1. Department of Infectious Diseases, University of Georgia, Georgia, USA
2. Work was performed at the Tifton Veterinary Diagnostic and Investigational Laboratory, University of Georgia, Tifton, Georgia, USA
3. Animal Disease Diagnostic Laboratory and Department of Comparative Pathobiology, Purdue University, Indiana, USA
4. Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, New Bolton Center, Pennsylvania, USA