West Nile virus spreads in Canada

A dead crow on a Winnipeg street spelled the end to a long running battle against chemical fogging for mosquito control. The crow, found in early July, tested positive for the mysterious West Nile virus.This encephalitis type virus is carried by mosquitoes and spread when they feed on the blood of infected birds. The virus can then be passed on to humans. This summer, there are several confirmed cases of infected birds in southern Ontario and in Manitoba.

^In mid-July, the Manitoba government ordered an end to the 100-metre buffer zone allowance for homeowners who didn’t want their property fogged with the pesticide Malathion. Increasing numbers of requests for no fogging meant entire city neighbourboods went without mosquito control.

And record rainfalls in early summer had supplied the incubator for record numbers of mosquitoes. The infestation was so great, it overwhelmed non-chemical efforts to destroy mosquito larvae. 

Surveillance underway
Reports of dead birds infected with West Nile virus surfaced in North America last summer. The first confirmed Canadian cases occurred in southern Ontario last summer, creati anxiety about the potential impact on people.

So Health Canada and provincial health departments set up a surveillance system to test dead birds for the virus. Members of the crow family, such as magpies, blue jays and ravens, are most susceptible to the virus.

People have been asked to report any findings of dead birds to health authorities.

Those at risk
In most cases, healthy people can ride out West Nile virus. They may not even show symptoms, which include muscle aches, fever and joint pain. The greatest risk is to those with weakened immune systems.

“The very young and the elderly,” says Dr. Brian Aw, family physician and travel medicine specialist in Toronto, “they’re more susceptible to fatal complications such as encephalitis, which is a swelling of the brain.”

Exposure to the virus can only be detected through a blood test and there is no vaccine or pill to prevent or cure the virus in humans.

“Because there is no prevention, it’s all about protection—protecting yourself from insects,” says Aw.

Next page: Protection best prevention

Protection best prevention
The best method of prevention is regular use of repellants, in particular, those that contain the ingredient DEET. For those who prefer to go the green route, there are many natural-based products such as citronella-based Natrapel.Other protective measures:

  • Put your repellent on before you arrive at the cottage (all it takes is one bite)
  • Avoid wearing dark colours, which attract mosquitoes
  • Avoid using hair spray and perfume
  • Stay indoors during mosquito prime time (the hours between dusk and dawn).

For more information, see Health Canada’s West Nile Virus Surveillance website. 

With files from Marilyn Smith and Jennifer Walker.