A policeman detains a suspected member of the MS-13 gang at a checkpoint in San Salvador during a ban on public transport imposed by the gangs. Encarni Pindado for NPR hide caption

itoggle caption Encarni Pindado for NPR

Black mambas are one of the fastest snakes in the world and grow up to 14 feet long. But their venom is no match for the antidote Fav-Afrique. Balint Porneczi/Bloomberg/Getty Images hide caption

itoggle caption Balint Porneczi/Bloomberg/Getty Images

A long legacy in global health: Former President Jimmy Carter has worked to end neglected diseases since 1982. Here he sits with former South African President Nelson Mandela at a ceremony in Soweto, celebrating a new AIDS project in 2002. AFP/Getty Images hide caption

itoggle caption AFP/Getty Images

A celebration erupts in the streets of the Massessehbeh village on Friday, after President Ernest Bai Koroma officially ended Sierra Leone's largest remaining Ebola quarantine. Sunday Alamba/AP hide caption

itoggle caption Sunday Alamba/AP

The PharmaChk is a bit like a litmus test for drugs: You pop in a pill at one end, and in 15 minutes, a number appears on a screen telling you the drug's potency. Mahafreen H. Mistry/NPR hide caption

itoggle caption Mahafreen H. Mistry/NPR

A woman receives the rVSV-ZEBOV Ebola vaccine at a clinical trial in Conakry, Guinea. The vaccine appears effective after only one shot. Cellou Binani/AFP/Getty Images hide caption

itoggle caption Cellou Binani/AFP/Getty Images

Slum dwellers near Calcutta get their water from a municipal pipe. Water coming out of the tap on the left is for bathing and so is untreated. The blue Zimba chlorinator is hooked up to the tap on the right, which is used for drinking water. Courtesy of Suprio Das/Zimba hide caption

itoggle caption Courtesy of Suprio Das/Zimba

A family receives treatment for cholera at a clinic run by Doctors Without Borders in Port-au-Prince, Haiti, in October 2011, a year after the overwhelming outbreak began. Ramon Espinosa/AP hide caption

itoggle caption Ramon Espinosa/AP

Russia has strict rules on dispensing painkillers. Family members say some cancer patients killed themselves because they could not obtain the medicine and the pain was too great. Andy Baker/Ikon Images/Getty Images hide caption

itoggle caption Andy Baker/Ikon Images/Getty Images

Health workers wash their hands after taking a blood sample from a child to test for the Ebola virus. On Tuesday, the workers tested people in the village outside Monrovia where a 17-year-old boy died of the disease over the weekend. Abbas Dulleh /AP hide caption

itoggle caption Abbas Dulleh /AP

The outbreak of Middle East respiratory syndrome is slowing down in South Korea, but people were still wearing surgical masks around Seoul on Monday. Ed Jones/AFP/Getty Images hide caption

itoggle caption Ed Jones/AFP/Getty Images

A police officer guards the home of a family under a 21-day Ebola quarantine in Freetown, Sierra Leone, back in March. Michael Duff/AP hide caption

itoggle caption Michael Duff/AP