Update: Eastern equine encephalitis reported in Michigan horses

Vaccinate your horse to protect it from getting sick from eastern equine encephalitis.

Young horses are often more susceptible to eastern equine encephalitis (EEE).

The Michigan Department of Agriculture and Rural Development (MDARD) recently received confirmation that an additional horse was diagnosed with eastern equine encephalitis (EEE) virus. This brings the total number of reported cases of EEE in Michigan for 2019 to 10. To date, all positive cases in 2019 in Michigan have been in unvaccinated horses. Disease trends did predict that higher than normal numbers would be seen in 2019, in addition to increased rainfall in spring and summer leading to an increase in mosquito numbers.

Facts about EEE:

  • Transmission of EEE is by infected mosquitoes.
  • Birds can serve as a host after having been bitten by an infected mosquito.   
  • The virus spreads through the body and attacks the central nervous system (brain and spinal cord).
  • All horses are at risk. However, younger horses (six months to two years of age) are more vulnerable. 
  • The virus is not spread by direct contact between horses.
  • Death of horses infected with EEE is relatively high (80 percent or more of cases)  

Ways to help prevent EEE

Michigan State University Extension suggests that prevention remains the best practice to follow. The following is a list of considerations.

  • Vaccinate your horse(s) for EEE. This is ultimately the most important step to prevention. Vaccination typically provides protection for six to nine months. Your veterinarian will be your best resource for determining vaccination schedules for your respective area. 
  • Keep horses indoors around dawn and dusk when mosquitoes are most active.
  • Remove sources of standing water in your pasture and around the barn.
  • Use fly masks, fly sheets and/or fly leggings when horses are on pasture.
  • Spray horses with insect repellent.
  • 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
  • Uncoordinated gait, staggering
  • Recumbency, unable to get up
  • Seizures
  • Death  

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

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 Center for Disease Control website. 

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