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Iowa Department of Health and Human Services

Western Equine Encephalitis (WEE)


Western equine encephalitis (WEE) is a viral disease carried by mosquitoes. WEE occurs in the western parts of the United States, including Iowa and Canada. WEE causes “sleeping sickness” in horses.

WEE is reportable to the Iowa Department of Public Health by Iowa Administrative Code 641 IAC 1.


An infected person may have no symptoms or symptoms may be mild or non-specific. Symptoms usually occur within 5-15 days after being bitten by an infected mosquito and include:

  • Fever
  • Nausea
  • Vomiting
  • Headache
  • Loss of appetite
  • Extreme tiredness
  • Weakness
  • Confusion


Western equine encephalitis is caused by the bite of an infected mosquito.

Risk Factors

Anyone can get western equine encephalitis, but some people are at increased risk:

  • People living in or visiting areas where the disease is common
  • People who work outside or participate in outdoor recreational activities in areas where the disease is common

Western equine encephalitis occurs in all age groups.


Recommendations to reduce the spread of western equine encephalitis include:

  • Avoid mosquito bites
  • Remove all standing water from your property
  • Wear lightweight long-sleeved shirt and long pants when outdoors
  • Personal protection is the best way to prevent exposure to any virus spread by mosquitoes. Review the DEET Fact Sheet and follow the recommendations outlined to reduce your risk of being bitten.
  • Vaccinate your horses


There are no specific drugs available for the treatment of western equine encephalitis. Always consult your health care provider if you have questions about your health or before starting any treatment.

Additional Resources