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What Is Encephalitis?

Encephalitis is inflammation of the brain tissue. Most cases are caused by viral infections. In rare cases it can also be caused by bacteria.

There are two main types of encephalitis—primary and secondary. Primary encephalitis is when a virus directly infects the brain and spinal cord. Secondary encephalitis is when an infection that starts elsewhere travels to your brain.

This disease is rare. According to the Centers for Disease Control, encephalitis occurs in one of every 2,000,000 people (CDC ). Most people who contract it are young children, individuals over 65, or those with weak immune system.

Though rare, the disease is very serious—severe cases can cause death. If you have symptoms of encephalitis, seek medical attention.

The Causes of Encephalitis

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

Common Viruses

The most common virus that causes encephalitis is herpes simplex. Usually the herpes virus travels via a nerve to the skin. There it causes a cold sore. In rare cases, the virus travels to the brain. This form of encephalitis will often affect the temporal lobe—the part of the brain that controls memory and speech. It can also affect the frontal lobe—which affects emotions and behavior. Herpes encephalitis can cause severe damage.

Other common viruses that can cause encephalitis include:

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

Childhood Viruses

The childhood viruses that used to commonly cause encephalitis are now preventable by vaccines. Therefore, these types of encephalitis are rare.

Some childhood viruses that can cause encephalitis include:

  • Chicken pox (very rare)
  • Measles. According to BBC health, measles causes encephalitis in approximately one out of every 1,000 cases. In most cases, the condition is mild. However 20 percent of those affected will have long-term nerve damage. Up to 10 percent of cases are fatal (BBC, 2011 ).
  • Rubella. Approximately one in 5,000 rubella patients develop encephalitis. It is fatal up to 20 percent of the time (BBC, 2011 ).


Arboviruses are viruses carried by insects. The disease they cause depends on the type of insect and what viruses they carry.

  • California encephalitis is transmitted by mosquito bites. It is also known as Lacrosse encephalitis. It mainly affects children. It has few to no symptoms.
  • St. Louis encephalitis occurs in the rural Midwest and southern states. It is generally mild. However, in people over 60, there is a 30 percent mortality rate.
  • West Nile is most often found in Africa and the Middle East. However, it can occur in the US. West Nile is usually relatively mild. It can be fatal among older individuals and those with weakened immune systems.
  • Colorado encephalitis is also called Colorado tick fever. It is transmitted by the female wood tick.
  • Eastern equine encephalitis is spread by mosquitoes. It affects both humans and horses. It is often mild but it does have a two percent mortality rate.
  • Kyasanur forest disease is transmitted by tick bites. It can also be transmitted by drinking raw milk from goats, sheep, or cows. It has a one to two percent mortality rate. People most at risk are hunters, campers, forest workers, and farmers.

Risk Factors for Contracting Encephalitis

The groups most at risk of encephalitis are:

  • older individuals
  • children under 1 year of age
  • people with weakened immune systems.

Living in an area with high mosquito or tick populations also puts you at risk. So does participating in outdoor activities when insects are present.

You are most likely to get encephalitis from an insect bite in the summer or fall.

Symptoms Associated With Encephalitis

The symptoms of encephalitis can range from mild

to severe. Each type can have its own particular set of symptoms.

Mild symptoms include:

Severe symptoms include:

The symptoms in very young children are different. If you see the following symptoms, contact a doctor as soon as possible:

  • vomiting
  • bulging fontanel (soft spot in the scalp)
  • non-stop crying
  • body stiffness
  • lack of appetite

How Is Encephalitis Diagnosed?

The doctor will first ask about your symptoms. If encephalitis is suspected, the following tests may be used:

Spinal Tap Or Lumbar Puncture

In this test, your doctor will collect a sample of spinal fluid. The sample is then tested for signs of infection

Brain Imaging With CT Scan Or MRI

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

Blood Tests

Brain Biopsy

In a biopsy, your doctor will remove small samples of brain to test for infection. This test is rarely performed. There is a high risk of side effects. It is usually only used if doctors cannot tell what is causing the brain swelling and treatments are not working.

How Is Encephalitis Treated?

Anti-viral medications are effective for treating herpes encephalitis. However, they have not yet been shown to work for other forms. Instead, treatment often focuses on relieving symptoms, using:

  • pain killers
  • corticosteroids (to reduce brain inflammation)
  • mechanical ventilation, or breathing treatments
  • lukewarm sponge baths
  • anticonvulsants
  • sedatives (for seizures, restlessness, aggressiveness, and irritability)
  • rest
  • fluids (IV fluids are sometimes necessary)

Sometimes hospitalization is needed to deal with brain swelling and seizures

Complications Associated With Encephalitis

Most people diagnosed with severe encephalitis will experience at least one complication. These can include:

  • loss of memory
  • behavioral/personality changes
  • language and speech problems
  • epilepsy
  • fatigue
  • weakness
  • intellectual disability
  • lack of muscle coordination
  • vision problems
  • problems hearing
  • speech impairment
  • paralysis
  • fatigue
  • coma
  • respiratory distress
  • death

Complications are more likely to develop in certain groups. These include:

  • the elderly
  • those who had coma-like symptoms
  • people who did not get prompt treatment

Long-Term Outlook for Encephalitis

Your prognosis will depend on the severity of the inflammation. Mild cases will disappear in days. Severe cases can take weeks to months to get better. Some can cause permanent brain damage. You may experience:

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

According to BBC Health, recovery may include:

  • physical therapy - to improve strength, motor coordination, balance, and flexibility
  • occupational therapy - to help redevelop every day skills
  • speech therapy - to help you relearn muscle control needed for talking
  • psychotherapy - to help with coping strategies, mood disorders, or personal changes (BBC, 2011 ).

Can Encephalitis be Prevented?

Some, but not all, cases of encephalitis are preventable. Effective ways to reduce risk include:

  • making certain children receive all scheduled vaccinations
  • getting vaccinated for encephalitis, where available
  • always using mosquito repellant when outside
  • wearing long sleeves and pants in areas with large tick and mosquito populations
  • keeping standing water away from your house

Category: Cytomegalovirus

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