August 15, 2005

York Region reports first positive
West Nile Virus mosquitoes

NEWMARKET: York Region Health Services reports that 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 Keele Street and Highway #7. The positive mosquitoes are the first this year in York Region. Surveillance for the virus will be increased in this area.
There was one positive mosquito pool reported last year in York Region and it was found in the Town of East Gwillimbury on August. 4th, 2004. To date in 2005, seven birds have tested positive for WNV in York Region, with two found in the City of Vaughan, three found in the Town of Markham, one in the Town of Newmarket and one in the Town of Richmond Hill. There have been no human cases reported in York Region this season.
Trapping mosquitoes is part of the 2005 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.
• Consider using 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 York Region WNV control plan for 2005 includes:
• Mosquito, bird and human surveillance
• WNV control activities, including a larviciding strategy:
- The strategy includes four larvicide applications (in June, July, August and September). Two larvicide applications have now been completed. These applications target all catch basins along Regional and Municipal Roads and in catch basins, as required, on private property
- Methoprene is the larvicide that is 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
• The WNV control plan also includes public education regarding common sense and effective measures to prevent exposure to WNV

To report a dead crow or blue jay and for more information on WNV or any health-related concern, contact York Region Health Services Health Connection at 1-800-361-5653 or visit
To review the current status of WNV in Ontario, visit

Contact:  Kim Clark, York Region Health Services
   905-830-4444 Ext. 4101

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