Encephalitis, << ehn `sehf` uh LY tihs, >> is an inflammation of the brain. Many victims of encephalitis suffer only mild fever and headache for a few days. But encephalitis can cause convulsions, coma, and even death. There are many kinds of encephalitis. Most result from virus infections. Bacteria, harmful chemicals, and various tiny parasites can also cause the disease.
Symptoms of encephalitis include drowsiness, fever, headache, and muscle weakness. In addition, the disease may cause jerky movements; mental confusion; paralysis; and difficulty in hearing, seeing, speaking, and swallowing. Some victims suffer permanent brain damage, but the majority do not. Treatment depends on the nature of the specific cause of the disease.
Some viruses that cause encephalitis occur in the blood of certain kinds of animals, including birds and horses. They are transmitted to a human being by the bite of a mosquito that has previously bitten an infected animal. In some cases, viruses of such diseases as measles and mumps attack the brain and cause encephalitis. The disease can also occur as a complication of a vaccination. The symptoms of a few kinds of encephalitis appear months or even years after the infecting virus has entered the body. Such viruses are called slow viruses.
Viruses that cause encephalitis in human beings can bring about related diseases in animals. In 1971, an outbreak of Venezuelan equine encephalomyelitis, an inflammation of the brain and spinal cord, killed hundreds of horses in Texas.
Encephalitis is closely related to meningitis, an inflammation of the membranes that cover the brain and spinal cord (see Meningitis). When both the brain and the membrane covering it are inflamed, the disease is called meningoencephalitis.
See also West Nile virus.
