TORONTO – The Public Health Agency of Canada confirmed the first human case of West Nile virus acquired within the country for the year, just ahead of the August long weekend. An adult in Toronto, who has no travel history, was found to be infected with the mosquito-borne virus. Prior to this case, two individuals were reported with West Nile virus, but their infections occurred while traveling outside Canada.
What is West Nile Virus?
West Nile virus was first detected in humans in Canada in 2002. Initially identified in the West Nile region of Uganda, the virus has spread globally through migratory birds. When mosquitoes bite infected birds, they become carriers of the virus and can transmit it to humans and other animals via their bites. According to Dr. Isaac Bogoch, an infectious diseases specialist at the University Health Network in Toronto, the mosquitoes that transmit West Nile virus typically feed during dusk and nighttime. Human infections are most common in mid to late summer and decline as temperatures drop.
The Public Health Agency of Canada has indicated that humans do not spread the virus among themselves, with only rare exceptions occurring during blood transfusions, organ or tissue transplants, or mother-to-child transmission during pregnancy or breastfeeding.
What Are the Symptoms?
Dr. Bogoch notes that the majority of individuals bitten by mosquitoes carrying West Nile virus exhibit no symptoms. For the estimated 20 to 30 percent who do become ill, symptoms are generally mild and resolve independently. Symptoms typically manifest between two and 14 days after a mosquito bite and may include fever, muscle aches, headaches, fatigue, nausea, vomiting, skin rash, swollen lymph glands, and stiff neck. Notably, up to two percent of infected individuals may develop neuroinvasive diseases, such as encephalitis or meningitis. Encephalitis results in inflammation of the brain, while meningitis pertains to inflammation around the brain and spinal cord. In rare instances, paralysis can occur, with severe infections being more prevalent in older adults.
How is West Nile Virus Treated?
Currently, there is no antiviral medication specifically for treating West Nile virus. Most afflicted individuals can manage their symptoms with over-the-counter acetaminophen, rest, and hydration. For cases of neuroinvasive diseases, hospitals will provide supportive care, which includes administering fluids and electrolytes, and rehabilitation as necessary.
Is There a Vaccine for West Nile Virus?
There is no available vaccine for West Nile virus.
How Can I Prevent West Nile Virus?
The most effective strategy to prevent West Nile virus infection is to avoid mosquito bites. Dr. Bogoch emphasizes the effectiveness of insect repellent, recommending products containing DEET or Icaridine. Both he and the Public Health Agency of Canada urge caution for infants under six months, suggesting parents use mosquito nets over cribs or strollers. Wearing long sleeves, long pants, socks, and hats can also provide a level of protection against bites. Light-colored clothing is advised, as mosquitoes are attracted to darker hues.
Ensuring that windows have screens to keep mosquitoes out is critical, as is eliminating standing water around homes or cottages, where mosquitoes lay their eggs. Draining buckets, planters, old tires, pool covers, and other water-accumulating items will help reduce mosquito breeding spots.
How Common is It?
The annual number of reported West Nile virus cases in Canada varies significantly, with the Public Health Agency of Canada beginning to monitor domestic infections in 2003. Reports have ranged from a few cases to a peak of 2,401 during 2007. According to preliminary data, 166 cases were reported in 2024. Mark Johnson, a spokesperson for PHAC, stated in an email that the likelihood of Canadians contracting the virus is generally low, given that relatively few mosquitoes in Canada carry West Nile virus.
