Pronounced: En-sef-uh-light-issEn Español (Spanish Version)
Encephalitis is swelling of the brain. The swelling 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.
Last reviewedAugust 2013by Rimas Lukas, MD; Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.