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:
- West Nile encephalitis
- Eastern equine encephalitis
- Western equine encephalitis
- St. Louis encephalitis
- La Crosse encephalitis
- Japanese encephalitis
- Venezuelan equine encephalitis
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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.
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
- Being tired
- Joint and muscle pain
A small number of people develop encephalitis. Symptoms can be serious and even fatal. They may be:
- High fever
- Not being able to move
- Vision loss
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
Severe symptoms need hospital care. This may include:
- IV fluids
- Medicines to:
- Stop seizures
- Reduce brain swelling
- Mechanical ventilation—to help with breathing
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
Centers for Disease Control and Prevention
National Institute of Neurological Disorders and Stroke
Alberta Ministry of Health
Alpern JD, Dunlop SJ, et al. Personal protection measures against mosquitoes, ticks, and other arthropods. Med Clin North Am. 2016;100(2):303-16.
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Last reviewed December 2020 by EBSCO Medical Review Board David L. Horn, MD, FACP Last Updated: 4/6/2021