Researchers at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., use eggs to see if the Asian strain of the H5N1 bird flu virus has entered the U.S. in this photo from 2006. Andy Manis/AP hide caption

itoggle caption Andy Manis/AP

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

Rukhsana Bibi (center) mourns for her daughter, polio worker Madiha Bibi, killed by unknown gunmen, at a local hospital in Karachi on Tuesday. Gunmen staged additional attacks Wednesday. Fareed Khan/AP hide caption

itoggle caption Fareed Khan/AP

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

Massachusetts Gov. Deval Patrick says uncertainty about a federal budget deal in Washington played a big part in his recent announcement of cuts to his state's budget by $500 million. Steven Senne/AP hide caption

itoggle caption Steven Senne/AP

An employee tidies boxes of medicines displayed in a pharmacy in the city of Caen in western France last month. Beginning in 2013, girls between the ages of 15 and 18 will be able to get birth control free of charge, and without parental notification. Charly Triballeau/AFP/Getty Images hide caption

itoggle caption Charly Triballeau/AFP/Getty Images

A prefectural officer carries a chicken on a poultry farm on Oct. 15 on the outskirts of Kathmandu, Nepal, where chickens suspected of being infected with bird flu were found. Prakash Mathema /AFP/Getty Images hide caption

itoggle caption Prakash Mathema /AFP/Getty Images

A boy in Lima, Peru, receives a hepatitis B vaccine during an immunization drive in 2008. The United Nations is considering a ban on the preservative thimerosal, which is often used in hepatitis B and other vaccines in developing countries. Martin Mejia/AP hide caption

itoggle caption Martin Mejia/AP

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