September 1, 2009
Media Release

York Region reports first positive West Nile virus mosquitoes

NEWMARKET … The Regional Municipality of York Community and Health Services department reports a mosquito pool has tested positive for West Nile virus (WNV).  A pool defines one batch of mosquitoes caught overnight in one trap and sent for testing.
The mosquitoes were trapped in the City of Vaughan, close to the intersection of Highway 27 and Major Mackenzie Drive West.  The positive mosquitoes are the first this year in York Region.  On-going 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.
In 2008, there were two positive mosquito pools reported in York Region.  To date this year, there have been no positive cases of human WNV in York Region.
Trapping mosquitoes is part of the 2009 York Region WNV control plan. Traps are set up at various locations throughout the Region, with mosquitoes sent for testing.
The symptoms for WNV 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).  Those experiencing symptoms should seek medical advice.
Prevention and protection are the best ways to protect yourself and your family from WNV.  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 2009 York Region West Nile virus (WNV) Control Plan includes:
• Public education regarding effective measures to prevent exposure to WNV
• Mosquito and human surveillance
• WNV 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.  It 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 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 WNV or any health-related concern, contact York Region Health Connection
at 1-800-361-5653.
To review the current status of WNV in Ontario, visit
For more information on The Regional Municipality of York, please visit
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Media Contact: Jennifer Mitchell-Emmerson, York Region Health Services
 Phone:  (905) 830-4444, ext. 4016 or After-hours Cell:  905 716-9753


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