1. Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan 48824
2. Department of Microbiology and Molecular Genetics, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan 48824
3. Arnold School of Public Health, Department of Epidemiology and Biostatistics, University of South Carolina, Columbia, South Carolina 29208, USA