The first human case of West Nile virus (WNV) acquired within Canada this year was confirmed just prior to the August long weekend. An adult in Toronto, with no recent travel history, has contracted this mosquito-borne virus. Previously, there had been two reported cases in Canada; however, those individuals had contracted the virus while traveling abroad. This situation highlights the importance of awareness about WNV, especially as people engage in outdoor activities during the summer. Understanding WNV’s origins, transmission, and preventive measures is crucial for public health safety.
West Nile virus was first identified in Uganda’s West Nile region and made its way to various global locations via migratory birds. When mosquitoes feed on infected birds, they can become carriers of the virus and subsequently transmit it to humans and other animals through their bites. Dr. Isaac Bogoch, an infectious disease specialist, notes that the species of mosquitoes responsible for transmitting WNV are most active at dusk and during the night. Human infections typically peak in mid to late summer when temperatures are warmer, although the Public Health Agency of Canada emphasizes that WNV does not spread directly between humans, with only rare transmission cases reported through blood transfusions, organ donations, or from mother to child during pregnancy or breastfeeding.
Symptoms of West Nile virus can vary widely among those infected. A significant number of individuals may not show any symptoms at all, but approximately 20 to 30 percent of those infected will develop some symptoms, typically manifesting between two to 14 days following a mosquito bite. Common symptoms include fever, fatigue, headaches, muscle aches, nausea, vomiting, and in some cases, skin rashes and swollen lymph nodes. However, a small percentage (up to 2%) may develop severe neuroinvasive diseases such as encephalitis or meningitis, which are more likely to affect older adults and can lead to serious complications, including paralysis.
Currently, there is no specific antiviral treatment for West Nile virus. Most affected individuals can manage their symptoms with over-the-counter pain medicine, fluids, and ample rest. For severe cases that result in neuroinvasive diseases, supportive care in a hospital setting is often required. This care may include intravenous fluids and medications to manage neurological symptoms. Due to the lack of a vaccine, prevention remains a critical focus in managing West Nile virus infections.
To prevent West Nile virus, avoiding mosquito bites is paramount. Dr. Bogoch recommends using insect repellents containing DEET or Icaridine, which are effective deterrents against mosquito bites. However, these products are not advisable for infants younger than six months. Parents are encouraged to use mosquito nets over cribs or strollers to protect babies. Additionally, wearing long sleeves, pants, socks, and light-colored clothing can further reduce the likelihood of mosquito bites. Ensuring that windows are screened and eliminating standing water around homes ( where mosquitoes breed) also plays a key role in prevention.
The incidence of West Nile virus fluctuates annually, with reported cases varying widely since the Public Health Agency of Canada began tracking domestic infections in 2003. Reports have ranged from just a handful of cases to a peak of 2,401 in 2007. According to preliminary data for 2024, there have been 166 reported cases, indicating that while WNV is present, the overall risk for most Canadians remains low. This is largely due to the relatively small number of mosquitoes carrying the virus in Canada, emphasizing the importance of continued public awareness and preventive measures as summer progresses.
