Encephalitis (Viral)

Encephalitis, or swelling of the brain, is rare. There are several causes, but infection with a virus is the most common.

Viral encephalitis may develop during or after an infection with any of several viruses, including:

Viral encephalitis can occur in otherwise healthy persons. Young children, the elderly and those with a weak immune system are most vulnerable.


Symptoms may include:

  • Sudden fever
  • Headache
  • Vomiting
  • Weakness
  • Photophobia (abnormal sensitivity to light)
  • Mental changes (such as confusion or irritability)
  • Drowsiness
  • Difficulty walking
  • Loss of balance

Severe complications can include loss of consciousness, seizures and muscle paralysis.


While some viruses can be spread from one person to another, most people will not develop encephalitis. For example, enteroviruses can be spread from person to person. However, in most people these viruses either cause no symptoms at all, or a mild respiratory or diarrhea illness.

Treatment and Prognosis

Individuals with encephalitis are usually hospitalized for treatment. The specific treatment is determined by the cause of the illness. Some viral infections are treatable with medication, and all patients are treated with supportive care until they recover. The patient's chance of recovery depends on the specific cause of the illness and the severity of the swelling in the brain and surrounding tissues and fluids.

The prognosis for viral encephalitis varies. Some cases are mild and patients recover fully. Other cases are more severe, and permanent damage or death is possible. The most severe phase of viral encephalitis may last for one to two weeks, with fever and neurologic symptoms improving gradually or suddenly. Neurologic symptoms may require many months before full recovery, and patients may require rehabilitative services.