At least nine people aged from 8 months to 21 years have contracted measles while visiting Disneyland and Disney California Adventure in California.
It is believed that a person with infectious measles was at one of the theme parks and spread the disease. The Centers for Disease Control and Prevention says the best prevention is vaccination.
"Measles starts with a fever. Soon after, it causes a cough, runny nose, and red eyes. Then a rash of tiny, red spots breaks out. Measles can be serious for young children. It can lead to pneumonia, encephalitis (swelling of the brain), and death," the CDC explained.