Media Release

August 12, 2011

York Region reports first positive West Nile virus mosquitoes

NEWMARKET – The Regional Municipality reports three mosquito pools have tested positive for West Nile virus. A pool defines one batch of mosquitoes caught overnight in one trap and sent for testing.

The mosquitoes were trapped in the Town of East Gwillimbury, close to the intersection of Centre Street and Doane Road and in the Town of Markham, close to the intersections of Woodbine Avenue and Highway 407 and John Street and Bayview Avenue.

Ongoing treatment of the catch basins in this area will continue, as well as the necessary treatment of surrounding stagnant water (such as roadside ditches) on public property.

These three positive mosquito pools are the first reported in York Region since 2009. Trapping mosquitoes is part of the 2011 York Region West Nile virus control plan. Traps are set up at various locations throughout the Region, with mosquitoes sent for testing.

The province of Ontario has reported mosquito pools testing positive for West Nile virus are on the rise. Forty-three positive mosquito pools have been found in Ontario to date this year, which is higher than the numbers reported during the same time period for the past four years. Residents should take proper precautions to reduce the risk of contracting the virus.

The symptoms for West Nile virus illness consist of fever, muscle weakness, stiff neck, confusion, severe headache and a sudden sensitivity to light. For a very rare few, the virus causes serious neurological illness, including encephalitis (inflammation of the brain). The risk of being bitten by an infected mosquito and becoming seriously ill as a result of West Nile virus is low.  Approximately four out of five people infected by West Nile virus do not show any symptoms of the illness at all. Those experiencing symptoms should seek medical advice.

Prevention and protection are the best ways to protect yourself and your family from West Nile virus. There are simple and common sense precautions that should be taken:

  • Minimize outdoor activities where and when mosquitoes are most active, such as dusk, night and dawn
  • Wear protective clothing such as long-sleeved shirts, full-length trousers, socks, light coloured clothing and tuck pant legs into socks when possible
  • Apply an insect repellent, as directed
  • Make sure screens on your home are tight-fitting and in good repair

Mosquitoes breed in still water; eliminate stagnant water around your property which may gather in pool covers, flower pots, children’s pools, old tires and birdbaths

The 2011 York Region West Nile virus Control Plan includes:

  • Public education regarding effective measures to prevent exposure to West Nile virus

  • Mosquito and human surveillance
  • West Nile virus control activities, including a larviciding strategy:

    • Four larvicide applications take place over the summer months.  These applications target all catch basins along Regional and municipal roads and in catch basins on private property, as required.
    • Methoprene is the larvicide used.  It comes in a slow-release pellet-like formulation and is administered in catch basins when the mosquito is in the larval stage of development.  It interferes with the mosquito life cycle, preventing the mosquito larva from reaching maturity. The larvicide is not sprayed.  It has been approved by both the provincial and federal governments and is considered low risk for humans, pets and the environment when it is applied according to label directions.
    • Larvicide is applied by licensed Ministry of the Environment applicators.  Treated catch basins are marked with a coloured dot.
    • Residents who are concerned about catch basins on private property are requested to place a mesh screen over the catch basin to prevent mosquitoes from entering and exiting.  Rear-yard catch basins located on private property will be treated by request.
    • In addition, the larvicide Bacillus thuringiensis israelensis (Bti.) and Bacillus sphaericus may be placed in ditches and temporary or permanent standing water pools, including storm water management ponds, if evidence of mosquito breeding is found.  These are naturally occurring bacterium found in the soil.

For more information on West Nile virus or any or public health-related concern, contact York Region Health Connection at 1-800-361-5653 or TTY 1-866-252-9933.

To review the current status of West Nile virus in Ontario, visit


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Samantha Lemieux, Community and Health Services, York Region
1-877-464-9675, ext. 4101 • Cell: 905-716-9753 •

Founded in 1971, The Regional Municipality of York is made up of nine municipalities
and provides services to more than one million residents, 29,000 businesses and 495,000 employees.

 For more information visit us at Follow us on : York Region   @YorkRegionGovt  
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