Encephalitis (en-sef-uh-LIE-tis) is inflammation of the brain. There are several causes, but the most common is a viral infection.
Encephalitis often causes only mild flu-like signs and symptoms — such as a fever or headache — or no symptoms at all. Sometimes the flu-like symptoms are more severe. Encephalitis can also cause confused thinking, seizures, or problems with movement or with senses such as sight or hearing.
In some cases, encephalitis can be life-threatening. Timely diagnosis and treatment are important because it's difficult to predict how encephalitis will affect each individual.