Rob Knight, co-founder of the American Gut Project at the University of Colorado in Boulder, works in the lab where the samples are processed. The American Gut Project hide caption

itoggle caption The American Gut Project

Sandra Lopez (left) and her dog, Coco, greet hospice nurse Heather Meyerend last fall. In the weeks before Lopez died, Meyerend stopped by weekly to check her physical health, pain levels and medications. Amy Pearl/WNYC hide caption

itoggle caption Amy Pearl/WNYC

Dr. Mohammed Arif helps treat a wounded patient at a field hospital in Kobani, Syria. Most of the clinics in this besieged Syrian border town are now in ruins. Only one still stands, its location kept secret lest it be targeted. Jake Simkin/AP hide caption

itoggle caption Jake Simkin/AP

The dengue virus has an icosahedral shape, similar to the pattern on a soccer ball. Antibodies stop the virus by binding to its surface. Laguna Design/Science Source hide caption

itoggle caption Laguna Design/Science Source

Valerie Davidson was appointed health commissioner by Alaska's Gov. Bill Walker to help him expand Medicaid in the state. She'll look for middle ground with Republicans to get it done, she says. Lori Townsend/Alaska Public Media hide caption

itoggle caption Lori Townsend/Alaska Public Media

More than a year after he was nominated, Dr. Vivek Murthy was confirmed as the next surgeon general Monday. Back in February, Murthy testified about his nomination before a Senate panel. Charles Dharapak/AP hide caption

itoggle caption Charles Dharapak/AP

Dr. Kent Brantly speaks about the world's response to Ebola during the Overseas Security Advisory Council's Annual Briefing in Washington, D.C. last month. Alex Wong/Getty Images hide caption

itoggle caption Alex Wong/Getty Images