Vampire bats are common in Central and South America, where they feed on livestock and sometimes people. Michael & Patricia Fogden/Corbis hide caption

itoggle caption Michael & Patricia Fogden/Corbis

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

itoggle caption Chip Somodevilla/Getty Images

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

itoggle caption Frederick Murphy/CDC

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

itoggle caption Firdia Lisnawati/AP

"You've been condomized!" said Joy Lynn Alegarbes, of The Condom Project, which promoted safe sex at the 19th International AIDS Conference. The group handed out more than 850,000 condoms this week. Benjamin Morris/NPR hide caption

itoggle caption Benjamin Morris/NPR

Dr. Lisa Sterman holds Truvada pills at her office in San Francisco. The drug was recently approved by the Food and Drug Administration to prevent infection in people at high risk of infection with HIV. The pill, already used to treat people with HIV, also helps reduce the odds they will spread the virus. Jeff Chiu/AP hide caption

itoggle caption Jeff Chiu/AP

A mobile clinic set up to test students for HIV is parked near Madwaleni High School in Mtubatuba, KwaZulu-Natal, South Africa on March 8, 2011. Parts of the South African province have HIV rates that are more than twice the national average. Stephane de Sakutin/AFP/Getty Images hide caption

itoggle caption Stephane de Sakutin/AFP/Getty Images

Activist Alexandra Volgina (right) accepts the Red Ribbon Award at the 19th International AIDS Conference for her grassroots group Patients in Control, which has worked to improve HIV treatment programs in Russia. Ryan Rayburn/IAS hide caption

itoggle caption Ryan Rayburn/IAS

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

itoggle caption Jason DeCrow/AP

Health care workers in South Africa speak to residents during a door-to-door AIDS awareness campaign, part of a series of prevention efforts that has helped lower the country's HIV infection rate. Mujahid Safodien /Reuters /Landov hide caption

itoggle caption Mujahid Safodien /Reuters /Landov

Elton John speaks at the International Aids Conference in Washington, D.C., on Monday. Carolyn Kaster/AP hide caption

itoggle caption Carolyn Kaster/AP