1. Veterinary Medical Research Institute, Iowa State University, Ames, IA 50011–1240
2. Veterinary Diagnostic Laboratory, Iowa State University, Ames, IA 50011–1240
3. Veterinary Diagnostic Medicine, College of Veterinary Medicine, University of Minnesota, St. Paul, MN 5510 8
4. Animal Disease Research and Diagnostic Laboratory, South Dakota State University, Brookings, SD 57007–1396