What is encephalitis?

Encephalitis is swelling and irritation (inflammation) of the brain. Inflammation changes the normal blood flow in the brain. This 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.

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

Most people recover if they are treated promptly. But the illness can sometimes cause long-term problems, such as trouble with speech or memory.

What causes encephalitis?

Infection with a virus is the main cause of encephalitis. The herpes simplex virus is a common cause in the United States. This is the same virus that causes cold sores and genital herpes. The viruses that cause mumps, measles, chickenpox, mono (Epstein-Barr virus), influenza, and German measles (rubella) also can cause encephalitis. But these viruses only rarely infect the brain and cause encephalitis.

Another group of viruses, called arboviruses, can spread encephalitis through bites from mosquitoes and ticks. West Nile virus is one of these viruses. But most people who are bitten by infected mosquitoes or ticks do not get any symptoms. And only a very small number of people who have symptoms get encephalitis.

Infection with the rabies virus can also lead to encephalitis, but this is very rare.

What are the symptoms?

Symptoms of encephalitis can be mild or very serious. Symptoms 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:

• Seizures.
• Tremors.
• Personality changes.
• Memory loss.
• Hallucinations (seeing or hearing things that aren't there).

Symptoms in a baby may include:

• Vomiting.
• A bulging soft spot (fontanel) on the head.
• A stiff neck and body.

Call your doctor right away if you or your child has any of these symptoms.

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.

In general, symptoms that come on suddenly and are very bad from the start point to encephalitis that can be deadly.

How is encephalitis diagnosed?

Doctors usually diagnose encephalitis by testing the fluid in the spine for increases in white blood cells and protein. A sample of spinal fluid is taken during a lumbar puncture (also known as a spinal tap). In this test, the doctor puts a needle in your lower back between the bones of the spine.

An MRI scan, which takes pictures of the inside of your body, may show bleeding, swelling, or other changes in the brain.