1. Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street, New Haven, CT 06511-8934, USA
2. Department of Microbiology, New York University, New York, NY, USA
3. Institute for Human Infections and Immunity and Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX, USA
4. Viral Populations and Pathogenesis Unit, Institut Pasteur, Paris, France
5. Program in Microbiology, Yale School of Medicine, New Haven, CT, USA