Reminder to protect against mosquitos following more positive cases of eastern equine encephalitis (EEEV)

Published on
September 20, 2023
Health, public safety and emergencies
Home and community

Ottawa Public Health (OPH) previously announced that a horse in the Ottawa area had tested positive for eastern equine encephalitis virus (EEEV). Since then, several other Ottawa-area horses have been identified to have developed the disease. OPH continues to encourage residents to take precautions against mosquito bites to protect themselves against EEEV as well as West Nile virus (WNV). Risk of these mosquito-borne diseases is ongoing until we have had several hard frosts.

Like WNV, EEEV normally cycles between wild birds and mosquitoes but can occasionally be spread to horses and, rarely, to humans through an infected mosquito’s bite. Humans do not get infected with EEEV from a horse or another human. The mosquitoes that carry EEEV are usually found close to swampy, flood-prone woods, while WNV-carrying mosquitoes favour urban and suburban environments.

Over the years, there have been three human cases of EEEV in Ontario. Although rare, the disease is of concern because it can cause serious neurological disease and even death.

Although horses can be protected by a vaccine against EEEV, there is no vaccine for humans. Persons can take the following steps to protect themselves from mosquito bites:

  • Apply insect repellent containing DEET or icaridin, making sure to follow label directions; 
  • Wear light-coloured, loose-fitting, tightly-woven clothing with long sleeves, long pants and socks; 
  • Avoid being outside from dusk to dawn when mosquitoes are most active, and anytime in shady, wooded areas; 
  • Ensure that window and door screens are well fitting and without holes. 

To reduce mosquitoes around your home, ensure that all containers in or around your property such as tires, pool covers, bird baths, rain barrels, recycling/garbage bins, saucers for flowerpots, wading pools and children’s toys are removed or emptied of standing water at least once per week. Ornamental ponds should have strongly circulating water or be treated with a mosquito larvicide.

Horse owners are reminded that the best protection against EEEV is vaccination of their animals. Owners should contact their veterinarian for advice and support.

For more information about EEEV, please visit To learn more about other mosquito-borne viruses, visit Ottawa Public Health, call 613-580-6744 or call 3-1-1 after hours.

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