Definition

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

Causes

The most common cause is being bitten by an infected mosquito. There are other, rarer causes, such having a blood transfusion with infected blood.

Risk Factors

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.

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:

• Headache
• Fever
• Chills
• Fatigue
• Joint and muscle pain
• Vomiting

While rare, a small percentage of people develop encephalitis and have serious, life-threatening symptoms, such as:

• High fever
• Disorientation
• Vision loss
• Paralysis
• Seizures
• Coma

Diagnosis

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:

• MRI scan
• CT scan
• Cerebrospinal fluid tests to evaluate the fluid that surrounds the brain and spinal cord

Treatment

Treatment focuses on supportive care, such as taking pain-relieving medications and replenishing fluids so that you are not dehydrated.

Severe symptoms require hospitalization, which may include:

• Breathing support— mechanical ventilation
• IV fluids
• Antiseizure medications
• Medications to decrease brain swelling

Prevention

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.

National Institute of Neurological Disorders and Stroke http://www.ninds.nih.gov

Healthy Alberta http://www.healthyalberta.com

Eastern equine encephalitis. EBSCO DynaMed website. Available at:
http://www.ebscohost.com/dynamed
Updated July 13, 2012. Accessed September 24, 2012.

Encephalitis: an overview. EBSCO Nursing Reference Center website. Available at:
http://www.ebscohost.com/nursing/products/nursing-reference-center
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/nursing/products/nursing-reference-center
Updated September 7, 2012. Accessed September 24, 2012.

Reimann CA, Hayes EB, 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:
http://www.ebscohost.com/dynamed
Updated September 13, 2012. Accessed September 24, 2012.

West Nile virus. Centers for Disease Control and Prevention website. Available at:
http://www.cdc.gov/westnile/index.html
Updated September 12, 2012. Accessed September 24, 2012.

10/1/2013 DynaMed Systematic Literature Surveillance
http://www.ebscohost.com/dynamed:
Reimer LJ, Thomsen EK, et al. Insecticidal bed nets and filariasis transmission in Papua New Guinea. N Eng J Med. 2013;369(8):745-753.