Eastern Equine Encephalitis Michigan horse health alert

Christine Skelly<skellych@msu.edu> and Thomas Guthrie<guthri19@msu.edu>, Michigan State University Extension -

MDARD confirms first case of Eastern equine encephalitis for 2024 in a Van Buren County Horse.

brown horse standing near a white building
Access to a simple shelter or shady trees during dawn and dusk can help protect horses from mosquito bites, reducing their risk of contracting Eastern equine encephalitis or West Nile virus. Photo by Chris Skelly, MSU Extension.

The Michigan Department of Agriculture and Rural Development (MDARD) reported Michigan’s first case of Eastern equine encephalitis (EEE) in a domestic animal for 2024. The disease was detected in a Standardbred filly from Van Buren County; the horse was unvaccinated against EEE. 

“While this is the first case of EEE detected this season, other mosquito-borne diseases have been discovered throughout Michigan, including one human case of West Nile virus,” State Veterinarian Dr. Nora Wineland, DVM, MS, DACVPM, said. “These detections clearly indicate disease is circulating in the state’s mosquito population, making it crucial to protect animals and people against these insects. Preventing mosquito bites will prevent mosquito-borne diseases.”

Read the full report at MDARD News, August 7, 2024.

Encephalomyelitis is a disease that causes brain and spinal cord inflammation, usually caused by an infectious agent. There are three variants of equine encephalomyelitis: Eastern (EEE), Western (WEE), and Venezuelan (VEE). All three variants are transmitted primarily by mosquitoes. All three can be serious, but EEE has a much higher fatality rate than the others. 

The most important and effective prevention step for Michigan horses is to vaccinate horse(s) for EEE annually prior to the vector season. Vaccination for EEE typically provides protection for six months and is included in the annual core vaccinations that the American Association of Equine Practitioners recommends for all equids. Owners can still vaccinate horses for EEE and West Nile Virus (WNV) for this year’s mosquito season. Equids in southern Michigan that were vaccinated in the early spring may benefit from a booster to protect them for the entire mosquito season. Michigan State University Extension advises owners to work with their veterinarian to determine the best vaccination schedule for their particular area.

MSU Extension advice for horse, pony, donkey and mule owners 

  • Work with their veterinarian to ensure their equids' core vaccinations (including EEE and WNV) are current. 
  • Remove sources of standing water in pastures and around the barn and change drinking water sources daily.
  • Apply insect repellent that is approved for equids to horses as recommended.
  • Keep horses indoors around dawn and dusk when mosquitoes are most active, or ensure they have a well-ventilated shady spot to avoid mosquitoes.
  • Utilize fans or open windows to create a breeze in the barn for stalled animals.

Signs or symptoms of EEE

  • High fever (temperature higher than 103 degrees Fahrenheit)
  • Depression and lack of appetite
  • Pressing the head into corners
  • Walking around aimlessly, often in circles
  • Blindness
  • An uncoordinated gait, staggering
  • Recumbency, unable to get up
  • Seizures
  • Death

Contact your veterinarian immediately if your horse has any of these symptoms or issues. If EEE or West Nile virus (WNV) is suspected of having infected your horse, it should be reported to MDARD at 800-292-3939 (daytime) or 517-373-0440 (after-hours emergencies).

Mosquitoes transmit EEE and WNV to horses and humans. Neither virus is transferred between horses or between horses and humans.  Be sure to protect yourself from mosquito-borne diseases by following CDC guidelines.

Before going outside

For more information on equine diseases, visit MDARD’s website at www.michigan.gov/equinediseases. Updates on EEE and WNV cases in Michigan will be posted to the Equine Disease Communication Center’s Outbreak Alerts. For more information on how EEE may impact human health, please visit the Centers for Disease Control and Prevention website.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

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