1. Departments of Veterinary Diagnostic Medicine, University of Minnesota, 1333 Gortner Avenue, St. Paul, MN 55108
2. The Clinical and Population Sciences, University of Minnesota, 1333 Gortner Avenue, St. Paul, MN 55108
3. College of Veterinary Medicine, University of Minnesota, 1333 Gortner Avenue, St. Paul, MN 55108, the Respiratory Disease of Livestock Research Unit, National Animal Disease Center, United States Department of Agriculture, Agricultural Research Service, Ames, IA 50010
4. The Diagnostic Virology Laboratory, National Veterinary Services Laboratories, Ames, IA 50010.