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What Is Encephalitis?

Encephalitis is an inflammation (swelling and irritation) of the brain. In most cases, a virus causes this inflammation.

Encephalitis is also called acute viral encephalitis or aseptic encephalitis.

Who Gets Encephalitis?

Encephalitis (in-seh-fuh-LYE-tus) is a rare disease. Most cases happen in children, the elderly, and people with a weakened immune system (from HIV/AIDS, cancer, etc.).

Several thousand cases of encephalitis are reported to the Centers for Disease Control and Prevention (CDC) every year. But health experts think that many more cases happen that aren't reported because symptoms vary and can be mild.

What Are the Signs & Symptoms of Encephalitis?

Symptoms in mild cases of encephalitis usually include:

  • fever
  • headache
  • poor appetite
  • loss of energy
  • a general sick feeling

Serious cases of encephalitis can cause:

  • a high fever
  • severe headache
  • nausea and vomiting
  • stiff neck
  • confusion
  • personality changes
  • convulsions (seizures)
  • problems with speech or hearing
  • hallucinations
  • memory loss
  • drowsiness
  • coma

It's harder to spot some of these symptoms in infants. Important signs to look for include:

  • vomiting
  • a full or bulging soft spot (fontanel)
  • crying that doesn't stop or that seems worse when the baby is picked up or handled
  • body stiffness
  • lethargy (not being very active)

Because encephalitis can happen during or after common viral illnesses, symptoms of these illnesses can start before encephalitis happens. But often, it appears without warning.

What Causes Encephalitis?

Three groups of viruses are common causes of encephalitis:

  1. Herpes viruses, such as chickenpox, EBV (Epstein-Barr virus, which causes mono), and herpes simplex (which causes cold sores).
  2. Viruses and other germs transmitted by insects, like West Nile virus (spread through a mosquito bite) and the germs that cause Lyme disease and Rocky Mountain spotted fever (spread through tick bites).
  3. Viruses that cause once-common childhood infections, such as measles, mumps, and German measles. Thanks to vaccines, it's rare today for someone to develop encephalitis from these illnesses.

Less often, encephalitis can be:

  • caused by an infection from bacteria , such as bacterial meningitis
  • a complication of other infectious diseases like syphilis
  • due to a parasite, like toxoplasmosis (found in infected cat feces) in people with weak immune systems

In many cases, the cause of encephalitis isn't known.

Is Encephalitis Contagious?

Brain inflammation itself is not contagious. But the viruses that cause encephalitis can be. Of course, getting a virus does not mean that someone will develop encephalitis.

How Is Encephalitis Diagnosed?

Doctors use several tests to diagnose encephalitis, including:

  • imaging tests, such as computed tomography (CT) scans or magnetic resonance imaging (MRI), to check the brain for swelling, bleeding, or other problems
  • electroencephalogram (EEG), which records the electrical signals in the brain, to check for unusual brain waves
  • blood tests to look for bacteria or viruses in the blood. These also can show if the body is making antibodies (specific proteins that fight infection) in response to a germ
  • lumbar puncture, or spinal tap, which checks cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) for signs of infection

How Is Encephalitis Treated?

Most kids with encephalitis need care in a hospital, usually in an intensive care unit (ICU). Doctors will watch their blood pressure, heart rate, breathing, and body fluids to prevent further swelling of the brain.


  • Antiviral drugs can treat some forms of encephalitis, such as the type caused by the herpes simplex virus.
  • Corticosteroids may be used to reduce brain swelling.
  • Anticonvulsants might be given to a child having seizures.
  • Medicines you can buy without a prescription, like acetaminophen, can help with fever and headaches.
  • Antibiotics don't work against viruses, so aren't used to treat most forms of encephalitis.

Many people with encephalitis make a full recovery. In some cases, brain swelling can cause lasting problem like learning disabilities, speech problems, memory loss, hearing loss, or lack of muscle control. Speech therapy, physical therapy, or occupational therapy can help in these cases.

How Long Does Encephalitis Last?

Most of the time, the acute phase of the illness (when symptoms are the most severe) lasts up to a week. Full recovery can take longer, often several weeks or months.

Can Encephalitis Be Prevented?

Encephalitis can't be prevented, but you can avoid the illnesses that may lead to it. Vaccines protect kids from many common childhood illnesses. So follow the schedule recommended by your doctor. Kids should also avoid contact with anyone who already has encephalitis.

It's also important for everyone in your family to wash their hands well and often.

To avoid mosquito bites, kids should:

  • Avoid being outside at dawn and dusk when mosquitoes are most active.
  • Wear protective clothing outside, like long sleeves and long pants.
  • Use insect repellent.

Drain standing water from around your home, including in buckets, birdbaths, flowerpots, and tire swings. These are breeding grounds for mosquitoes.

To avoid tick bites:

  • Limit kids' contact with soil, leaves, and vegetation.
  • Have kids wear long-sleeved, light-colored shirts and long pants when outdoors.
  • Check your kids and your pets for ticks when they come inside.

When Should I Call the Doctor?

Call your doctor if your child has a high fever, especially if they have a childhood illness (like measles, mumps, or chickenpox) or are recovering from one.

Get medical care right away if your child has any of these symptoms:

  • a severe headache
  • convulsions (seizures)
  • stiff neck
  • can't look at bright lights
  • double vision
  • trouble walking
  • problems with speech or hearing
  • trouble moving an arm or leg
  • loss of sensation anywhere in the body
  • sudden personality changes
  • problems with memory
  • extreme drowsiness or loss of energy
  • loss of consciousness (passing out)

Get medical care right away if your baby has any of these symptoms:

  • high fever or any fever higher than 100.4°F (38°C) in infants younger than 3 months old
  • fullness or bulging in the soft spot
  • any stiffness
  • floppiness
  • weakness or drowsiness
  • poor appetite or reduced feeding
  • vomiting
  • crying that won't stop

Reviewed by: Yamini Durani, MD
Date Reviewed: Sep 1, 2023

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