What Is Encephalitis?

Encephalitis is an inflammation of the brain. It usually results from an infection, most often by a virus, but sometimes by bacteria, a fungus, or parasites. In rare cases, it is caused by brain injury, a drug or vaccine reaction, or poison.

A virus, or other germ in the blood stream, can be carried to the brain. Germs in the brain attract white blood cells, the body’s main line of defense against invaders, and this sets up an inflammatory reaction. The brain tissue then swells (called cerebral edema); bleeding may occur within the brain (called intracerebral hemorrhage), and brain damage may occur.

About 1 in 200,000 people develop encephalitis each year in the United States. While anyone can succumb, children, the elderly, and those with weakened immune systems are more vulnerable.

Facts About Encephalitis

  • The patients featured in the film “Awakenings” were victims of an epidemic in the 1920s of encephalitis lethargica, which left tens of thousands of people with permanent brain damage. Its cause was never definitively identified, and it was thought to have died out. However, a handful of potential new cases have cropped up in England.
  • Keeping track of encephalitis became more difficult in 1995 after it was taken off the list of illnesses that must be reported to the U.S. Centers for Disease Control and Prevention.


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