1. Bacterial Diseases of Livestock Research Unit, National Animal Disease Center, United States Department of Agriculture, 1920 Dayton Ave, Ames, IA 50010, USA
2. Center for Veterinary Biologics, Animal and Plant Health Inspection Service, United States Department of Agriculture, Ames, IA 50010, USA
3. National Veterinary Services Laboratories, Animal and Plant Health Inspection Service, United States Department of Agriculture, Ames, IA 50010, USA