©2008 WGBH Educational Foundation. All Rights Reserved. Animation adapted from Viral Fusion ©2008 University of Massachusetts and XVIVO Scientific Animation. Production by Irene Bosch, Michael Astrachan, and David Bolisnky. Animation by Janet Iwasa, Gaël McGill, Digizyme Inc. Composting, editing, and art direction by Michael Astrachan, XVIVO. Narrative and data from Yorgo Modis, Yale University. Music production by Alonsound. Acknowledgements: University of Massachusetts Medical School, Emory University School of Medicine, Stanford University School of Medicine, Dana-Farber Cancer Institute, Mount Sinai School of Medicine, Oklahoma Medical Research Foundation, Immunology and Cancer Program, Baylor Institute for Immunology Research, Cooperative Centers for Translational Research on Human Immunology and Biodefense U19-AI057319, National Institute of Allergy and Infectious Diseases, National Institutes of Health, US. Additional images courtesy of US Department of Agriculture and Center for Disease Control and Prevention: James Gathany (photographer), Frank Hadley Collins and Paul I. Howell (content providers).