National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci said a voluntary halt to bird flu research should stay in effect. Chip Somodevilla/Getty Images hide caption

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The Ebola virus causes a deadly form of hemorrhagic fever. Frederick Murphy/CDC hide caption

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A government official in Bali, Indonesia, holds a chicken before administering an injection to cull it as a precautionary measure in April to prevent the spread of bird flu. Firdia Lisnawati/AP hide caption

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Travelers crowd around a ticketing counter at John F. Kennedy International Airport in April 2010 in New York. Jason DeCrow/AP hide caption

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A heroin user keeps a syringe tucked behind his ear at a park in the city of Medan on Indonesia's Sumatra island. Cordita-Caritas Medan, a nongovernmental organization active there, works to reduce HIV infections through rehab of drug users and a needle exchange program. Sutanta Aditya/AFP/Getty Images hide caption

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Sir Elton John speaks Monday at the 19th International AIDS Conference in Washington. Carolyn Kaster/AP hide caption

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HIV patient Darnell Hollie, 47, talks to her doctor Monica Gandhi (right) at San Francisco General Hospital. Her path from drug addict to model patient was "a lot of work, but if you want it, it's there for you," Hollie says. Richard Knox/NPR hide caption

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Drag queens at an outdoor restaurant in Copacabana incorporate safe sex messages into a show of lip-synced songs and risque jokes. Jason Beaubien/NPR hide caption

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Nurse Priscila-Grace Gonzaga with Gregg Cassin, a San Francisco gay man who has been infected with HIV since the early 1980s. He's a volunteer in a cutting-edge gene therapy experiment to see whether HIV-infected people can be given an immune system that is invulnerable to HIV infection. Richard Knox/NPR hide caption

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A lone pig roots through trash dumped over the side of a sewage canal that runs from the center of Port au Prince through Cite de Dieu. During the rainy season, the canal overflows its banks and fills nearby houses with sewage, which can carry cholera. John W. Poole /NPR hide caption

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Cambodian children and their parents sitting at Kantha Bopha Children's Hospital in Phnom Penh on July 5. Khem Sovannara/AFP/Getty Images hide caption

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