Eastern equine encephalitis

Eastern equine encephalitis is a vector-borne disease that can be spread to humans or horses through the bite of an infected mosquito. In the past, eastern equine encephalitis has mainly affected horses; however, in recent years, mosquitoes carrying the eastern equine encephalitis virus have been identified in Ontario.

If someone is infected with eastern equine encephalitis, the person will typically not experience any signs or symptoms. If symptoms do occur, they will often be very general and may include:

• chills
• fever
• muscle pain
• weakness

General symptoms do not involve the nervous system and can last for 2 weeks. Some people infected with eastern equine encephalitis can develop a more severe form of illness called encephalitis (swelling of the brain). This type of illness is rare. If encephalitis develops, symptoms include:

• coma
• drowsiness
• fever
• loss of appetite
• sudden onset of severe headache
• vomiting

About one-third of all patients who develop encephalitis will die from the disease or suffer permanent mental and physical side effects. If you experience any of these symptoms and think you might have eastern equine encephalitis, see your doctor right away.

Whether you are in your backyard, exploring local trails, or vacationing, it’s important to protect yourself and your family from mosquito bites. Here’s how:

• Use an insect repellent to prevent insect bites.
• If possible, stay indoors from dusk to dawn when mosquitoes are most active.
• Wear light-coloured clothing, including long sleeves, long pants, socks, and a hat whenever you are outdoors.
• Check all window and door screens in your home to ensure there are no tears or holes for mosquitoes to get through.

Mosquitoes need only a small amount of calm, standing water to lay their eggs and for larvae to hatch. Change or remove standing water every 2 to 3 days from areas that can hold water, including:

• barrels
• bird baths
• clogged drainage ditches
• clogged gutters and eaves troughs
• flower pot saucers
• old tires
• small containers like cans or bottle tops
• swimming pool covers
• unused children’s toys or vehicles
• unused containers
• wading pools

The transmission cycle (how the virus is passed) begins when mosquitoes feed on the blood of an infected bird. Once a mosquito bites an infected bird, it becomes infected with eastern equine encephalitis and could possibly transmit the virus to humans or horses through a bite.

Eastern equine encephalitis is a virus. There are currently no anti-viral medications available to treat humans infected with eastern equine encephalitis. In Ontario, humans have a very low risk of becoming infected with eastern equine encephalitis.

While there is no treatment for humans, a seasonal vaccination for horses is available. Horses can also be infected and die if they are bitten by a mosquito that is carrying eastern equine encephalitis. By vaccinating horses, these animals will be protected and the hope is, as a result, there will be less spread of eastern equine encephalitis to humans.