On the lookout for SARS, an employee checks a baby's temperature at the Ben Gurion Airport in Israel, in 2003. The deadly virus quickly spread around the world once it reached Hong Kong, a central travel hub. Nir Elias/Reuters/Landov hide caption

itoggle caption Nir Elias/Reuters/Landov

A health worker from Doctors Without Borders examines Ebola patient Finda Marie Kamano, 33, at her home in Conakry, Guinea, in April. The outbreak that began in February is still spreading in West Africa. Sylvain Cherkaoui/Cosmos/Courtesy of Doctors Without Borders hide caption

itoggle caption Sylvain Cherkaoui/Cosmos/Courtesy of Doctors Without Borders

Fishermen drag a net in Lake Malawi in 2012. About the size of New Jersey, the lake is home to hundreds of fish species and is considered one of the most biologically diverse lakes in the world. Ding Haitao/Xinhua/Landov hide caption

itoggle caption Ding Haitao/Xinhua/Landov

Dr. Lisa Sterman held a Truvada pill at her office in San Francisco in 2012. She prescribed Truvada to patients at high risk for HIV infection even before the Food and Drug Administration approved the medicine explicitly for that purpose. Jeff Chiu/AP hide caption

itoggle caption Jeff Chiu/AP

Contaminated water can spread diseases like cholera and typhoid. A new project aims to provide water filters in the form of an educational book. Soe Than Win/AFP/Getty Images hide caption

itoggle caption Soe Than Win/AFP/Getty Images

Muslim pilgrims wear masks to prevent infection from the Middle East respiratory syndrome in the holy city of Mecca, Saudi Arabia, on Tuesday. Hasan Jamali/AP hide caption

itoggle caption Hasan Jamali/AP

A farmworker in Riyadh, Saudi Arabia, wears a mask to protect against Middle East respiratory syndrome earlier this month. The MERS virus is common in camels. Fayez Nureldine/AFP/Getty Images hide caption

itoggle caption Fayez Nureldine/AFP/Getty Images

Even some euro bank notes may need a good scrubbing. Like dollar bills, these notes are made from cotton and they harbor an array of bacteria. Thomas Leuthard/The Preiser Project/Flickr hide caption

itoggle caption Thomas Leuthard/The Preiser Project/Flickr