1. Bacterial Diseases of Livestock, National Animal Disease Center, USDA, Ames, IA 50010, USA
2. Agri-Food and Biosciences Institute, Virology Branch, Veterinary Sciences Division, Belfast BT4 3SD, UK
3. Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA