MDARD Confirms First Cases of Eastern Equine Encephalitis and West Nile Virus for 2023 in Horses

For immediate release: September 11, 2023
Media contacts: Jennifer Holton, 517-284-5724 or Chelsea Lewis-Parisio, 517-331-1151

LANSING, MI—The Michigan Department of Agriculture and Rural Development (MDARD) is reporting Michigan’s first cases of Eastern equine encephalitis (EEE) and West Nile virus (WNV) in domestic animals. EEE was detected in a seven-year-old Standardbred gelding from Mecosta County, and the WNV case occurred in a four-month-old Belgian colt from Calhoun County. Both horses were unvaccinated against their respective diseases. These detections highlight the importance for Michiganders to continue taking precautions to protect their animals and themselves from mosquito bites.

“While these are the first confirmed cases of EEE and WNV in domestic animals for 2023, these viruses were already found in mosquito pools and wild birds throughout 14 Michigan counties this season,” said State Veterinarian Dr. Nora Wineland. “These detections indicate these diseases are present and circulating within the state’s mosquito population, so protecting animals from being exposed to these insects is crucial. Preventing mosquito bites will prevent mosquito-borne diseases.”

EEE and WNV are both viral diseases transmitted through the bites of mosquitoes to both animals and people; they are typically seen in late summer to early fall each year in Michigan. These diseases are not spread by horse-to-horse or horse-to-human contact.

“These discoveries are a reminder that the EEE virus is here in Michigan and provides warning that people can also become infected by a mosquito,” said Dr. Natasha Bagdasarian, MDHHS chief medical executive. “Michigan residents are urged to take precautions and protect themselves from mosquito bites as EEE is one of the most dangerous mosquito-borne diseases in the U.S., with a 33 percent fatality rate among people who become ill.”

So far this year, EEE was detected in four mosquito pools from Bay, Barry, and Saginaw counties, and WNV was detected in 98 mosquito pools from Bay, Genesee, Iosco, Kalamazoo, Kent, Oakland, Saginaw, Tuscola, Washtenaw, and Wayne counties. There have also been four human cases of WNV and four cases of WNV in wild birds. Fortunately, there are no additional detections of EEE in humans or animals.

Despite the cooler temperatures being experienced around the state, the mosquitoes that carry EEE and WNV will remain alive and active until there has been at least one hard freeze where the temperatures fall below 28 degrees Fahrenheit.

To prevent the occurrence of these viruses in horses and other animals, owners can:

  • Talk to a veterinarian about vaccinating horses against EEE, WNV, and other mosquito-borne diseases.
  • Eliminate standing water—i.e., fill in puddles, repair eaves, and change the water in buckets and bowls at least once a day.
  • Place livestock in a barn under fans (as mosquitoes are not strong flyers) and pets inside the home during peak mosquito activity from dusk to dawn.
  • Use an insect repellant on animals that is approved for the species.
  • Contact a veterinarian if an animal shows signs of illness.

Residents can stay healthy by using simple, effective strategies to protect themselves and their families. The following steps are recommended to avoid mosquito-borne diseases:

  • Apply insect repellents that contain the active ingredient DEET or other EPA-approved products to exposed skin or clothing. Always follow the manufacturer’s directions for use.
  • Wear long-sleeved shirts and long pants when outdoors. Apply insect repellent to clothing to help prevent bites.
  • Maintain window and door screening to help keep mosquitos outside.
  • Empty water from mosquito breeding sites around the home, such as buckets, unused kiddie pools, old tires and other water-holding containers where mosquitos can lay eggs.

Please also note that EEE and other mosquito-borne diseases are reportable to MDARD. Cases can be reported by completing and submitting a Reportable Disease Form to

If a Michigan animal is suspected of having WNV or EEE, funding is available under an arbovirus grant to cover these testing costs. Please contact MDARD at 800-292-3939 for more details.

For more information about EEE and WNV, please visit


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