What is encephalitis?

Encephalitis is inflammation of the brain. The inflammation causes the brain to swell, which leads to changes in neurological function, resulting in mental confusion and seizures.

What causes encephalitis?

The cause of encephalitis depends on the season, the area of the country, and the type of exposure. Viruses are the leading cause of encephalitis. Although vaccines for many viruses, including measles, mumps, rubella, and chickenpox have greatly lowered the rate of encephalitis from these diseases, other viruses can cause encephalitis. These include herpes simplex virus and rabies.

Encephalitis can also occur following infection by disease-carrying agents including ticks (Lyme disease), mosquitoes (West Nile virus), and cats (toxoplasmosis). Encephalitis can also be caused by a bacterial infection.

What are the symptoms of encephalitis?

Encephalitis often follows a viral illness such as an upper respiratory infection, or a gastrointestinal illness, that may cause diarrhea, nausea, or vomiting. The following are the most common symptoms of encephalitis. However, each person may experience symptoms differently. Symptoms may include:

  • Headache
  • Mild flu-like symptoms (aches, fatigue, slight fever)
  • Sensitivity to light
  • Neck stiffness
  • Sleepiness or lethargy
  • Increased irritability
  • Seizures
  • Changes in alertness, confusion, or hallucinations
  • Loss of energy
  • Loss of appetite
  • Unsteady gait
  • Nausea and vomiting

In severe cases, symptoms may include:

  • Weakness or partial paralysis in the arms and legs
  • Double vision
  • Impairment of speech and/or hearing
  • Coma

The symptoms of encephalitis may resemble other problems or medical conditions. Always consult your health care provider for a diagnosis.

How is encephalitis diagnosed?

The diagnosis of encephalitis is made after the sudden or gradual onset of specific symptoms and after diagnostic testing. During the exam, your health care provider will ask about your medical history, including what immunizations you’ve had. Your health care provider may also ask if you have recently had a cold or other respiratory illness, or a gastrointestinal illness, and if you have recently had a tick bite, have been around pets or other animals, or have traveled to certain areas of the country.

Diagnostic tests that may be performed to confirm the diagnosis of encephalitis may include the following:

  • Magnetic resonance imaging (MRI). This procedure uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
  • Computed tomography scan (also called a CT or CAT scan). This imaging procedure uses a combination of X-rays and computer technology to produce horizontal, or axial, images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general X-rays.
  • Blood tests. In this test, the blood is examined for signs of infection.
  • Urine and stool tests. In this test, the urine and stool samples are examined for infection.
  • Sputum culture. This test is done on the material that is coughed up from the lungs and into the mouth. A sputum culture is often performed to determine if an infection is present.
  • Electroencephalogram (EEG). This procedure records the brain's continuous, electrical activity using electrodes attached to the scalp.
  • Spinal tap (also called a lumbar puncture). For this test, a special needle is placed into the lower back, into the spinal canal. This is the area around the spinal cord. The pressure in the spinal canal and brain can then be measured. A small amount of cerebral spinal fluid (CSF) can be removed and sent for testing to determine if there is an infection or other problems. CSF is the fluid that bathes the brain and spinal cord.


  • Brain biopsy. This procedure involves removing tissue or cells from the body for examination under a microscope; in rare cases, a biopsy of affected brain tissue may be removed for diagnosis.
  • Intracranial pressure monitoring (ICP). This test measures the pressure inside the skull. If there is a severe brain injury, head surgery, brain infection, or other problems, the brain may swell. Since the brain is covered by the skull, there is only a small amount of room for it to swell. This means that, as the brain swells, the pressure inside the skull goes up. If the pressure gets significantly higher than normal, it can cause damage to the brain. Intracranial pressure is measured in two ways. One way is to place a small, hollow tube (catheter) into the fluid-filled space in the brain (ventricle). Other times, a small, hollow device (bolt) is placed through the skull into the space just between the skull and the brain. Both devices are inserted in the intensive care unit (ICU) or in the operating room. The ICP device is then attached to a monitor that gives a constant reading of the pressure inside the skull. If the pressure goes up, it can be treated right away. While the ICP device is in place, you will be given medication to stay comfortable. When the swelling has gone down and there is little chance of more swelling, the device will be removed.

How is encephalitis treated?

Specific treatment for encephalitis will be determined by your health care provider based on:

  • Your age, overall health, and medical history
  • Extent of the condition
  • Your tolerance for specific medications, procedures, or therapies
  • Expectations for the course of the condition
  • Your opinion or preference

The key to treating encephalitis is early detection and treatment. A person with encephalitis requires immediate hospitalization and close monitoring.

The goal of treatment is to reduce the swelling in the head and to prevent other related complications. Medications to control the infection, seizures, fever, or other conditions may be used.

What are the complications of encephalitis?

Complications of encephalitis depend on the severity of inflammation and whether you have other organ problems. In severe cases, a breathing machine may be needed to help you breathe easier. In some severe cases, the disease progresses rapidly resulting in death. Mild cases are usually short and result in a full recovery. Unfortunately, severe cases can cause permanent impairment including fatigue, irritability, impaired concentration, seizures, hearing loss, memory loss, and blindness.

Can encephalitis be prevented?

These measures can help prevent encephalitis:

  • Keep your immunizations up to date. Vaccines are an important part of preventing encephalitis. Vaccines for viruses such as measles, mumps, rubella, and chickenpox have greatly lowered the rate of encephalitis from these diseases.
  • Use proper hygiene and hand washing to help prevent the spread of viruses and encephalitis.
  • Avoid mosquito and tick exposure to reduce the incidence of encephalitis.


If you are exposed to someone with bacterial encephalitis, you may be offered a course of antibiotics to prevent you from getting the disease.

Living with encephalitis

As you recover, physical, occupational, or speech therapy may be necessary to help regain muscle strength and/or speech skills.

Loved ones can be educated on how to best care for you at home. You will require frequent medical evaluations following hospitalization.

When should I call my health care provider?

You should contact your health care provider if there are signs of another infection including:

  • Headache
  • Fever
  • Neck stiffness

Also, signs of neurological involvement such as:

  • Seizures
  • Memory loss
  • Visual difficulties
  • Impaired hearing
  • Behavioral changes

Key points

  • Encephalitis is inflammation of the brain.
  • Encephalitis is most commonly caused by a virus.
  • Headache, stiff neck, and sensitivity to light are common symptoms.
  • Encephalitis can be deadly and prompt treatment is crucial for full-recovery.
  • Most people recover fully but severe cases can lead to long-term complications.
  • Preventing encephalitis includes up to date vaccinations, good hygiene, and avoiding ticks and mosquitoes.

Next steps

Tips to help you get the most from a visit to your health care provider:

  • Before your visit, write down questions you want answered.
  • Bring someone with you to help you ask questions and remember what your provider tells you.
  • At the visit, write down the names of new medicines, treatments, or tests, and any new instructions your provider gives you.
  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your provider if you have questions.

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