1. Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY 14853, USA
2. Department of Food Science, Cornell University, Ithaca, NY 14853, USA
3. North Dakota State University Veterinary Diagnostic Laboratory, ND, USA
4. Present address: Washington Animal Disease Diagnostic Laboratory, Pullman, WA 99164, USA.
5. Present address: Department of Food Science, Pennsylvania State University, State College, PA 16802, USA.