Medical Specialties: Family practice, Internal medicine, Neurology

Clinical Definition

Encephalitis is a severe irritation and inflammation of the brain, usually due to infection. Most often, the infection is viral, such as the herpes simplex virus. Other causes include autoimmune disease, an allergic reaction to vaccines, bacteria and parasites, as well as the after effects of cancer.

In Our Own Words

Encephalitis, a severe and sometimes fatal inflammation of the brain, is most often caused by a virus. While meningitis affects the protective membranes covering the brain (known as the meninges), encephalitis involves the brain tissue itself. Some patients may develop both. In viral encephalitis, fever, headache, low energy and confusion are some possible symptoms. Brain scans, blood tests and a lumbar puncture are among tests to diagnose encephalitis.


If caused by infection, possible treatment includes rest, fluids and antiviral or antibiotic medication. The severity of encephalitis is variable, with some patients having a mild, short disease followed by a full recovery. Others are more severe, with permanent impairment or death. 

Relevant Conditions
Common Types
  • Viral
  • Bacterial
Side Effects
  • Fever
  • Mild headache
  • Low energy
  • Confusion
  • Stiff neck
Share this article
  • Harvard Health Publicaitons "Medical Dictionary of Health Terms." http://www.health.harvard.edu. Accessed August 2013.
  • University of Maryland Medical Center. "Encephalitis." Updated May 2013. http://umm.edu. Accessed August 2013.
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