Encephalitis: Inflammation of the brain, which may be caused by a bacterium, a virus, or an allergic reaction. Some forms of viral encephalitis are contagious. Encephalitis usually runs a short course, with full recovery within a week, but can cause brain damage and death. Treatment of encephalitis must begin as early as possible to avoid potentially serious and lifelong effects. Depending on the cause of the inflammation, treatment may include use of antibiotics, antiviral medications, and anti-inflammatory drugs. If brain damage results from encephalitis, therapy (such as physical therapy or cognitive restoration therapy) may help patients regain lost functions.