Health Department begins 2021 West Nile virus surveillance activities

Whitby, Ontario - Durham Region Health Department has started West Nile virus (WNV) surveillance and control activities for the 2021 season. Ongoing surveillance for WNV involves a number of activities to monitor for the virus across the Region including, implementing a weekly adult mosquito-trapping program, a larval mosquito surveillance program and a larviciding program involving regional catch basins, as well as identifying stagnant water sites where mosquitoes could breed.

West Nile virus is a mosquito-borne disease that is spread to humans through the bite of an infected mosquito. Mosquitoes become infected by feeding on the blood of birds that carry the virus. The disease is not passed from person to person or from bird to person. Since 2001, WNV has been found in birds, mosquitoes, horses and humans in Ontario. For 2020, the Public Health Agency of Canada reported 77 human cases of the virus in Ontario, compared to 19 human cases in 2019. Durham Region had seven confirmed human cases and six probable human cases of the virus in 2020.

The Health Department also routinely traps batches of adult mosquitoes which are then tested for the virus. In 2020, 10 positive mosquito batches trapped by the Health Department tested positive for WNV, which is an increase from 2019 when just one batch of mosquitoes tested positive. In addition to testing adult mosquitoes for the virus, the Health Department also uses indicators such as larval mosquito surveillance to determine the risk of the virus for area residents.

Area residents are advised to remove or cover any standing water around their homes to help reduce or eliminate the opportunity for mosquitoes to lay eggs that develop into larvae and, ultimately, become mosquitoes which can spread the virus.

The Health Department recommends the following specific steps to help minimize potential breeding sites for mosquitoes:

• Chlorinate rain barrels or cover them with mosquito screening.
• Drain water from areas such as pools and chair covers, and from containers such as ceramic pots, wading pools, bird baths, planters, etc.
• Check that roof gutters are cleared and draining properly.
• Clean and properly maintain swimming pools and outdoor hot tubs.
• Remove all unused tires from your property.
• Ensure that drainage ditches are not backed up and holding stagnant water.

To help reduce the possibility of being exposed to WNV, residents are encouraged to take the following precautions:

• Wear shoes, socks and light-coloured clothing with long sleeves and full-length pants when outside, especially overnight, between dusk and dawn, when mosquitoes are most active.
• Use insect repellent containing DEET on exposed skin, following Health Canada’s safety tips on using personal insect repellents. More information on using insect repellents containing DEET can be found at www.canada.ca/en/health-canada/services/about-pesticides/insect-repellents.html?_ga=1.190416748.61038264.1464190033.
• Ensure doors and windows have screens that are tight-fitting and in good repair.
• Keep grass, shrubs and hedges trimmed.
• Turn over compost piles regularly.

For more information about West Nile virus and the Health Department’s surveillance activities, please call Durham Health Connection Line at 905-668-2020 or 1-800-841-2729, or visit durham.ca/WestNile.

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For more information, please contact the Health Department