Western Equine Encephalitis
all information

Western Equine Encephalitis

En Español (Spanish Version)


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


© 2008 Nucleus Medical Art, Inc.


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

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


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)


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


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


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).


Centers for Disease Control and Prevention

National Library of Medicine


Canadian Centers for Occupational Health and Safety

Canadian Cooperative Wildlife Health Centre


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 April 2008 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.

Your Health and Happiness