The Ethiopian government has set up about a dozen vaccination booths along its thousand-mile border with Somalia. Jason Beaubien/NPR hide caption

itoggle caption Jason Beaubien/NPR

Warren Buffett (left), Howard G. Buffett (center) and grandson Howard W. Buffett collaborated on a book about the challenges of feeding more than 2 billion more mouths by 2050. Scott Eells/Bloomberg/Bloomberg via Getty Images hide caption

itoggle caption Scott Eells/Bloomberg/Bloomberg via Getty Images

A young girl stands in the doorway of a home in Uttar Pradesh, India. The markings on the door show that a polio immunization team vaccinated children in the home. Alyce Henson/Courtesy of Rotary International hide caption

itoggle caption Alyce Henson/Courtesy of Rotary International

Hawah Alhassan, 5, contracted Guinea worm in a village near Tamale, Ghana, in 2007. The country eliminated the parasite in 2011. Wes Pope/MCT/Landov hide caption

itoggle caption Wes Pope/MCT/Landov

HIV-positive babies rest in an orphanage in Nairobi, Kenya. Treatment right after birth may make it possible for HIV-positive newborns to fight off the virus. Brent Stirton/Getty Images hide caption

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A nurse treats a cholera patient at the Juan Pablo Pina Hospital in San Cristobal, Dominican Republic, in August. Health officials say that the strain of cholera circulating in the country— the same one that first appeared in Haiti three years ago — has also caused outbreaks in Cuba and now Mexico. Erika Santelices/AFP/Getty Images hide caption

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Syrian opposition fighters sit on the front line in the city of Deir Ezzor on Oct. 13. Ongoing violence has ravaged the city since March 2011. AFP/Getty Images hide caption

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Clostridium difficile, a bacterium that causes severe diarrhea, can be difficult to treat with antibiotics. Stefan Hyman/University of Leicester hide caption

itoggle caption Stefan Hyman/University of Leicester

David Lozano (left) and Kevin Kreinbring stand in front of a painting created by Lozano. The couple says they get tested for HIV together every six months. Courtesy of David Lozano hide caption

itoggle caption Courtesy of David Lozano

Arunachalam Muruganantham installs his machine in a village in Chhattisgarh, India. Amit Virmani hide caption

itoggle caption Amit Virmani

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

itoggle caption Hector Retamal/AFP/Getty Images