What Is Encephalitis?

Encephalitis is an inflammation of the brain tissue. It’s most often caused by viral infections. In some cases, bacterial infections can cause encephalitis.

There are two main types of encephalitis: primary and secondary. Primary encephalitis occurs when a virus directly infects the brain and spinal cord. Secondary encephalitis occurs when an infection starts elsewhere in the body and then travels to your brain.

Encephalitis is a rare yet serious disease that can be life-threatening. You should call your doctor immediately if you have symptoms of encephalitis.

What Causes Encephalitis?

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Many different viruses can cause encephalitis. It’s helpful to categorize the potential causes into three groups: common viruses, childhood viruses, and arboviruses.

Common Viruses

The most common virus that causes encephalitis in developed countries is herpes simplex. The herpes virus typically travels through a nerve to the skin, where it causes a cold sore. In rare cases, however, the virus goes to the brain.

This form of encephalitis will often damage the temporal lobe (the part of the brain that controls memory and speech). It can also affect the frontal lobe (the part that controls emotions and behavior). Encephalitis caused by herpes is dangerous and can lead to severe brain damage.

Other common viruses that can cause encephalitis include:

  • mumps
  • Epstein-Barr virus
  • HIV
  • cytomegalovirus (CMV)

Childhood Viruses

Vaccines prevent the childhood viruses that used to commonly cause encephalitis. Therefore, these types of encephalitis are rare today.

Some childhood viruses that can cause encephalitis include:


Arboviruses are viruses carried by insects. The type of arbovirus that’s transmitted depends on the insect. Below are different types:

  • California encephalitis (also called La Crosse encephalitis): transmitted through mosquito bites and mainly affects children. It causes few to no symptoms.
  • St. Louis encephalitis: occurs in the rural Midwest and southern states. It’s generally a mild virus and causes few symptoms.
  • West Nile virus: most often found in Africa and the Middle East. However, it can occur in the United States. It’s usually relatively mild, causing flu-like symptoms. However, it can be fatal among older adults and people with weak immune systems.
  • Colorado encephalitis (also called Colorado tick fever): transmitted by the female wood tick. It’s typically a mild disease, and most people will recover quickly.
  • Eastern equine encephalitis: spread by mosquitoes. It affects both humans and horses. Although rare, it has a 33 percent mortality rate.
  • Kyasanur forest disease: transmitted through tick bites. People can also get it by drinking raw milk from goats, sheep, or cows. Hunters, campers, and farmers are most at risk for getting this disease.

What Are the Risk Factors for Encephalitis?

Risk Factors

The groups most at risk of encephalitis are:

  • older adults
  • children under the age of 1
  • people with weak immune systems

You may also have a higher risk of getting encephalitis if you live in an area where mosquitos or ticks are common.

You’re more likely to get encephalitis from an insect bite in the summer or fall.

What Are the Symptoms of Encephalitis?

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The symptoms of encephalitis can range from mild to severe.

Mild symptoms include:

  • fever
  • headache
  • vomiting
  • stiff neck
  • lethargy (exhaustion)

Severe symptoms include:

  • very high fever (103°F or higher)
  • confusion
  • drowsiness
  • hallucinations
  • slower movements
  • coma
  • seizures
  • irritability
  • sensitivity to light
  • unconsciousness

Infants and young children show different symptoms. Call a doctor immediately if your child is experiencing the following signs:

  • vomiting
  • bulging fontanel (soft spot in the scalp)
  • constant crying
  • body stiffness
  • poor appetite

How Is Encephalitis Diagnosed?

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Your doctor will first ask you about your symptoms. They may perform the following tests if encephalitis is suspected.

Spinal Tap or Lumbar Puncture

In this test, your doctor will collect a sample of spinal fluid and test it for signs of infection.

Brain Imaging with CT Scan or MRI

These tests detect changes in brain structure. They can rule out other possible explanations for symptoms, such as a tumor or stroke.

Electroencephalograph (EEG)

An EEG uses electrodes (small metal discs with wires) attached to the scalp to record brain activity.

Blood Tests

A blood test can reveal signs of a viral infection.

Brain Biopsy

In a brain biopsy, your doctor will remove small samples of brain tissue to test for infection. This procedure is rarely performed because there’s a high risk of complications. It’s usually only done if doctors can’t determine the cause the brain swelling or if treatment isn’t working.

How Is Encephalitis Treated?

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Anti-viral medications can help treat herpes encephalitis. However, they aren’t effective in treating other forms of encephalitis. Instead, treatment often focuses on relieving symptoms. These treatments may include:

  • rest
  • pain killers
  • corticosteroids (to reduce brain inflammation)
  • mechanical ventilation (to help with breathing)
  • lukewarm sponge baths
  • anticonvulsants (to prevent or stop seizures)
  • sedatives (for restlessness, aggressiveness, and irritability)
  • fluids (sometimes through an IV)

You may need to be hospitalized during treatment, especially with brain swelling and seizures.

What Are the Complications Associated with Encephalitis?

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Most people who are diagnosed with severe encephalitis will experience complications. Complications resulting from encephalitis can include:

  • loss of memory
  • behavioral/personality changes
  • epilepsy
  • fatigue
  • physical weakness
  • intellectual disability
  • lack of muscle coordination
  • vision problems
  • hearing problems
  • speaking issues
  • fatigue
  • coma
  • difficulty breathing
  • death

Complications are more likely to develop in certain groups, such as:

  • older adults
  • people who have had coma-like symptoms
  • people who didn’t get treatment right away

What Is the Long-Term Outlook for Someone with Encephalitis?

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Your outlook will depend on the severity of the inflammation. In mild cases of encephalitis, the inflammation will likely disappear in a few days. However, severe cases may require weeks or months to get better. It can sometimes cause permanent brain damage or even death.

People with encephalitis may also experience:

  • paralysis
  • loss of brain function
  • problems with speech, behavior, memory, and balance

Depending on the type and severity of encephalitis, it may be necessary to receive additional therapy, including:

  • physical therapy: to improve strength, coordination, balance, and flexibility
  • occupational therapy: to help redevelop everyday skills
  • speech therapy: to help relearn muscle control needed for talking
  • psychotherapy: to help with coping strategies, mood disorders, or personality changes

Can Encephalitis Be Prevented?

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Encephalitis isn’t always preventable, but you can lower your risk by getting vaccinated for encephalitis, where available. You should also make sure your children receive vaccinations for the viruses that can cause encephalitis. When outside, it’s important to use mosquito repellant. Wear long sleeves and pants in areas where ticks and mosquitos are common.

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