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Encephalitis is an inflammation (swelling) of the brain. Encephalitis is usually caused by a virus, but other things (including bacteria) can also cause it.

What Is Encephalitis?

Encephalitis (pronounced: in-seh-fuh-LYE-tus) is typically caused by three different groups of viruses:

  1. The herpes viruses, which includes chickenpox, EBV (Epstein-Barr virus, the virus that causes mono), and herpes simplex (the virus that causes cold sores).
  2. Viruses and other germs that are transmitted by insects, like West Nile virus (transmitted through a mosquito bite) and the germs that cause Lyme disease and Rocky Mountain spotted fever (transmitted through tick bites).
  3. Viruses that cause childhood infections that used to be common, such as measles, mumps, and German measles. But because many countries immunize against them, it’s rare today for someone to develop encephalitis as a result of these illnesses.

Some cases of encephalitis are mild and symptoms only last for a short time. However, it is possible to develop a severe case of encephalitis that can be serious and possibly even life threatening. When a person has encephalitis, his or her brain becomes inflamed (inflammation means swelling and irritation).

Is It Contagious?

Infection with many different viruses can lead to encephalitis. So how contagious the infection is depends on which virus caused it. Viruses like West Nile are only transmitted through the bite of infected insects; it’s not possible to catch them from other people. But viruses like EBV are passed from person to person.

Even if someone catches a virus that can cause encephalitis, that does not mean that person will automatically develop the condition. In fact, very few people who are infected with these viruses actually develop encephalitis.

Signs and Symptoms

Encephalitis may cause fever, headache, poor appetite, loss of energy, or just a general sick feeling. In more severe cases, other symptoms might occur, including:

  • high fever
  • severe headache
  • sensitivity to light (called photophobia, which means light hurts your eyes)
  • nausea and vomiting
  • stiff neck
  • confusion
  • sleepiness, difficulty waking, or unconsciousness
  • convulsions (seizures)

When encephalitis happens after a common illness like chickenpox, the signs and symptoms of that illness usually come before symptoms of inflammation in the brain. But encephalitis can also appear without warning. If you have symptoms of encephalitis, get in touch with your doctor right away.

Diagnosis and Treatment

To diagnose encephalitis, the doctor may take blood samples and perform a spinal tap (also called a lumbar puncture), a procedure that involves inserting a very thin needle into the lower back to remove some cerebrospinal fluid (CSF) that surrounds the brain and spinal cord. The samples will be sent to a laboratory to be checked for viruses or bacteria.

A brain scan (an MRI or a CT scan) might be done to look for inflammation, and the doctor also might order an electroencephalogram (EEG), a test that records brain waves and can reveal any abnormalities consistent with encephalitis.

Treatment for encephalitis depends on the virus or other germ that caused it. Teens with mild cases of encephalitis can recover at home as long as they’re watched carefully by a parent or other adult in the household. Most cases of encephalitis just run their course and the person gets better without treatment.

Some viruses that cause encephalitis can be treated with medication. For example, acyclovir, an antiviral drug, can help treat encephalitis caused by the herpes simplex virus. In addition, steroid medications can be used to reduce swelling in the brain (these aren’t the same as the dangerous performance-enhancing steroids that some athletes use). Because antibiotics are not effective against viruses, they’re not used to treat viral encephalitis.

Severe cases of encephalitis require a hospital stay so the patient can be carefully monitored and medical treatment is close at hand if needed. For people who have had severe encephalitis that has affected some of the brain’s functions, doctors may recommend physical therapy or speech therapy to help with recovery.

How Long Does It Last?

The worst symptoms of encephalitis generally last up to 1 week, but full recovery may take weeks or longer. Because encephalitis affects the brain, people with severe cases can sometimes develop problems like seizures, difficulties with muscle coordination, and learning disabilities.

Can I Prevent Encephalitis?

The best way to prevent encephalitis is to avoid getting infected with the viruses or other germs that can cause it. Regular hand washing will help limit the spread of some of these germs. Staying as healthy as possible by eating a balanced diet and getting plenty of rest can help keep your immune system in shape. Immunizations are also an important way to protect people from diseases like chickenpox and measles.

In areas where viruses and other germs are transmitted by insect bites, protect yourself by wearing long sleeves and pants and applying an insect repellent. Also, try to avoid unnecessary outdoor activities at dawn and dusk when mosquitoes are most likely to bite.

Reviewed by: Nicole A. Green, MD
Date reviewed: April 2013