1. Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA
2. Departments of Veterinary Biomedical Sciences and Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 5108, USA
3. Diagnostic Virology Laboratory, National Veterinary Services Laboratories, United States Department of Agriculture, Animal and Plant Health Inspection Service, Ames, IA 50010, USA
4. Ohio Department of Health, Columbus, OH 43215, USA