Veterinary Teaching Hospital, College of Agriculture, University of Osaka Prefecture, Sakai, Osaka 593, Japan

Department of Veterinary Clinical Pathobiology, Faculty of Agriculture, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan

Department of Veterinary Clinical Pathobiology, Faculty of Agriculture, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan

Department of Veterinary Surgery, College of Agriculture, University of Osaka Prefecture, Sakai, Osaka 593, Japan

Department of Veterinary Clinical Pathobiology, Faculty of Agriculture, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan

Department of Veterinary Clinical Pathobiology, Faculty of Agriculture, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan