Twins in Malawi helped scientists discover a role the gut microbiome appears to play in severe malnutrition. Photograph courtesy of Tanya Yatsunenko hide caption

itoggle caption Photograph courtesy of Tanya Yatsunenko

The British have long said, "Keep calm and carry on." But the catchphrase may need an update for health care. Keepcalm-o-matic.co.uk hide caption

itoggle caption Keepcalm-o-matic.co.uk

A boy with multiple Guinea worms sits outside a containment center in northern Ghana, February 2007. Wes Pope/Chicago Tribune/MCT /Landov hide caption

itoggle caption Wes Pope/Chicago Tribune/MCT /Landov

A copper engraving from 1656 shows a plague doctor in Rome wearing a protective suit and a mask. Artwork by Paul Furst /Wikimedia.org hide caption

itoggle caption Artwork by Paul Furst /Wikimedia.org

Microbiologist Emma Allen-Vercoe invented the Robogut, a mechanical device that mimics conditions in the human colon. Courtesy of thestar.com hide caption

itoggle caption Courtesy of thestar.com

Haitians protest against the United Nations peacekeepers in Port-au-Prince in November 2010. Hector Retamal/AFP/Getty Images hide caption

itoggle caption Hector Retamal/AFP/Getty Images

Jacqueline Syra has been living in the La Piste camp for three years. She says she has no idea when she will be able to leave. David Gilkey/NPR hide caption

itoggle caption David Gilkey/NPR

In the U.S., doctors no longer have the option of treating gonorrhea with a pill. Instead, they are advised to use an injectable antibiotic, which is still effective against the bacteria. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Infants used to be born at home to traditional midwives. Mónica Ortiz Uribe hide caption

itoggle caption Mónica Ortiz Uribe

Chiara Andolina, a malaria researcher in Thailand, feeds her mosquito colony by letting the insects bite her right arm. These mosquitoes are picky and will dine only on live human blood. Ben de la Cruz/NPR hide caption

itoggle caption Ben de la Cruz/NPR

Mosquitoes like this one can carry the virus that causes dengue fever, which may become a bigger problem in some regions as biodiversity is lost. James Gathany/CDC Public Health Image Library hide caption

itoggle caption James Gathany/CDC Public Health Image Library

The U.S. Army distributed a monthly pinup calendar to GIs, which encouraged them to protect themselves from malaria-carrying mosquitoes. Cartoon by Frank Mack for the U.S. Army./Courtesy of the Images from the History of Medicine. hide caption

itoggle caption Cartoon by Frank Mack for the U.S. Army./Courtesy of the Images from the History of Medicine.

A health official culls chickens on a poultry farm in a village on the outskirts of Katmandu, Nepal. Chickens suspected of being infected with H5N1 bird flu were found in the area in October. Prakash Mathema/AFP/Getty Images hide caption

itoggle caption Prakash Mathema/AFP/Getty Images