Mosquito-Borne Viral Encephalitis
Encephalitis is inflammation of the brain. Certain mosquito-borne viruses can lead to encephalitis. Examples of these viruses include:
- West Nile encephalitis
- Eastern equine encephalitis
- Western equine encephalitis
- St. Louis encephalitis
- La Crosse encephalitis
- Japanese encephalitis
- Venezuelan equine encephalitis
The most common cause is being bitten by an infected mosquito. There are other, rarer causes, such having a blood transfusion with infected blood.
The greatest risk factors are spending time in areas where mosquitoes are present and not using insect repellent.
People who are age 50 years and older and those with a weakened immune system have a higher risk of developing serious symptoms.
Most people who become infected with one of these mosquito-borne viruses do not develop any symptoms.
If symptoms do occur, they are generally mild and may include flu-like symptoms, such as:
- Joint and muscle pain
While rare, a small percentage of people develop encephalitis and have serious, life-threatening symptoms, such as:
In addition to taking your medical history and doing a physical exam, your doctor will ask you:
- What kind of symptoms you are experiencing
- Where you have been living or traveling to
- Whether you have been exposed to mosquitoes
A blood test is commonly used to confirm the diagnosis of a mosquito-borne virus. Depending on the symptoms that you have, your doctor may order other tests, such as:
Treatment focuses on supportive care, such as taking pain-relieving medicines and replenishing fluids so that you are not dehydrated.
Severe symptoms require hospitalization, which may include:
- Mechanical ventilation (breathing support)
- Fluids given intravenously (through a vein in your arm)
- Medicine to control seizures
- Medicine to decrease brain swelling
The best way to reduce your chances of getting mosquito-borne viral encephalitis is to avoid being bitten by mosquitoes. Steps that can help include:
- Limiting outside activities where mosquitoes are present
- Wearing long sleeve shirts and long pants at dusk and dawn, when mosquitoes are most active
- Using bug repellent that contains DEET
- Emptying sources of standing water around the home, such as bird baths and gutters, where mosquitoes may breed
- Use proper mosquito netting at night. Look for netting treated with insecticide.
- Repairing screens on your windows and doors to prevent mosquitoes from getting into your house
Mosquitoes can contract viruses by biting infected birds. If you see a dead bird, call the public health department. Do not touch the dead bird unless you are wearing disposable gloves.
Centers for Disease Control and Prevention
National Institute of Neurological Disorders and Stroke
Eastern equine encephalitis. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/easternequineencephalitis/. Updated August 16, 2012. Accessed September 24, 2012.
Eastern equine encephalitis. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated July 13, 2012. Accessed September 24, 2012.
Encephalitis: an overview. EBSCO Nursing Reference Center website. Available at: http://www.ebscohost.com/pointOfCare/nrc-about. Updated March 9, 2012. Accessed September 24, 2012.
Meningitis and encephalitis fact sheet. National Institute of Neurological Disorders and Stroke website. Available at: http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm. Updated February 16, 2011. Accessed September 24, 2012.
Mosquito-borne encephalitis. Orange County Vector Control District website. Available at: http://www.ocvcd.org/bulletins/Mosquito-Borne%20Encephalitis.pdf. Accessed September 24, 2012.
Quick lesson about West Nile infection. EBSCO Nursing Reference Center website. Available at: http://www.ebscohost.com/pointOfCare/nrc-about. Updated September 7, 2012. Accessed September 24, 2012.
Reimann CA, Hayes EB, DiGuiseppi C, et al. Epidemiology of neuroinvasive arboviral disease in the United States, 1999-2007. Am J Trop Med Hyg. 2008;79(6):974-979.
Technical fact sheet: eastern equine encephalitis. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/EasternEquineEncephalitis/tech/factSheet.html. Updated August 16, 2012. Accessed September 24, 2012.
West Nile virus infection. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated September 13, 2012. Accessed September 24, 2012.
West Nile virus: what you need to know. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvbid/westnile/wnv_factSheet.htm. Updated September 12, 2012. Accessed September 24, 2012.
10/1/2013 DynaMed Systematic Literature Surveillance http://www.dynamicmedical.com/what.php: Reimer LJ, Thomsen EK, Tisch DJ, et al. Insecticidal bed nets and filariasis transmission in Papua New Guinea. N Eng J Med. 2013 Aug 22; 369(8):745-53.
Last reviewed November 2012 by Michael Woods, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.