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Definition

Western equine encephalitis (WEE) is a viral infection spread by infected mosquitoes. This disease can affect the central nervous system, causing severe complications and even death.

The Central Nervous System

Causes

WEE is caused by the aptly named western equine encephalitis virus, which is one of a group of viruses called arboviruses. In the United States, these viruses are usually spread by mosquitoes that are infected.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. Some factors thought to increase the risk of WEE include:

Living in or visiting the plains regions of the western and central United States
Working outdoors
Participating in outdoor activities

Symptoms

WEE results in a wide range of symptoms, and may produce no symptoms at all. The disease can be mild, severe, or even fatal. The disease is fatal in about 3% of people who develop symptoms. Symptoms associated with WEE usually appear 5-10 days after the bite of an infected mosquito, and may include:

Headache
Fever
Drowsiness
Irritability
Nausea
Vomiting
Confusion
Weakness
Coma
Seizures (in young infants)

Diagnosis

Your doctor will ask about your symptoms and medical history, and perform a physical exam. Other tests may include:

Blood tests
Spinal fluid tests

Treatment

Because the infection is viral, there is no specific treatment for WEE. Treatment will focus on managing your symptoms and related complications.

Prevention

There is no vaccine against WEE for humans, although there is a vaccine for horses. Prevention of WEE focuses on controlling mosquitoes and avoiding mosquito bites. Steps you can take to avoid mosquito bites include:

Stay inside between dusk and dark, when mosquitoes are most active.
Wear long pants and long-sleeved shirts when outside.
Spray exposed skin with an insect repellent that contains up to 35% diethyltoluamide (DEET).

RESOURCES:

Centers for Disease Control and Prevention

http://www.cdc.gov

Directors of Health Promotion and Education

http://www.dhpe.org

CANADIAN RESOURCES:

Canadian Centers for Occupational Health and Safety

http://www.ccohs.ca

Canadian Cooperative Wildlife Health Centre

http://wildlife1.usask.ca

References:

Western equine encephalitis. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvbid/arbor/weefact.htm . Accessed July 3, 2007.

Western equine encephalitis. Directors of Health Promotion and Education website. Available at: http://www.dhpe.org/wee.asp . Accessed July 3, 2007.

Last reviewed August 2007 by David L. Horn, MD, FACP

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.

Western Equine Encephalitis