Each year thousands of people from around the world tour the Gomantong Cave in Borneo. Although scientists have found a potentially dangerous virus in bats that roost in the cave, no one has ever gotten sick from a trip here. Razis Nasri hide caption
Once called the "Dutchmen" because of their large noses and large bellies, proboscis monkeys live only in Borneo. Ecosystems that have a lot of diverse animals, like this monkey, also tend to have a lot of diverse viruses. Charles Ryan hide caption
From left: A scene from the video of a car crash test; illustration of a mosquito transmitting the Zika virus; a menstrual shed in Nepal. Insurance Institute for Highway Safety/YouTube; BSIP/UIG via Getty Images; Poulomi Basu/Magnum Emergency Fund hide caption
Dr. Raj Panjabi has his blood pressure checked by a Liberian community health worker. Courtesy of Last Mile Health hide caption
A patient is pictured at a camp for diarrhea patients in Dhaka, Bangladesh. Among the past nominations for untold story: the need for vaccines to prevent "severe, deadly diarrhea" in this part of the world. Zakir Hossain Chowdhury/Barcroft Media via Getty Images hide caption
A trio of toilets, photographed by Samantha Russell, a Peace Corps volunteer, in Viti Levu Island, Fiji. Samantha Russell/Courtesy of PATH hide caption
A young woman is tested for HIV at a health clinic in Uganda. During the presidency of George W. Bush, the U.S. substantially ramped up spending on HIV/AIDS programs abroad — a commitment that retains strong bipartisan support to this day. Per-Anders Pettersson/Getty Images hide caption
Sudanese dockers unload a U.S. aid shipment at Port Sudan on the Red Sea coast on May 5. Ashraf Shazly/AFP/Getty Images hide caption
An image of the Ebola virus taken by an electron microscope. Scott Camazine/Getty Images/Science Source hide caption
Robert Langdon (Tom Hanks) and Sienna Brooks (Felicity Jones) try to evade a drone in Boboli Gardens in Inferno. Jonathan Prime/Sony PIctures hide caption
Men protesting in support of more money for AIDS research marched down Fifth Avenue during the 14th annual Lesbian and Gay Pride parade in New York in 1983. Mario Suriani/AP hide caption