1. Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
2. Department of Mathematics, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
3. Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
4. National Centre for Microbiology, Instituto de Salud Carlos III (ISCIII), Epidemiology and Public Health Network of Biomedical Research Centre (CIBERESP), Madrid, Spain
5. Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA