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

toggle caption Ben Curtis/AP

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

toggle caption ChinaFotoPress/Getty Images

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

toggle caption Lam Yik Fei/Getty Images

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

toggle caption Alex E. Proimos/via flickr

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

toggle caption Eugene Hoshiko/AP

A child is immunized against polio at the health clinic in a farming village in northern Nigeria. The procedure involves pinching two drops of the vaccine into the child's mouth. For full protection, the child needs three doses, spaced out over time. David Gilkey/NPR hide caption

toggle caption David Gilkey/NPR

Dr. Nayna Patel performs an ultrasound exam on Rinku Macwan, at a hospital near Ahmedabad, India. It's illegal in India for doctors to reveal a baby's sex during these exams, but many do it anyway. Sam Panthaky/AFP/Getty Images hide caption

toggle caption Sam Panthaky/AFP/Getty Images

A young boy plays on a commode during an event for World Toilet Day in New Delhi in November. An estimated 131 million Indian homes don't have a latrine or a clean toilet. Raveendran/AFP/Getty Images hide caption

toggle caption Raveendran/AFP/Getty Images

About a third of the world's population is thought to be infected with Mycobacterium tuberculosis, but only a small fraction of people get the disease. NIAID_Flickr hide caption

toggle caption NIAID_Flickr

If you catch dengue fever in the Western Hemisphere, it most likely came from the Aedes aegypti mosquito. Muhammad Mahdi Karim /Wikimedia.org hide caption

toggle caption Muhammad Mahdi Karim /Wikimedia.org

A Palestinian dialysis patient is treated at the Shifa hospital in Gaza City in 2010. Many kidney patients in Gaza struggle to get proper dialysis therapy because machines are often overbooked. Khalil Hamra/AP hide caption

toggle caption Khalil Hamra/AP

NPR thanks our sponsors

Become an NPR sponsor