The Michigan Department of Agriculture and Rural Development (MDARD) confirmed on Aug. 9 that a 19-year-old Standardbred mare presented with clinical signs (high fever, down and unable to get up) of Eastern equine encephalomyelitis (EEE) on Aug. 4 and was euthanized after becoming unable to rise. The mare had not been vaccinated against the disease.

Eastern equine encephalomyelitis is caused by viruses found in wild birds. Mosquitoes that feed on birds infected with EEE can transmit the disease to humans, horses, and other birds. Some birds can harbor the EEE virus without becoming acutely ill, thereby serving as reservoirs for the disease. 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 for horses and humans, EEE is regarded as one of the most serious mosquito-borne diseases in the United States.

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