Abdullah Mchumvu has been training African giant pouched rats for more than a decade in Morogoro, Tanzania. Jonathan Kalan for NPR hide caption

itoggle caption Jonathan Kalan for NPR

Doctors at a hospital in Aleppo, Syria, treat a boy injured in what the government said was a chemical weapons attack on March 19. Syria's government and rebels accused each other of firing a rocket loaded with chemical agents outside of Aleppo. George Ourfalian/Reuters/Landov hide caption

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A baby receives a polio vaccine at the Medina Maternal Child Health center in Mogadishu, Somalia, on Wednesday. Somalia has one of the lowest immunization rates in the world. Ben Curtis/AP hide caption

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A health worker collects pigeons from a trap at People's Square in Shanghai, China, earlier this month. So far, workers have tested more than 48,000 animals for the H7N9 flu virus. ChinaFotoPress/Getty Images hide caption

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A vendor weighs a live chicken at the Kowloon City Market in Hong Kong Friday. Health authorities there have stepped up the testing of live poultry from China to include a rapid test for the H7N9 bird virus. Lam Yik Fei/Getty Images hide caption

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Renande Raphael, aged 16 months, is measured to check whether she is growing normally. She's part of a trial in Haiti to see if an extra daily snack of enriched peanut butter prevents stunting and malnutrition. Alex E. Proimos/via flickr hide caption

itoggle caption Alex E. Proimos/via flickr

People sit near pigeons at a park in Shanghai Sunday. A new strain of bird flu has spread from eastern China to other provinces, with 13 deaths reported. AP hide caption

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Workers prepare an H7N9 virus detection kit at the Center for Disease Control in Beijing on April 3. AFP/Getty Images hide caption

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A child wears a mask near a closed section of a poultry market in Shanghai, where health workers detected the new bird flu, H7N9. Eugene Hoshiko/AP hide caption

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Dengue fever patients are treated in a hospital in Asuncion, Paraguay, in January. Norberto Duarte/AFP/Getty Images hide caption

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