1. Department of Pathology and Immunology and Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110
2. Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104
3. Division of Microbiology and Immunology and The Center for Emerging Infectious Disease, Yerkes National Primate Research Center, Emory University School of Medicine, Atlanta, Georgia 30329