The West Nile Virus and the landscape industry

In 2002, North America experienced an unprecedented outbreak of illness, including encephalitis and meningitis, caused by West Nile Virus. West Nile Virus (WNV) is a virus found in wild birds and carried by mosquitoes (in Ontario several mosquito species spread WNV including Culex pipiens, Culex restuans and Ades vexans). It was first identified in the province of West Nile, Uganda in 1937. Since then it has been identified in Egypt, Asia, Israel, South Africa, parts of Europe and Australia. It was present in the United States for the first time in 1999. The presence of WNV in Canada was confirmed on August 22, 2001 when a bird was submitted from Windsor-Essex Country. In the summer and fall of 2002, birds tested positive for WNV in 39 regions across Ontario.


WNV affects wild birds, mainly crows and blue jays, and can be transmitted to humans through mosquito bites. Although the risk of disease in humans is low, Health Canada reports 305 confirmed cases of WNV in Ontario in 2002, with 17 deaths. Those most at risk of severe illness and death are the elderly. Of those infected, 80 per cent have no symptoms, almost 20 per cent have West Nile fever, consisting of fever, headache, muscle ache, and rash. For every case of serious disease, 150 more people are thought to be mildly infected, with either a flu-like illness or, in most cases, no symptoms at all.


There is no treatment, just supportive care. A vaccine for people will require years more research, although there is one for horses – also hard-hit by West Nile – and some zoos are testing one for endangered birds. Once infected, symptoms or not, you’re thought to be immune for life. So eventually, West Nile epidemics should become rare.





What can I do to reduce my risk of becoming infected with West Nile Virus?


Personal Protection

The best way to prevent yourself from getting infected with West Nile virus is by protecting yourself from mosquito bites. This is particularly critical for the horticulture industry, as most workers spend much of their day outdoors. Mosquitoes are most active from dusk to dawn, but all outdoor workers should take the following precautions to reduce their risk of being bitten:



  • Avoid areas with large numbers of mosquitoes.

    Wear light-coloured clothing, including long sleeves, long pants and a hat whenever you are outdoors.
  • Spray clothing with mosquito repellents containing 30 per cent DEET or less to ward off mosquitoes that may bite through thin clothing.
  • Apply repellent sparing to exposed skins and follow the manufacturer’s direction for use.
  • Choose the correct DEET containing product suitable for the age of the person and for the time spent outdoors. Insect repellents that contain 30 per cent DEET will remain effective for approximately five hours, 10 per cent DEET will provide approximately three hours of protection, while five per cent DEET provides approximately two hours.
  • Children should wear a mosquito repellent with a six to 10 per cent DEET concentration.
  • Check all window and door screens in your home for tears or holes.




Alternative to DEET insect repellents


The Pest Management Regulatory Agency is currently re-evaluating citronella and lavender oil. Please follow the label information regarding general use.


It is recommended that these products not be used on children under two years of age.


The citronella oil registered in Canada to protect people against mosquito bites can last for less than one hour. The registered lavender oil provides protection for half-an-hour or less
Based on animal studies, citronella-based products can cause allergic reactions to some individuals.


Note: Outdoor repellents such as citronella candles and mosquito coils are not entirely effective at protecting against mosquitoes. They must be used under proper conditions. The area needs to be protected so there is little breeze to dissipate the ingredients
Ultrasonic devices, incense, and bug zappers have not been shown to be effective in preventing mosquito bites. The purpose of these devices is to attract mosquitoes. Therefore, if you wish to use one, ensure that it is located away from the home or deck.



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