1. Produce Safety and Microbiology Research Unit, Western Regional Research Center, United States Department of Agriculture, Agricultural Research Service, 800 Buchanan Street, Albany, California 94710, United States of America
2. Virus and Prion Research Unit, National Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, Ames, Iowa 50010, United States of America
3. CIMUS Biomedical Research Institute & Department of Medical Sciences, University of Santiago de Compostela−IDIS, 15782 Santiago de Compostela, Spain