A Pakistani health worker administers the oral polio vaccine to a child during a campaign in Karachi on May 7. Because of past attacks on vaccinators, security personnel are often assigned to accompany them. Rizwan Tabassum/AFP/Getty Images hide caption
On May 13, people suspected of having the Ebola virus wait at a treatment center in the village of Bikoro, where the outbreak began in the Democratic Republic of the Congo. John Bompengo/AP hide caption
Dario Garcia, who lives in Panama, volunteers to visit people who are HIV-positive to see whether they are taking their medications. Garcia himself is HIV-positive. "I feel alone," he says. "I believe the most support I have now is from others who have been diagnosed." Jacob McCleland for NPR hide caption
Patients are treated at an Army ward in Kansas during the influenza epidemic of 1918. About 675,000 Americans died of the flu known as "la grippe." NYPL/Science Source/Getty Images hide caption
"They have forgotten us ... and many are still really suffering," says Ebola survivor Haja Bah. James Courtright for NPR hide caption
A mosquito's antenna responds to odors. Scientists are trying to figure out how the malaria parasite might trigger a change in body odor that draws in mosquitoes that carry the disease, like the Anopheles skeeter pictured above. BSIP/UIG/Getty Images hide caption
Photomicrograph of human hookworm rhabditiform larva in its early noninfectious stage, 1979. Image courtesy CDC. Smith Collection/Gado/Getty Images hide caption
The female Anopheles mosquito is a spreader of malaria. Smith Collection/Gado/Getty Images hide caption
Suspicious travel companions: Bacteria can survive for days on surfaces inside a plane. But that doesn't mean you have to take these critters home with you. Benjamin Arthur for NPR hide caption
This banner is displayed at the Institute of Lassa Fever Research and Control in Irrua Specialist Teaching Hospital in Irrua, Edo State, midwest Nigeria. Pius Utomi Ekpei/AFP/Getty Images hide caption
Blue methylene dye is used in labs to stain cells and sold in pet stores to treat tropical fish for fungal infections. It has anti-malarial properties as well. Jay Reed/NPR hide caption
By mid-January, there had been nearly 5,000 reported cases of diphtheria in the camps and 33 deaths. Allison Joyce for NPR hide caption
Researchers are working on a new way to deliver anti-HIV drugs. A six-pointed device (artist's rendering, above) folds up to fit inside a capsule. One swallowed, the capsule dissolves and the device opens up and slowly dispenses the medication. Partners Healthcare / Screenshot by NPR hide caption
Children get their diphtheria inoculation in 1944. Kurt Hutton/Getty Images hide caption