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Brain & Nervous System Health Center

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Encephalitis - Topic Overview

What is encephalitis?

Encephalitis is inflammation of the brain. This inflammation can cause symptoms such as confusion, a fever, a bad headache, and a stiff neck. Sometimes it leads to symptoms like seizures and personality changes. It can also cause long-term problems, such as trouble with speech or memory.

Encephalitis is uncommon, but it can be deadly. If you think you have symptoms of encephalitis, see a doctor right away.

What causes encephalitis?

Infection with a virus is the main cause of encephalitis. Different types of viruses can cause the illness. For example, West Nile virus can cause encephalitis when a person is bitten by an infected mosquito. Another type is the herpes simplex virus, which is the same virus that causes cold sores and genital herpes. A mother who is infected with the herpes virus can also pass the virus to her baby. If this happens and the baby gets encephalitis, it is very serious.

Encephalitis also can be caused by bacteria or by a parasite, such as the one that causes toxoplasmosis. In rare cases, encephalitis can be caused by a fungus.

But most people who get these types of infections don't get encephalitis.

What are the symptoms?

Symptoms of encephalitis can include:

  • Confusion.
  • A fever.
  • A headache (which can be very painful).
  • A stiff neck and back.
  • Light hurting your eyes.
  • Nausea and vomiting.
  • Lack of energy.
  • Drowsiness.

More serious symptoms include:

If you think that you or your child has encephalitis, call your doctor right away.

Early on, symptoms of encephalitis may be like those of meningitis. This is a serious viral or bacterial illness that causes swelling of the tissues around the brain and spinal cord.

How is encephalitis diagnosed?

Your doctor will ask questions about your past health and your symptoms. He or she will likely order tests to confirm the diagnosis. These may include:

  • Spinal fluid analysis. By doing a lumbar puncture (also called a spinal tap), your doctor can check the spinal fluid for an increase in white blood cells and protein. The bacteria, virus, parasite, or fungus causing the encephalitis also may be found in the spinal fluid.
  • Imaging tests. An MRI or CT scan, which takes pictures of the inside of your body, may show bleeding, swelling, or other changes in the brain. See a picture of a brain with encephalitis camera.gif.
  • Electroencephalogram (EEG). This test can measure the electrical signals in the brain. It may show a change related to the illness.
  • Blood tests. These tests can show what type of virus is causing encephalitis.
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