Andrew Witty, CEO of GlaxoSmithKline, says that better control of infectious diseases in Africa is allowing chronic diseases to come to the surface. Mark Lennihan/AP hide caption

itoggle caption Mark Lennihan/AP

A boy waits to get vaccinated at an anti-polio campaign in Moradabad, India. Michaeleen Doucleff/NPR hide caption

itoggle caption Michaeleen Doucleff/NPR

Eight-year-old Manish, who caught polio years ago, learns to walk with leg braces at a rehabilitation center in New Delhi on Thursday. Manish Swarup/AP hide caption

itoggle caption Manish Swarup/AP

The fatality rate in an Ebola outbreak ranges from 25 percent to 90 percent, depending on the particular strain of the virus involved. Cynthia Goldsmith/ Centers for Disease Control and Prevention hide caption

itoggle caption Cynthia Goldsmith/ Centers for Disease Control and Prevention

Oxana and Pavel Rucsineanu fell in love while living at a tuberculosis ward in Balti, Moldova. Jason Beaubien/NPR hide caption

itoggle caption Jason Beaubien/NPR

Current water-filtering technology is costly, but MIT scientists are testing a simpler and cheaper method that uses wood from white pine trees. Wikimedia Commons hide caption

itoggle caption Wikimedia Commons

Jockeys take their camels home after racing in Egypt's El Arish desert. The annual race draws competitors from around the Middle East, including Saudi Arabia, where camels carry the Middle East Respiratory Syndrome virus. Nasser Nouri/Xinhua /Landov hide caption

itoggle caption Nasser Nouri/Xinhua /Landov

Sylvestre Mebam (right) runs an unauthorized health clinic in Cameroon's largest city of Douala. He and his assistant treat about 10 to 15 people each day. Andres Caballero/NPR hide caption

itoggle caption Andres Caballero/NPR

New research finds a close connection between the flu that devastated the horse population in North America in the 1870s and the avian flu of that period. Hulton Archive/Getty Images hide caption

itoggle caption Hulton Archive/Getty Images

Hannah Rood, 3, receives an H1N1 vaccine at a clinic in San Pablo, California, during the 2009 swine flu epidemic. Justin Sullivan/Getty Images hide caption

itoggle caption Justin Sullivan/Getty Images