Mosquitoes in Toronto have tested positive for West Nile Virus. Here’s what you need to know to protect yourself

Infectious diseases expert Dr. Isaac Bogoch on what you need to know about West Nile, Rocky Mountain spotted fever and the Measles.

West Nile is back in the headlines, with mosquitoes testing positive for the virus in Toronto, Niagara Region and York Region in the last week.

While there haven’t been any confirmed cases in humans in Ontario so far this year, there are a few crucial things to know about the virus and how to protect yourself from it.

What is the West Nile virus?

West Nile is a mosquito-borne virus that has the potential to cause fatal neurological disease. It is transmitted to humans through mosquitoes.

Mosquitoes initially catch West Nile by feeding on perching birds, like robins, that habour the virus, creating a cycle, explained Dr. Robyn Klein, a professor at Schulich Medicine & Dentistry whose focus is on neurovirology and neuroimmunology.

“They are passing the virus between mosquitoes and birds and that’s how it’s maintained in nature,” she said.

Some birds, like crows, are more susceptible to West Nile and can be killed by the virus. If there are several dead crows in an area, it`s often a sign that the virus is nearby.

What does the West Nile virus do?

Most people infected with the virus are asymptomatic, which means they don’t feel anything and don`t exhibit any symptoms.

Mild symptoms can include fever, headache, body aches, mild rash and swollen lymph glands. People who are 50 years old or older, have underlying conditions or a weaker immune system are at risk for more severe symptoms.

Those include a quick onset of severe headache, high fever, stiff neck, nausea and/or vomiting, trouble swallowing, drowsiness, confusion, loss of consciousness, lack of co-ordination, muscle weakness or paralysis.

Initial symptoms generally appear within two to 15 days after infection.

For mild cases, recovery can take a week, while more severe cases have the potential to result in a slew of health issues that can last months or years after initially contacting the virus.

According to Health Canada, less than one per cent of infected patients will develop severe symptoms that affect the central nervous system.

Those infected with the virus cannot spread it to other humans. There is no vaccine for West Nile or medication for those infected.

Klien said if someone is concerned about whether they have the virus, they can get an antibodies test through their health care provider, though it’s not usually necessary for mild cases.

“If you have a neuroinvasive form of the disease, generally people will need to have a spinal tap to obtain spinal fluid to test for antibodies,” she said.

How to protect yourself?

Mosquitos breed in standing water, so be sure to check for areas around your home where water can collect, particularly after a rainfall. These include bird baths, flower pots, pool covers, eavestroughs and gutters.

Mosquitos are most active at dusk, night and dawn. If you’re planning to spend time outside during these times, it’s advised that you cover up with long sleeved shirts and pants in light colours, as mosquitos are attracted to darker colours.

It’s also advised to use insect repellent that contains DEET on exposed skin and clothing.

Make sure the windows and doors in your home have screens in good condition.

What is the city doing?

Toronto Public Health runs weekly mosquito surveillance from mid-June until mid-September every year. Twenty-two mosquito traps are set across the city to collect mosquitos for identification and West Nile virus testing.

Confirmed and suspected human cases of the illness for Toronto residents are reportable to Toronto’s Medical Officer of Health and are investigated by Toronto Public Health.

Bulletins are posted to update medical professionals and the public health community with thorough epidemiologic information on the West Nile virus in Toronto. Reports are posted if sufficient cases need to be reported.

How many cases of West Nile are reported in Canada?

According to the most recent data from Public Health Ontario, there were 61 cases in 2023, resulting in 37 hospitalizations and one death.

Toronto Public Health says that in 2023, there were a total of 22 human cases in the city.

The highest number of cases in Ontario in the last decade was in 2017 when there were a total of 159 incidents of West Nile Virus.