Ottawa Public Health cautioning residents after mosquito-borne illnesses found in human, horse in Ottawa

Mosquitoes cling to the inside of a jar loaded with repellent during a test as part of a tour of the Center for Disease Control laboratory in Fort Collins, Colo., on April 4, 2024. (AP Photo/David Zalubowski, File)

Ottawa Public Health (OPH) is recommending residents be vigilant and protect themselves against mosquitoes after confirming a case of West Nile virus in a human in the city and a case of eastern equine encephalitis virus (EEEV) in a horse.

OPH recently confirmed the presence of West Nile virus in local mosquitoes earlier this month.

No other details about the human case have been released. This is the first human case of West Nile virus confirmed in Ottawa this year.

Both West Nile virus and EEEV can spread to humans through mosquito bites. OPH says anyone who lives, works, or participates in outdoor activities where mosquitoes are present can be at risk.

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“Protecting yourself from mosquito bites is the best way to prevent WNV and EEEV,” OPH said in a news release on Wednesday.

Methods to protect yourself against mosquito bites include:

• 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

OPH says there have been 11 human cases of West Nile virus in Ontario so far this year. In 2024, there were 13 human cases of West Nile virus in Ottawa and 87 in Ontario.

“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,” OPH said.

Symptoms of West Nile virus include fever, headache, muscle aches, and 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,” OPH said.

EEEV typically spreads between wild birds and mosquitoes but can affect horses and, rarely, humans, by being bitten by an infected mosquito. The disease does not transmit from horses to humans or from human to human, OPH says.

“Although rare, the disease is of concern because, like WNV, it can cause a serious neurological disease and even death,” OPH said.

One Ottawa resident who died last year of a viral encephalitis tested positive for an EEEV infection.

The health unit says mosquitoes that carry West Nile virus are most commonly found around homes in urbanized areas, but the mosquitoes that carry EEEV are usually found close to swampy hardwood forests.

Eliminating standing water around your home is one of the ways you can help prevent mosquitoes from breeding. Some tips include:

• Look around and outside your house for containers, receptacles and any other items that might collect water. Be sure to empty them regularly, turn them over when appropriate, or dispose of them accordingly.
• Drill holes in the bottom of recycling containers that are left outdoors so that water can drain out.
• Clean clogged roof gutters; remove leaves and debris that may prevent drainage of rainwater.
• Ensure all openings to rain barrels are covered with screen mesh at all times.
• Turn over plastic wading pools and wheelbarrows when not in use.
• Change the water in birdbaths at least once per week; aerate private ornamental ponds or treat them with an approved mosquito larvicide such as Bti if they do not have an outflow into natural waters.
• Keep swimming pools clean and properly chlorinated; remove standing water from pool covers.
• Use landscaping to eliminate standing water that collects on your property.