1. Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, Ames, Iowa, USA
2. Virus and Prion Research Unit, National Animal Disease Center, USDA, Agricultural Research Service, Ames, Iowa, USA
3. Ruminant Disease and Immunology Research Unit, National Animal Disease Center, USDA, Agricultural Research Service, Ames, Iowa, USA
4. Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA
5. Kansas State Veterinary Diagnostic Laboratory, Kansas State University, Manhattan, Kansas, USA