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Health Information Center

Mosquito-Borne Viral Encephalitis

  • Amy Scholten, MPH
Publication Type:


Mosquito-Borne Viral Encephalitis


Mosquito-borne viral encephalitis is inflammation of the brain. This condition is from viruses carried by mosquitoes. Examples of these viruses are:


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The most common cause is a bite from an infected mosquito. Rarely, there may be other causes. One example is a blood transfusion with infected blood.

Risk Factors

Things that raise the risk are:

  • Being outdoors—in areas with mosquitoes
  • Not using bug spray

The risk of serious symptoms is highest in those age 50 years and older. It is also higher in those with weak immune systems.


Most people with viruses from mosquitoes do not have symptoms.

If symptoms happen, they are often mild. They may be:

  • Fever and chills
  • Headache
  • Being tired
  • Joint and muscle pain
  • Vomiting

A small number of people develop encephalitis. Symptoms can be serious and even fatal. They may be:

  • High fever
  • Confusion
  • Seizures
  • Not being able to move
  • Vision loss
  • Coma


The doctor will ask about your symptoms, travel, and health history. A physical exam will be done.

Blood tests will be done. They are often used to diagnose viruses from mosquitoes. The doctor may also order other tests, such as:


Treatment focuses on support, such as:

  • Pain medicines
  • Fluids

Severe symptoms need hospital care. This may include:


The risk of mosquito-borne viral encephalitis can be reduced. The best way is to avoid mosquito bites. Things that may help are:

  • Covering up the skin
  • Using bug sprays, netting, and screens
  • Staying inside between dusk and dark




  • Alpern JD, Dunlop SJ, et al. Personal protection measures against mosquitoes, ticks, and other arthropods. Med Clin North Am. 2016;100(2):303-16.
  • Eastern equine encephalitis. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/easternequineencephalitis. Accessed April 6, 2021.
  • Eastern equine encephalitis. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/eastern-equine-encephalitis. Accessed April 6, 2021.
  • Encephalitis: an overview. EBSCO Nursing Reference Center website. Available at: http://www.ebscohost.com/nursing/products/nursing-reference-center. Accessed April 6, 2021.
  • Meningitis and encephalitis information page. National Institute of Neurological Disorders and Stroke website. Available at: https://www.ninds.nih.gov/Disorders/All-Disorders/Meningitis-and-Encephalitis-Information-Page. Accessed April 6, 2021.
  • Mosquito avoidance. EBSCO DynaMed website. Available at: https://www.dynamed.com/prevention/mosquito-avoidance. Accessed April 6, 2021.
  • Quick lesson about West Nile infection. EBSCO Nursing Reference Center website. Available at: https://www.ebscohost.com/nursing/products/nursing-reference-center. . Accessed April 6, 2021.
  • West Nile virus infection. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/west-nile-virus-infection. Accessed April 6, 2021.
  • West Nile virus. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/westnile/index.html. Accessed April 6, 2021.


  • David L. Horn, MD, FACP
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.