EEE Alert

As of August 20, 2014 there have been four cases of Eastern Equine Encephalitis (EEE) confirmed in Ontario. The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) issued an equine health advisory in response to the death of a horse from EEE on August 9 in Lanark County. Three more cases of EEE, two in Lanark County and one in Frontenac County, were confirmed on August 20.  
“There are cases of EEE that appear in Ontario every year or every other year namely in the northern and/or eastern parts of the province,” Alison Moore, Lead Veterinarian in Animal Health and Welfare with OMAFRA told Ontario Farmer.  “The difficulty is predicting when infected mosquitoes will reach your area of the province.”
The first affected horse, a 12-year old unvaccinated gelding, had no travel history and was euthanized after presenting fever and neurological signs of abnormal eye position and movement, wobbly gait and eventual recumbency. EEE was confirmed on post mortem.
Horse owners should always be concerned about EEE since it is usually fatal in unvaccinated horses, said Moore. Fortunately vaccination can prevent or minimize the signs of disease. She also recommends preventing mosquito exposure by bringing horses indoors during high mosquito time at dawn and dusk, using horse-safe mosquito repellent and eliminating stagnant water.
Moore explained that the ideal time to vaccinate is before the mosquito season starts in the spring but vaccinating now is better than not vaccinating at all. The horse will not be fully vaccinated until a booster vaccine is provided four weeks after the initial shot and most horses will take at least two weeks to develop an antibody response to vaccination depending on the horse’s immune system.
OMAFRA advises veterinarians to consider EEE when presented with neurological signs such as circling, head-pressing, ataxia and depression, which are similar to several other diseases such as rabies, West Nile, botulism, hepatic encephalopathy, equine protozoal myeloencephalitis (EPM) and equine herpes myeloencephalopathy.
Scott Weese, DVM, a member of the steering committee for the Center for Public Health and Zoonoses at the Ontario Veterinary College in Guelph, writes in his Worms and Germs blog, “EEE is a devastating but fortunately rare (around here) disease of horses, people and a few other species. Typically, a few equine cases are identified in Ontario every year, with human cases being rarer. However, since people and horses are infected in the same way, the bite of an infected mosquito, finding the disease in a horse indicates risk to both horses and humans in the region.”
EEE was first detected in the Ontario horse population in 1938. In 2011 there were four EEE cases in horses and an outbreak in pheasants in Ontario. There was one confirmed case in Simcoe County in 2013. Humans can occasionally become infected and the virus can cause fatal infections in pheasants, quail, captive whooping cranes, emus and dogs. Mosquitos are vectors of transmission of the virus with most cases occurring between August and October, coinciding with peak mosquito season.
Ontario’s public health units continue to conduct mosquito surveillance for both EEE and West Nile virus, both naturally hosted in birds and transmissible from infected mosquitos to humans. There have been no positive tests for EEE in mosquitos so far in 2014.
Updates will be posted at
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