1. Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan, R.O.C.
2. Division of Animal Medicine, Animal Technology Institute Taiwan, Miaoli, 350, Taiwan, R.O.C.
3. Graduate Institute of Microbiology and Public Health, College of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan, R.O.C.