1. Department of Bioscience Technology, Chung Yuan Christian University, 200 Chung Pei Road, Chung Li 32023, Taiwan, ROC
2. School of Veterinary Medicine, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, ROC
3. Department of Comparative Pathobiology, Purdue University, 406 South University Street, West Lafayette, Indiana 47907, USA