Measles is a disease caused by a highly contagious virus. People with measles spread the virus through the air when they cough, sneeze, or breathe.  Symptoms of measles include high fever, cough, runny nose, red and watery eyes, and rash. Koplik spots (tiny white spots inside the mouth) can appear 2 to 3 days after symptoms begin. Some people who become sick with measles also get a serious lung infection, such as pneumonia. Although severe cases are rare, measles can cause swelling of the brain and even death. Measles can be especially severe in infants, pregnant women, and in people who have weakened immune systems.​