Mosquito-Borne Illnesses Appear In Ottawa
Ottawa Public Health (OPH) is recommending that residents protect themselves against mosquito bites to reduce the risk from West Nile virus (WNV) and Eastern Equine Encephalitis virus (EEEV).
Ottawa Public Health is reporting the first human case of WNV infection in an Ottawa resident for the 2025 season and has confirmed that a horse in Ottawa recently tested positive for EEEV.
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This is a release from the City of Ottawa.
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Both diseases spread to humans through mosquito bites and anyone who lives, works, or participates in outdoor activities where mosquitoes are present can be at risk. Protecting yourself from mosquito bites is the best way to prevent WNV and EEEV.
Ottawa Public Health urges residents to protect themselves and their families from mosquito bites when spending time outside at home or in the woods by:
Applying a Health Canada-approved mosquito repellent containing DEET or icaridin to exposed skin and clothing
Wearing light-coloured, tightly woven, loose-fitting clothing, such as long pants, a long-sleeved shirt, shoes and socks, to protect exposed skin
Making sure all windows and doors in your home have screens that are in good condition
Removing, or emptying once per week, standing-water sites around your home, such as bird baths, toys, flower-pot saucers, swimming-pool covers, old tires, wheelbarrows, buckets, and cans
Keeping all openings to rain barrels covered
West Nile virus is an infection spread primarily by the northern house mosquito (Culex pipiens) that, in a small number of cases, can cause serious illness. Most people will not develop any symptoms if infected, but about 20 per cent may experience flu-like symptoms, such as:
Fever
Headache
Muscle aches
Rash
The risk of more serious illness – occurring in less than one per cent of infections, in which WNV impacts the central nervous system – increases with age. Older adults, the elderly and people with weakened immune systems are at higher risk.
In Ontario, as of August 20, 2025 (including data up to August 17), there have been 11 human cases of WNV. In 2024, there were 13 human cases of WNV in Ottawa and 87 in Ontario.
Eastern Equine Encephalitis virus is normally transmitted between wild birds and mosquitoes but can occasionally infect horses and, rarely, humans through infected mosquitoes’ bites, similar to the transmission of WNV. Humans do not get infected from a horse or another human. Whereas mosquitoes that carry WNV are most commonly found around homes in urbanized areas, the mosquitoes that carry EEEV are usually found close to swampy hardwood forests.
Human infections with EEEV have been rare in Ontario. Historically, there have been four human cases of EEEV in Ontario, the most recent reported in 2024 in Ottawa. Although rare, the disease is of concern because, like WNV, it can cause a serious neurological disease and even death.
Visit OttawaPublicHealth.ca/WestNileVirus to learn more about mosquito-borne diseases. Residents can also connect with OPH on Facebook, Instagram, Bluesky and YouTube.
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Does Ottawa have a mosquito spraying program and if not why not? I remember way back in the day in Playfair Park the spraying program. I didn’t hear or see anyone collapsing and as a kid the result was no skitters which meant lots of outside play!
There’s a program in Kanata which puts a bioside into water of local ponds and streams. The interesting thing is the type of mosquito has changed. So as they eradicate one type of mosquito, another one pops up. And this has been happening now for about 5 years. Last year the mosquitoes that were after us were very quick and very painful. This year we don’t seem to have as many mosquitoes but we have a little black fly that doesn’t hurt a lot when it bites you but it swells you up at the point where your bit to the size of a toonie. I’m reminded of that comment in Jurassic park that nature finds a way.
And by the way it’s pretty useless to put out that warning without at least saying what part of Ottawa they’re finding these mosquitoes
Mr Davies. The grass on median strips between lanes of traffic moving in opposite directions used to be covered with grass which has been replaced primarily by dandelions and other weeds since the province decided that halting the use of herbicides to keep weeds at bay was in everyone’s best interest healthwise. I don’t know how old but obviously you’re still alive and flourishing and would have been so herbicides or not.