1. Department of Veterinary Pathology, Graduate School of Agricultural and Life Sciences,The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
2. Department of Clinical Laboratory Science, Semyung University, Jecheon 390-71, Korea
3. College of Veterinary Medicine, Chungbuk National University, Cheongju 361-763, Korea