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Bacterial & Viral Infections


Encephalitis literally means an inflammation of the brain. In most cases, this inflammation is caused by a virus. Encephalitis is a rare disease that occurs in approximately 0.5 per 100,000 individuals — most commonly in children, the elderly, and people with weakened immune systems (e.g., those with HIV/AIDS or cancer).

Although several thousand cases of encephalitis (also called acute viral encephalitis or aseptic encephalitis) are reported to the Centers for Disease Control and Prevention (CDC) every year, experts suspect that many more go unreported because the symptoms can be very broad.

Signs and Symptoms

Symptoms in milder cases of encephalitis usually include:

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

In more severe cases of encephalitis, a person is more likely to experience high fever and any of a number of symptoms that relate to the central nervous system, including:

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

It’s harder to detect some of these symptoms in infants, but important signs to look for include:

  • vomiting
  • a full or bulging soft spot (fontanel)
  • crying that doesn’t stop or that seems worse when an infant is picked up or handled
  • body stiffness

Because encephalitis can follow or accompany common viral illnesses, there sometimes are signs and symptoms of these illnesses beforehand. But often, the encephalitis appears without warning.


Because encephalitis can be caused by many types of germs, the infection can be spread in several different ways.

One of the most dangerous and most common causes of encephalitis is the herpes simplex virus (HSV). HSV is the same virus that causes cold sores around the mouth, but when it attacks the brain it may occasionally be fatal. Fortunately, HSV encephalitis is very rare.

Encephalitis can be a very rare complication of Lyme disease transmitted by ticks or of rabies spread by rabid animals.

Mosquitoes can also transmit the viruses for several types of encephalitis, including West Nile encephalitis, St. Louis encephalitis, and Western Equine encephalitis. Over the last several years in the United States, there’s been concern about the spread of West Nile virus, which is transmitted to humans by mosquitoes that pick up the virus by biting infected birds.

Milder forms of encephalitis can follow or accompany common childhood illnesses, including measles, mumps, chickenpox, rubella (German measles), and mononucleosis. Viruses like chickenpox spread mostly via the fluids of the nose and throat, usually during a cough or sneeze.

Less commonly, encephalitis can result from a bacterial infection, such as bacterial meningitis, or it may be a complication of other infectious diseases like syphilis. Certain parasites, like toxoplasmosis (found in infected cat feces), can also cause encephalitis in people with weakened immune systems.


Brain inflammation itself is not contagious, but any of the various viruses that cause encephalitis can be. Of course, just because someone gets a certain virus does not mean that he or she will develop encephalitis. Still, to be safe, avoid contact with anyone who has encephalitis.


Encephalitis cannot be prevented, but you can try to avoid the illnesses that may lead to it. Many common childhood illnesses are largely preventable through immunization, so follow the immunization schedule recommended by your child’s doctor. Kids should also avoid contact with anyone who already has encephalitis.

In areas where encephalitis can be transmitted by insect bites, especially mosquitoes, kids should:

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

Also, all standing water around your home should be drained, including buckets, birdbaths, flowerpots, and tire swings because 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 frequently for ticks.


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


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 abnormalities
  • electroencephalogram (EEG), which records the electrical signals in the brain, to check for abnormal brain waves
  • blood tests to confirm the presence of bacteria or viruses in the blood, and whether a person is producing antibodies (specific proteins that fight infection) in response to a germ
  • lumbar puncture, or spinal tap, in which cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) is checked for signs of infection


Some kids with very mild encephalitis can be monitored at home, but most will need care in a hospital, usually in an intensive care unit (ICU). Doctors will carefully monitor their blood pressure, heart rate, and breathing, as well as their body fluids, to prevent further swelling of the brain.

Because antibiotics aren’t effective against viruses, they aren’t used to treat most forms of encephalitis. However, antiviral drugs can be used to treat some forms of encephalitis, especially the type caused by the herpes simplex virus. Corticosteroids may also be used in some cases to reduce brain swelling. If a child is having seizures, anticonvulsants might be given. Over-the-counter (OTC) medications, like acetaminophen, can be used to treat fever and headaches.

Many people with encephalitis make a full recovery. In some cases, swelling of the brain can lead to permanent brain damage and lasting complications like learning disabilities, speech problems, memory loss, or lack of muscle control. Speech, physical, or occupational therapy may be needed in these cases. It’s difficult to predict the outcome for each patient at the time the illness begins, but some types of encephalitis are known to cause more serious complications, such as Japanese encephalitis.

Rarely, if the brain damage is severe, encephalitis can lead to death. Infants (younger than 1 year old) and adults over 55 are at greatest risk of death from encephalitis.

When to Call the Doctor

Call your doctor if your child has a high fever, especially if he or she also has a childhood illness (measles, mumps, chickenpox) or is recovering from one.

Seek immediate medical attention if your child has any of the following symptoms:

  • severe headache
  • convulsions (seizures)
  • stiff neck
  • inability to look at bright lights
  • double vision
  • difficulty walking
  • problems with speech or hearing
  • difficulty moving an arm or leg
  • loss of sensation anywhere in the body
  • sudden personality changes
  • problems with memory
  • extreme drowsiness or lethargy
  • loss of consciousness

If your infant has any of the following symptoms, seek immediate medical care:

  • high fever or any fever higher than 100.4ºF (38ºC) in infants younger than 3 months old
  • fullness or bulging in the soft spot
  • any stiffness
  • floppiness or decreased tone
  • lethargy
  • poor appetite or reduced feeding
  • vomiting
  • crying that won’t stop

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