Definition

Encephalitis (pronounced in-seh-fuh-LIE-tess) is an inflammation of the brain. It may be caused by a number of different factors. One of the most common causes is direct infection of the brain by a virus or bacterium. Inflammation can also occur as a complication of some other disorder, such as mumps (see mumps entry) or herpes simplex (see herpes infections entry). About two thousand cases of encephalitis are reported in the United States each year.

Description

Inflammation of the brain is a reaction of the body's immune system. The immune system is a network of cells, tissues, and chemical substances designed to protect the body against invasion by foreign agents. Sometimes, a foreign agent gets directly into the brain. In the process of fighting off the foreign agent, brain tissues become swollen and inflamed. In other cases, the infection occurs elsewhere in the body, such as the throat...