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:
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 encephalitis include:
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:
More severe symptoms may include:


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:
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:


To help reduce your chance of encephalitis:


The Encephalitis Society

National Institute of Neurological Disorders and Stroke


Canadian Neurological Sciences Federation

Health Canada


Herpes simplex encephalitis. EBSCO DynaMed website. Available at: Updated February 1, 2013. Accessed September 23, 2014.

Eastern equine encephalitis. EBSCO DynaMed website. Available at: Updated June 23, 2014. Accessed September 23, 2014.

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: Updated April 16, 2014. Accessed September 23, 2014.

West Nile virus infection. EBSCO DynaMed website. Available at: Updated June 23, 2014. Accessed September 23, 2014.

10/1/2013 DynaMed 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.

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