Two Michigan Horses Euthanized Due to EEE

The horses were from different counties. One was unvaccinated for EEE; one’s vaccination status is unknown.

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Michigan, Livingston County
A 14-year-old mare from Livingston County was confirmed positive on Sept. 27 and was euthanized. | Photo: Wikimedia Commons
Officials at the Michigan Department of Agriculture and Rural Development (MDARD) have confirmed that two horses in separate counties were euthanized due to Eastern equine encephalomyelitis (EEE). The first horse, a yearling Quarter Horse colt that resided in Otsego County, began showing clinical signs consistent with EEE on Sept. 24. Signs consisted of fever, muscle fasciculations (twitching), ataxia (incoordination) and recumbency (down and unable to rise). He was unvaccinated against EEE and was euthanized due to the severity of his signs.

The second horse, a 14-year-old Thoroughbred mare from Livingston County with unknown vaccination status, began showing signs on Sept. 26. Signs included fever, ataxia, and walking in circles. She was confirmed positive on Sept. 27 and was also euthanized.

EEE 101

Eastern equine encephalomyelitis is caused by the Eastern equine encephalitis virus, for which wild birds are a natural reservoir. Mosquitoes that feed on EEE-infected birds can transmit the virus to humans, horses, and other birds. Horses do not develop high enough levels of these viruses in their blood to be contagious to other animals or humans. Because of the high mortality rate in horses and humans, EEE is regarded as one of the most serious mosquito-borne diseases in the United States.

Health Alert: EEE, WEE, and VEE
VIDEO | Health Alert: EEE, WEE, and VEE

Tips for preventing mosquito-borne diseases include:

  • Avoid mosquito bites: Use insect repellent when outdoors, especially from dusk to dawn.
  • Look for EPA-labeled products containing active ingredients such as DEET, picaridin (KBR3023), or oil of lemon eucalyptus (p-menthane 3,8-diol).
  • Apply more repellent, according to label instructions, if mosquitoes start to bite.
  • Mosquito-proof homes: Fix or install window and door screens, and cover or eliminate empty containers with standing water where mosquitoes can lay eggs.
  • Protect your horses: Veterinarians recommend commercially available licensed vaccines against EEE for all horses in the U.S. Horses should be vaccinated at least annually (recommendations vary in high-risk areas). It’s not too late this year to vaccinate your horses.
  • Use approved insect repellents to protect horses.
  • If possible, put horses in stables, stalls, or barns during the prime mosquito exposure hours of dusk and dawn.
  • Eliminate standing water, drain water troughs, and empty buckets at least weekly.
  • Stock water tanks with fish that consume mosquito larvae (contact your local mosquito control for assistance), or use mosquito “dunks” (solid “donuts” of Bacillus thuringiensis israelensis, which are nontoxic to horses) available at hardware stores.


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