Shops are closed in Monrovia's West Point neighborhood as part of a quarantine to contain the spread of Ebola. Zoom Dosso/AFP/Getty Images hide caption

itoggle caption Zoom Dosso/AFP/Getty Images

Ebola virus survivor Dr. Kent Brantly (center) and his wife, Amber (left), walk at a news conference at Emory University Hospital in Atlanta Thursday. Brantly and aid worker Nancy Writebol were discharged from the hospital less than a month after they contracted Ebola while treating patients in Liberia. Erik S. Lesser/EPA/LANDOV hide caption

itoggle caption Erik S. Lesser/EPA/LANDOV

Police officers guard an entrance to Emory University Hospital after an ambulance arrived transporting an American that was infected with the Ebola virus on Saturday. A specially outfitted plane carrying Dr. Kent Brantly from West Africa transpoted him to a military base in Georgia. Another American with Ebola is expected to join him at the hospital in a few days. David Goldman/AP hide caption

itoggle caption David Goldman/AP

In 1995, amid an Ebola outbreak, Zairian Red Cross personnel picked up sick people and bodies left on the streets of Kikwit, 250 miles from the capital Kinshasa. Jean-Marc Bouju/AP hide caption

itoggle caption Jean-Marc Bouju/AP

Red Cross volunteers prepare to bury the body of an Ebola victim in Pendembu, Sierra Leone, early this month. Tommy Trenchard for NPR hide caption

itoggle caption Tommy Trenchard for NPR

The CDC's director, Tom Frieden, testified before a congressional subcommittee Wednesday regarding a recent anthrax incident and lab safety improvements he is instituting. AFP/Getty Images hide caption

itoggle caption AFP/Getty Images

Particles of H5N1 virus — a particularly dangerous type of bird flu that can infect people — attack lung cells. Chris Bjornberg/Science Source hide caption

itoggle caption Chris Bjornberg/Science Source

Sick with chikungunya, Karla Sepulveda, 5, waits in a public hospital with her grandmother in Boca Chica, Dominican Republic, on May 15. The Caribbean nation has reported more than 100,000 cases this year. Ezequiel Abiu Lopez/AP hide caption

itoggle caption Ezequiel Abiu Lopez/AP

Deaths from oxycodone overdoses fell sharply in Florida after the state cracked down on pain clinics and implemented dispensing restrictions. Robin Nelson/Zumapress/Corbis hide caption

itoggle caption Robin Nelson/Zumapress/Corbis

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

John Hartigan, proprietor of Vapeology LA, a store selling electronic cigarettes and related items, takes a puff from an electronic cigarette in Los Angeles. Reed Saxon/AP hide caption

itoggle caption Reed Saxon/AP

The Centers for Disease Control and Prevention's PulseNet service monitors clusters of sickness linked to potentially dangerous strains of foodborne pathogens such as E.coli or salmonella. Reed Saxon/AP hide caption

itoggle caption Reed Saxon/AP

The Eagle Mountain Church in Newark, Texas, was linked to at least 21 cases of measles this year, mostly in children. LM Otero/AP hide caption

itoggle caption LM Otero/AP