Nurse Irena Majola tests Justice Mlambo's blood for HIV at a roadside AIDS testing table in a suburb near Cape Town. Under the "test and treat" strategy, about 45 million South Africans would need to be screened for HIV each year. Rodger Bosch/AFP/Getty Images hide caption

itoggle caption Rodger Bosch/AFP/Getty Images

A cross-sectional X-ray shows what's called a "sunken chest." The bright circle near the bottom is the spine; the gray blob on the right is the heart. Living LLC/Getty Images hide caption

itoggle caption Living LLC/Getty Images

Ruben Bermudez stands in front of a sign that says in Spanish, "To love yourself is to protect yourself." He has struggled to remain eligible for AIDS drug assistance programs since he went on treatment four years ago. Jessica Camille Aguirre/NPR hide caption

itoggle caption Jessica Camille Aguirre/NPR

A PET scan of the brain of a person with Alzheimer's disease. U.S. National Institute on Aging/via Wikimedia Commons hide caption

itoggle caption U.S. National Institute on Aging/via Wikimedia Commons

Brian Lawson rolls a marijuana cigarette at the BC Marijuana Party Headquarters in Vancouver, British Columbia. Vancouver is in the marijuana-friendly corner of Canada. Jae C. Hong/AP hide caption

itoggle caption Jae C. Hong/AP