The North Bay Parry Sound District Health Unit has reported that a dead horse in the Sundridge, Ontario, Canada, area tested positive for Eastern equine encephalitis (EEE).

There has never been a human case of EEE reported in Ontario or Canada, although it has been identified previously in horses and mosquitoes. Horses or people infected with EEE cannot spread the disease.

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. Clinical signs of EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems.

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Horse owners should also consult their private practicing veterinarian to determine an appropriate disease prevention plan for their horses. Vaccines have proven to be a very effective prevention tool. Horses that have been vaccinated in past years will need an annual booster shot. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three to six week period.

In addition to vaccinations, horse owners