EEE Confirmed in Eastern Ontario Horse

EEE Confirmed in Eastern Ontario Horse

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes.


An advisory from the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) indicates that the agency received notification Aug. 9 that a horse residing in the United Counties of Stormont, Dundas, and Glengarry, Ontario Canada, tested positive for Eastern equine encephalitis (EEE).

"The 12-year old unvaccinated gelding with no travel history was euthanized following the sudden onset and progression of fever and neurological signs," the advisory said. "The horse presented with signs of nystagmus and strabismus (abnormal eye position and movement) along with ataxia (wobbly gait) and eventual recumbency. A post-mortem examination was performed at the Animal Health Laboratory in Kemptville, Ontario and EEE was confirmed by testing of brain tissue."

The advisory indicates that EEE has been present in Ontario's horse population since 1938, and that one case was confirmed last year.

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.

Health Alert: EEE, WEE, VEE

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.

Vaccinating horses against EEE coupled with mosquito control are the most important ways to minimize an animal's chances of becoming infected. In the northern regions of the United States, most veterinarians recommend vaccinating horses in the spring prior to peak mosquito levels. In the south, where mosquito populations are present year-round, veterinarians might recommend more frequent vaccination.

Minimizing mosquito populations near your horses by eliminating mosquito breeding and resting areas will reduce the chances these insects bite and infect horses and the people who care for them.

For example, reduce or eliminate sources of stagnant or standing water, remove muck from areas near the horses, stable horses during peak mosquito periods (i.e., dawn and dusk), use equine-approved mosquito repellants, place fans inside barns or stalls to maintain air movement, keep weeds and grass trimmed, and avoid using incandescent bulbs inside stables at night. Instead, place incandescent bulbs away from the stables to attract mosquitoes to areas away from horses.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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