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