Measles, also known as rubeola, is a highly infectious disease. It’s caused by a virus, and can be prevented by effective vaccination. The adult form is more severe than when children acquire it, and the infected adults would end up feeling way worse. Most people get better within 2 weeks. But measles can sometimes cause dangerous problems, such as lung infection (pneumonia) or brain swelling (encephalitis). In rare cases, it can even cause seizures or meningitis.