Encephalitis is inflammation of the brain. The inflammation may involve the whole brain, or just parts of the brain.


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Viral infection of the central nervous system can be asymptomatic, present with mild symptoms, or cause meningitis]]> and/or encephalitis. Most cases of encephalitis are caused by a viral infection. Encephalitis may be sporadic or epidemic. In the United States, the most common cause of sporadic encephalitis is the ]]>herpes simplex virus]]> . Epidemic encephalitis are usually ]]>mosquito]]> - or tick-borne, which may be dependant on the geography and season.

The most common viruses that cause encephalitis include:


Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. Risk factors for encephalitis include:

  • Living, working, or playing in an area where mosquito-borne viruses are common
  • Not being immunized against diseases such as:
    • Measles
    • Mumps
    • Chickenpox
    • Polio
  • Having cancer]]>
  • Taking immunosuppressive medications after organ transplant
  • Having ]]>AIDS]]>

Newborns of mothers who have ]]>genital herpes simplex]]> are at risk for herpes simplex encephalitis.



The symptoms may range from mild, such as fever and headache, to severe, such as seizures]]> , loss of consciousness, and permanent neurological damage. Death may also result.

Symptoms include:

  • Fever
  • Weakness, severe fatigue
  • Headache
  • Sensitivity to light
  • Stiff neck and back
  • Vomiting
  • Changes in consciousness
  • Muscle aches
  • Rash
  • Personality changes
  • Confusion
  • Irritability
  • Seizures
  • Partial or complete ]]>paralysis]]>
  • Progressive drowsiness
  • Yawning
  • Trouble walking
  • Trouble speaking
  • Trouble swallowing



The doctor will ask about your symptoms and medical history, and perform a physical exam.

Tests may include:

  • Blood tests—to look for signs of infection
  • Spinal tap]]> —to test spinal fluid for signs of infection
  • ]]>CT]]> and/or ]]>MRI]]> scans of the head—to look for abnormal areas of enhancement, hemorrhage, or edema in the brain
  • ]]>Electroencephalogram]]> (EEG)— to look for abnormal electrical activity in the brain
  • Brain ]]>biopsy]]> —removal of a small sample of brain tissue to test for signs of infection


Treatment is mostly supportive. It may include:

  • Antiviral drugs (eg, intravenous acyclovir for herpes simplex encephalitis)—to potentially help shorten the duration of the illness
  • Steroid medications—to decrease brain swelling
  • Diuretics such as mannitol—to decrease elevated intracranial pressure
  • Intubation with hyperventilation—to decrease elevated intracranial pressure
  • Anticonvulsant medications—to prevent and/or treat seizures


Make sure that you and your children are vaccinated against preventable viral illnesses.