Maria Carmen Castro, 46, of Lima, Peru, is a survivor of MDR-TB — multidrug-resistant tuberculosis. Partners In Health treated her and loaned her money to open a small store. "Because of my TB and thanks to God and Partners In Health, now I have my own business," she says. Jason Beaubien/NPR hide caption

itoggle caption Jason Beaubien/NPR

Grey lines connecting health care workers (marked with "+") and patients represent contacts between them. The red figures are carriers of MRSA. Obadia et al./PLOS Computational Biology hide caption

itoggle caption Obadia et al./PLOS Computational Biology

The effects of malaria in the brain are clear: A healthy brain, right, has many grooves and crevices. But when the brain swells up, left, these crevices smooth out. Courtesy of Michigan State University hide caption

itoggle caption Courtesy of Michigan State University

The rapid Ebola test from Corgenix Medical Corporation is small and easy to use. But because it involves blood, health workers would still need to run the test at a lab to stay safe. Courtesy of Corgenix Medical Corp. hide caption

itoggle caption Courtesy of Corgenix Medical Corp.

One form of carbapenem-resistant bacteria seen in culture. CRE bacteria are blamed for 600 deaths a year in the U.S. and can withstand treatment by virtually every kind of antibiotic. CDC hide caption

itoggle caption CDC

Measles is highly contagious, and it produces fever and rash in susceptible people who become infected. Hazel Appleton/Health Protection Agency Centre/Science Source hide caption

itoggle caption Hazel Appleton/Health Protection Agency Centre/Science Source

Dr. Kwan Kew Lai volunteered for six weeks at an Ebola treatment center run by International Medical Corps in Bong, Liberia. Courtesy of Kwan Kew Lai hide caption

itoggle caption Courtesy of Kwan Kew Lai

The Pseudomonas stutzeri bacterium, commonly found in soil, was the most prevalent subway microbe. Lower Manhattan was its prime hangout. Mason/Cell Systems 2015 hide caption

itoggle caption Mason/Cell Systems 2015

Leah Russin, of Palo Alto, Calif., holds her son, Leo, 16 months, as she speaks Wednesday at a news conference in support of proposed state legislation that would require parents to vaccinate all school children. Rich Pedroncelli/AP hide caption

itoggle caption Rich Pedroncelli/AP

Jackie Carnegie immunizes Mabel Haywood in a Colorado Health Department immunization van in 1972. Shots for measles and other infectious diseases were offered. Ira Gay Sealy/Denver Post Archive/Getty Images hide caption

itoggle caption Ira Gay Sealy/Denver Post Archive/Getty Images

Writer Roald Dahl and his wife, actress Patricia Neal, with two of their children, Theo and Chantel Sophia "Tessa." The photo was taken a few years after oldest daughter, Olivia, died of measles. Hulton Archive/Getty Images hide caption

itoggle caption Hulton Archive/Getty Images

Biologist Rob Knight, co-founder of the American Gut Project, recently moved the project to the University of California, San Diego's School of Medicine. Casey A. Cass/University of Colorado hide caption

itoggle caption Casey A. Cass/University of Colorado