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
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
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
Colorado tick virus, which also causes Colorado tick fever
which also causes a common childhood infection with mild or vague symptoms
enteroviruses, a group of viruses that also cause
upper respiratory infections
Epstein-Barr virus, which also causes
herpes simplex viruses, a group of viruses that also cause
cold sores and
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
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:
infections with fungi, such as histoplasma and cryptococcus
infections with parasites such as those that cause
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.