Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, MO, USA. Key Laboratory of Marine Drugs, Ministry of Education, Ocean University of China, Qingdao, China. Department of Medicine, Division of Infectious Diseases, Washington University School of Medicine, St. Louis, MO, USA. Program in Virology, Harvard Medical School, 200 Longwood Ave, Boston, MA, USA. Department of Medicine, Division of Gastroenterology, Washington School of Medicine, St. Louis, MO, USA. Department of Pathology, Stanford School of Medicine, Stanford, CA, USA. VA Palo Alto Health Care System, Department of Veterans Affairs, Palo Alto, CA, USA. Department of Medicine, Division of Gastroenterology and Hepatology, and Department of Microbiology and Immunology, Stanford School of Medicine, Stanford, CA, USA. Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO, USA.