Illustration Credits:

1 (b) iStockphoto; 2 © PhotoDisc; 4 (b) © Digital Stock; 5 (l) iStockphoto; (r) Cynthia Goldsmith/CDC; 6 © Dennis Kunkel Microscopy, Inc.; 7 (t) iStockphoto; (b) © PhotoDisc; 8 (both) James Gathany/CDC; 9 artwork based on drawings by Kathryn Born; 10 Getty Images; 12 (l) © Corbis; (r) iStockphoto; 13 (l) iStockphoto; (r) © 2010 Star Tribune/Minneapolis-St.Paul; 14 (t) iStockphoto; (b) Janice Haney Carr/CDC; 15 (t) iStockphoto; (b) AFP/Getty Images; 16 Getty Images; 17 Cynthia Goldsmith/CDC; 18 iStockphoto; 19 André Roussel, USAID/Benin; 20 C. S. Goldsmith and A. Balish/CDC; 21 (l) Office of the Public Health Service Historian; (r) James Gathany/CDC; 22–23 iStockphoto; 24 (t) © PhotoDisc; (b) Janice Haney/CDC; 25 iStockphoto; 28 (t) Reprinted with permission from L. Hufnagel, D. Brockmann, and T. Geisel. 2004. Forecast and control of epidemics in a globalized world. Proceedings of the National Academy of Sciences 101(42):15124–15129. © 2004 National Academy of Sciences, U.S.A.; (b) iStockphoto; 29–30 iStockphoto; 31 USAID; 32 (l) Laura Rose/CDC; (r) www.fbi.gov; 35 Getty Images; 36 iStockphoto; 37 James Gathany/CDC; 38 Keith Weller/USDA; 39 iStockphoto; 40 WHO, Christopher Black; 41 NASA.

The cover is a digitally colorized, negative-stained transmission electron micrograph depicting several influenza A virus particles. Credit: F. A. Murphy/CDC.