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revised Friday February 17 2023

Lyme Disease | West Nile Virus | Eastern Equine Encephalitis

Eastern Equine Encephalitis


Eastern Equine Encephalitis (EEE) at-a-Glance

Eastern equine encephalitis, or EEE:

  • Is a virus normally found in wild birds that can spread to horses and humans through mosquitoes.
  • Is the most severe mosquito-borne disease acquired in North America.
  • Is a rare illness in humans.
  • Can affect the central nervous system and cause severe complications and death.
  • Has been identified in Ontario in horses and mosquitoes, but to date no human cases have been reported.

EEE is a vector-borne disease.

A vector-borne disease spreads to humans or animals through insects called vectors.

Signs and symptoms

Symptoms of EEE usually appear 3 to 10 days after an infected mosquito bites a person.

Most people bitten by an infected mosquito won’t have any symptoms. Others will only get a mild flu-like illness with fever, headache and fatigue.

Severe cases of EEE involves encephalitis (an inflammation of the brain), which starts with a sudden headache, high fever, chills and vomiting. A person with EEE can then become disorientated, suffer seizures and go into a coma. 

Approximately 33% of people who develop EEE encephalitis die of the disease, making it one of the most deadly mosquito-borne diseases in North America. Almost half of those infected survive the illness, but many survivors suffer permanent brain damage.

If you’re experiencing any of these symptoms and think you might have Eastern equine encephalitis, book an appointment with your doctor.

Culiseta melanura
Culiseta melanura the vector of the Eastern equine encephalitis virus in bird populations

Eastern Equine Encephalitis virus (EEEV) is the cause of Eastern equine encephalitis.

Only a few species of mosquitoes spread Eastern equine encephalitis. Mosquitoes become infected by feeding on infected birds. Infected mosquitoes will then occasionally bite and infect horses, people or other mammals.

People and horses infected with Eastern equine encephalitis do not spread the disease.


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Revised: Friday February 17 2023

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