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West Nile Virus


West Nile Virus (WNV) is a mosquito borne virus that can cause severe illness including encephalitis (swelling of the brain) and can sometimes result in long-term complications and death. The risk of WNV varies from year to year based on precipitation, temperature, mosquito populations and other factors. 


In southern Manitoba, anyone can be exposed to an infected Culex tarsalis mosquito from June to September. The highest risk period occurs when the infected mosquito populations are greatest, typically from mid-July through the end of August. Individuals spending time outdoors at work (e.g. construction, farming etc), or recreationally (e.g. gardening, golfing, at the cottage) are at greater risk of exposure.


While some people who get the virus show no symptoms and do not become ill, others may show mild symptoms such as headache, fever, fatigue and body aches. 

Severe illness has occurred in all age groups. However, severe illness has occurred more commonly in older adults and persons with weakened immune systems. Recovery from these severe symptoms can take months or years. Symptoms include:

  • severe headache; 
  • high fever; 
  • mental confusion; 
  • muscle weakness; 
  • coma; 
  • paralysis. 

See your doctor promptly if you develop any of these symptoms. 


There is no vaccine, cure or specific treatment for West Nile Virus.  Prevention is the first line of defence against the virus.

  • Apply an appropriate insect repellent when outdoors and follow the instructions on the label. 
  • Wear light coloured, loose-fitting clothing with long sleeves and pant legs while outdoors. 
  • Reduce time spent outdoors between dusk and dawn. 
  • Make sure your doors and window screens fit tightly and are free of holes. 
  • Reduce the mosquito habitat around your home by regularly cleaning and emptying water holding containers such as bird baths, wading pools, children's toys, eavestroughs, tarp covers and plant trays. 
  • Ensure that rain barrels are covered with a fine screen and tightly sealed around the downspout. 
  • Clean your yard of old tires, empty flower pots, buckets and any other debris where water collects. 
  • Keep grass mowed and vegetation trimmed around high use areas (e.g. doorways & seating areas). 

As of May 2013, Health Canada has approved the following active ingredients to be safe and effective mosquito repellents: 

  • DEET (no more than 30% strength) 
  • Oil of Lemon Eucalyptus (p-methane-3, 8 diol) 
  • Soybean Oil 
  • Always follow the instructions on the label; application rates may vary by age.

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