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Encephalitis is inflammation of the brain. The inflammation may involve the whole brain or just parts of the brain. Encephalitis may just occur in individuals (sporadic) or may affect many people in a particular area (epidemic).
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Encephalitis is most often caused by a viral infection. In the United States, the most common cause of sporadic encephalitis is the herpes simplex virus (HSV). Epidemic causes of encephalitis are usually mosquito- or tick-borne viruses.
The most common viruses that cause encephalitis include:
- Viruses carried by mosquitoes such as West Nile or Eastern equine encephalitis
- Herpes simplex virus (HSV)
- Chickenpox virus
- Influenza virus
- Epstein-Barr virus (EBV)
- Polio virus
- Measles virus
- Mumps virus
Not all encephalitis is caused by a virus. Some may be due to an overreaction of the immune system.
Factors that may increase your chance of encephalitis include:
- Living, working, or playing in an area where mosquito- or tick-borne viruses are common.
Not being immunized against diseases, such as:
- A suppressed immune system caused by certain medications, or health conditions, such as HIV infection
- Having cancer—sometimes immune system overactivity may be the first sign of cancer
Newborns of mothers who have genital herpes are at risk for herpes simplex encephalitis
The symptoms may range from mild to severe. Severe symptoms can include permanent neurological damage. Encephalitis can also lead to death.
Milder symptoms include:
- Weakness, severe fatigue
- Sensitivity to light
- Stiff neck and back
- Muscle aches
More severe symptoms may include:
- Changes in consciousness
- Personality changes
- 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.
Your bodily fluids may be tested. This can be done with:
- Blood tests
- Lumbar puncture to test the cerebrospinal fluid that surrounds the brain and spinal cord
- Brain biopsy
Images may be taken of your head. This can be done with:
Your brain's electrical activity may be tested. This can be done with an electroencephalogram (EEG).
Treatment is mostly supportive. It may include:
- Antiviral drugs to shorten the duration of the illness
- Steroids to reduce brain inflammation
- Diuretics to decrease elevated intracranial pressure
- Intubation with hyperventilation to decrease elevated intracranial pressure, and to maintain respiration and ventilation
- Anticonvulsants to prevent and/or treat seizures
To help reduce your chance of encephalitis:
- Make sure that you and your children are vaccinated against preventable viral illnesses
Protect yourself from mosquito bites:
- Fix window screens.
- Drain standing water around your home.
- Wear long clothes after dark.
- Use repellent when you are 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
Herpes simplex encephalitis. EBSCO DynaMed Plus website. Available at:http://www.dynamed.com/topics/dmp~AN~T113755/Herpes-simplex-encephalitis. Updated February 14, 2015. Accessed September 23, 2016.
Eastern equine encephalitis. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T114677/Eastern-equine-encephalitis. Updated February 4, 2016. Accessed September 23, 2016.
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: http://www.ninds.nih.gov/disorders/encephalitis%5Fmeningitis/encephalitis%5Fmeningitis.htm. Updated April 16, 2014. Accessed September 23, 2014.
West Nile virus infection. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T114644/West-Nile-virus-infection. Updated July 21, 2016. Accessed September 23, 2016.
10/1/2013 DynaMed Plus Systematic Literature Surveillance http://www.dynamed.com/topics/dmp~AN~T115142/Mosquito-avoidance. 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.
- Reviewer: Rimas Lukas, MD
- Review Date: 09/2016
- Update Date: 09/23/2014