What is encephalitis?

Encephalitis is an inflammation of the brain tissue. The most common cause is viral infections. In rare cases it can be caused by bacteria or even fungi.

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 are the symptoms of encephalitis?

The symptoms of encephalitis can range from mild to severe.

Mild symptoms include:

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

Severe symptoms include:

  • fever of 103°F (39.4°C) 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 any of the following:

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


What causes encephalitis?

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 travels to the brain.

This form of encephalitis usually affects 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 and death.

Other common viruses that can cause encephalitis include:

  • mumps
  • Epstein-Barr virus
  • HIV
  • cytomegalovirus

Childhood viruses

Vaccines can prevent the childhood viruses that used to cause encephalitis. Therefore, these types of encephalitis are rare today. Some childhood viruses that can cause encephalitis include:

  • chicken pox (very rare)
  • measles
  • rubella


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

  • California encephalitis (also called La Crosse encephalitis) is 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 is 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) is transmitted by the female wood tick. It’s typically a mild disease, and most people will recover quickly.
  • Eastern equine encephalitis is spread by mosquitoes. It affects both humans and horses. Although rare, it has a 33 percent mortality rate.
  • Kyasanur forest disease is 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.

Visit http://www.healthline.com/health/encephalitis#overview1 to learn more.

Johnson, S. (2017, March 31). Encephalitis. Retrieved May 10, 2017, from http://www.healthline.com/health/encephalitis#overview1

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