Lahey Health is now part of Beth Israel Lahey Health

by Carson-DeWitt R


Encephalitis is inflammation of the brain. The inflammation may be in the whole brain or just parts of the brain. The swelling can stop the brain from working properly, increase pressure in the skull, and damage brain tissue.

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Encephalitis is often caused by a viral infection. The most common viruses that cause encephalitis include:

Not all encephalitis is caused by a virus. Some may be due to an overreaction of the immune system.

Risk Factors

Factors that may increase your chance of viral encephalitis include:

  • Living, working, or playing in an area where mosquito- or tick-borne viruses are common.
  • Not being immunized against diseases, such as:
    • Measles
    • Mumps
    • Chickenpox
    • Polio
    • Rotavirus
  • A suppressed immune system caused by certain medications, or health conditions, such as HIV infection
  • Newborns of mothers who have genital herpes are at risk for herpes simplex encephalitis.

Certain cancers can overstimulate the immune system. This can increase the risk of encephalitis.


The symptoms may range from mild to severe. Severe encephalitis can lead to permanent brain damage and death.

Milder symptoms include:

  • Fever
  • Weakness, severe fatigue
  • Headache
  • Sensitivity to light
  • Stiff neck and back
  • Vomiting
  • Muscle aches
  • Rash
  • Yawning

More severe symptoms may include:

  • Changes in consciousness
  • Personality changes
  • Confusion
  • Irritability
  • Seizures
  • Loss of mobility
  • Progressive drowsiness
  • Trouble walking
  • Trouble speaking
  • Trouble swallowing


You will be asked about your symptoms and medical history. A physical exam will be done.

To look for signs of infection your bodily fluids may be tested. This can be done with:

  • Blood tests
  • Lumbar puncture to test the fluid that surrounds the brain and spinal cord

A brain biopsy may also be done to look for problems in the brain tissue.

Images may be taken of your head to look for swelling or damage. This can be done with:

Your brain's electrical activity may be tested. This can be done with an electroencephalogram (EEG).


There are very few treatments for viruses, they simply have to run their course. Most treatment will focus on supporting the body until the virus has passed. Treatment will be based on individual needs but may include:

  • Antiviral drugs to shorten the duration of the illness
  • Steroids to reduce inflammation in the brain
  • Diuretics to decrease pressure inside the head
  • Intubation to support breathing; may also help decrease pressure in the head
  • Anticonvulsant medication to prevent and/or treat seizures


To help reduce your chance of encephalitis:

  • Make sure that you and your children have recommended vaccinations
  • Protect yourself from mosquito bites especially in area at high risk of infection. Helpful steps include:
    • Fix window screens.
    • Drain standing water around your home.
    • Wear long clothes after dark.
    • Use repellent when you are outside.
    • If you are sleeping outside, use proper mosquito netting at night. Look for netting treated with insecticide.


The Encephalitis Society 

National Institute of Neurological Disorders and Stroke 


Canadian Neurological Sciences Federation 

Health Canada 


Herpes simplex encephalitis. EBSCO DynaMed Plus website. Available at:  . Updated February 14, 2015. Accessed October 2, 2017.

Eastern equine encephalitis. EBSCO DynaMed Plus website. Available at:  . Updated February 4, 2016. Accessed October 2, 2017.

Mann AP, Grebenciucova E, Lukas RV. Anti-N-methyl-D-aspartate-receptor encephalitis: diagnosis, optimal management, and challenges. Ther Clin Risk Manag. 2014;10:517-525.

Nicholas MK, Lukas R, van Besein K. Youmans Textbook of Neurological Surgery, 6th Edition. Section II: General Neurosurgery. Chapter 46. AIDS. 2011.

NINDS meningitis and encephalitis information page. National Institute of Neurologic Disorders and Stroke website. Available at: Accessed October 2, 2017.

Serafini A, Lukas RV, VanHAerents S, et al. Paraneoplastic epilepsy. Epilepsy Behav. 2016;61:51-58.

West Nile virus infection. EBSCO DynaMed Plus website. Available at:  . Updated July 21, 2016. Accessed September 23, 2016.

10/1/2013 DynaMed Plus Systematic Literature Surveillance  . Reimer LJ, Thomsen EK, Tisch DJ, et al. Insecticidal bed nets and filariasis transmission in Papua New Guinea. N Eng J Med. 2013;369(8):745-753.

Revision Information

  • Reviewer: EBSCO Medical Review Board Rimas Lukas, MD
  • Review Date: 09/2018
  • Update Date: 03/13/2017