Measles is a highly contagious respiratory disease caused by a virus. It spreads through the air through coughing and sneezing. Measles starts with a fever, runny nose, cough, red eyes, and sore throat, and is followed by a rash that spreads all over the body. About three out of 10 people who get measles will develop one or more complications including pneumonia, ear infections, or diarrhea. Complications are more common in adults and young children.