On July 23, the Wisconsin Department of Agriculture, Trade, and Consumer Protection, confirmed the July 21 euthanasia of a 10-year-old mare in the state that had contracted Eastern equine encephalomyelitis (EEE). The mare, located in Dunn County, first exhibited clinical signs of neurologic disease on July 13. She had not been vaccinated against EEE. This is the first confirmed EEE case in Wisconsin for 2020.

A second horse—a weanling aged 4 or 5 months—was suspected to have EEE after it began circling and became recumbent. The foal 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