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

On Sept. 8, Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) officials confirmed a horse in the united counties of Leeds and Grenville, Ontario, with Eastern equine encephalomyelitis (EEE). The affected 8-year-old gelding of unknown breed experienced onset of clinical signs on Aug. 26. Signs included fever and ataxia (loss of muscle control). He was unvaccinated and is reported as recovering.

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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