Encephalitis is inflammation of the brain. Often it is caused by a viral infection, but it can be caused by bacteria. Encephalitis can cause flu-like symptoms, such as fever or severe headache, or it may go unnoticed. Most cases are mild, requiring only rest and mild pain relievers. Severe cases are rare, but if a person has a severe headache, sudden fever, drowsiness, vomiting, confusion or seizures, immediate treatment may be necessary. Infants also can have encephalitis, which can cause excessive crying, body stiffness, and bulging in the soft spots of the skull.