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

In rural areas of Myanmar, villagers can buy inexpensive packets of drugs, called Ya Chut, when they have malaria. But these local remedies often don't contain adequate amounts of malaria medicines. Ben de la Cruz/NPR hide caption

itoggle caption Ben de la Cruz/NPR

Dr. Aun Pyae Phyo examines a baby at the Whampa malaria clinic on the Thailand-Myanmar border. Ben de la Cruz/NPR hide caption

itoggle caption Ben de la Cruz/NPR

Average life expectancy around the world has ticked up over the past twenty years. Here it's shown for men in 2009. The extremes are in dark green and dark red, which represent 78 to 82 years old and less than 66 years old, respectively. Courtesy of the Institute for Health Metrics and Evaluation hide caption

itoggle caption Courtesy of the Institute for Health Metrics and Evaluation

Routine autopsies have become less common in the U.S. But in the past century, post-mortems helped doctors discover many new diseases. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Clostridium difficile bacteria produce a toxin that damages the intestine and causes severe diarrhea. Courtesy of David Goudling/Nature Genetics. hide caption

itoggle caption Courtesy of David Goudling/Nature Genetics.

A boy works at an illegal gold mine in northern Nigeria. Lead from these mines has sickened thousands of children in the region. David Gilkey/NPR hide caption

itoggle caption David Gilkey/NPR

A child is inoculated with the polio vaccine at a traffic checkpoint just outside Pakistan's capital, Islamabad. Roadside vaccinations help health workers reach children in mobile populations. Jackie Northam/NPR hide caption

itoggle caption Jackie Northam/NPR

United Nations Aids Executive Director Michel Sibide hugs Secretary of State Hillary Clinton after they they presented the a road map for stopping HIV around the world. Jim Watson/AFP/Getty Images hide caption

itoggle caption Jim Watson/AFP/Getty Images

An artistic model of a coronavirus infecting a cell. The family of viruses can cause mild infections, like the common cold, and severe pneumonia-like infections, such as SARS. Peter Kohama/MCT/Landov hide caption

itoggle caption Peter Kohama/MCT/Landov