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You are here : 3-RX.com > Medical Encyclopedia > Diseases and Conditions > Encephalitis
      Category : Health Centers > Brain and Nervous System


Overview, Causes, & Risk Factors | Symptoms & Signs | Diagnosis & Tests | Prevention & Expectations | Treatment & Monitoring

Encephalitis is an inflammation of the brain.

What is going on in the body?

Encephalitis is usually caused by a viral infection of the brain tissue. The infection can also be caused by bacteria, fungi, or parasites. These tiny organisms can enter the brain tissue by any of the following routes:

  • direct infection of the cells in the brain, often following a head injury
  • through the bloodstream after a bite from a tick or mosquito
  • through the respiratory or gastrointestinal tracts. They then travel through the bloodstream and invade the brain.
  • traveling up nerves to the brain. This happens with a dormant herpes infection or after a bite from an animal with rabies.
  • What are the causes and risks of the condition?

    Most cases of encephalitis are caused by a viral infection of the brain tissue. Viruses that commonly cause encephalitis include the following:

  • adenovirus, which also causes respiratory infections
  • Borrelia burgdorferi, which also causes Lyme disease
  • Colorado tick virus, which also causes Colorado tick fever
  • cytomegalovirus, which also causes a common childhood infection with mild or vague symptoms
  • enteroviruses, a group of viruses that also cause poliomyelitis and upper respiratory infections
  • Epstein-Barr virus, which also causes mononucleosis
  • herpes simplex viruses, a group of viruses that also cause cold sores and genital herpes
  • La Crosse encephalitis virus
  • measles virus, which also causes measles
  • rubella virus, which also causes German measles
  • St. Louis encephalitis virus
  • varicella zoster viruses, which also cause shingles and chickenpox
  • Western and Eastern equine encephalitis virus
  • West Nile virus
  • Bacteria that can cause encephalitis include the following:

  • leptospirosis, which also causes a flu-like illness
  • mycobacteria, a group of bacteria that also cause tuberculosis
  • mycoplasma, which also cause pneumonia
  • rickettsia, a group of bacteria that also cause Rocky Mountain spotted fever
  • West Nile virus, which also causes a flu-like illness
  • Other less-common causes of encephalitis include the following:

  • drug reactions
  • infections with fungi, such as histoplasma and cryptococcus
  • infections with parasites such as those that cause malaria
  • vasculitis, which is an inflammation of the blood vessels that supply the brain
  • People at high risk for encephalitis include those whose age is very young or very old, and those who have compromised immune systems.


    Next section


    Encephalitis: Symptoms & Signs

    Author: Danielle Zerr, MD
    Reviewer: Kathleen A. MacNaughton, RN, BSN
    Date Reviewed: 09/18/02

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