterinary Science, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Izumisano, Osaka 598-8531, Japan
2. Shiga Prefectural Institute of Public Health, 13-45 Gotenhama, Otsu, Shiga 520-0834, Japan
3. Department of Mathematical Sciences, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan