Mosquitoes that feed on EEE-infected birds can transmit the virus to humans, horses, and other birds. | Photo: iStock

After the Michigan Department of Agriculture and Rural Development (MDARD) confirmed on Aug. 20 that four horses in three Michigan counties had tested positive for Eastern equine encephalomyelitis (EEE), an additional horse in Barry County tested positive for EEE on Aug. 23.

The unvaccinated 12-year-old Quarter Horse mare presented on Aug. 13 with ataxia (incoordination), fever, head-pressing, and tremors and died from the disease on Aug. 14.

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