1. Department of Comparative Pathobiology, Purdue University, West Lafayette, IN 47907, USA
2. Indiana University School of Medicine, Indianapolis, IN 46202, USA
3. Department of Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA
4. Department of Veterinary Medicine, School of Veterinary Medicine, National Taiwan University, Taipei, Taiwan 10617, R. O. C.