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Region begins West Nile virus surveillance activities


The region’s health department has started West Nile virus surveillance and control activities for the 2019 season.

WNV 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.

As part of its ongoing WNV surveillance activities, the health department routinely traps batches of adult mosquitoes, known as mosquito pools, which are then tested for the virus.

In 2018, seven of the mosquito pools trapped by the health department tested positive for the virus. This represents a decrease from 10 positive mosquito pools in 2017.

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 WNV for area residents.

“Mosquitoes lay their eggs in standing water, these eggs then become mosquito larvae,” explains Ross MacEachern, manager of health protection with the health department. “Therefore, area residents are reminded to remove or cover any standing water around their homes to help reduce the development of mosquito larvae.”

Since 2001, WNV has been found in birds, mosquitoes, horses and humans in Ontario.

For 2018, the Public Health Agency of Canada reported 126 human cases of the virus in Ontario, compared to 155 human cases in 2017.

Durham Region had five confirmed human cases of WNV in 2018, compared to three human cases in 2017.

The health department has recommended residents take specific steps to help minimize potential breeding sites for mosquitoes.

These include chlorinating rain barrels or covering them with mosquito screening, draining water from areas such as pools and chair covers, and from containers such as ceramic pots, wading pools, bird baths, and planters.

The health department also recommends residents check that roof gutters are cleared and draining properly, and to clean and properly maintain swimming pools and outdoor hot tubs.

It is also recommended residents remove all unused tires from their property and ensure that drainage ditches are not backed up.

To help reduce the possibility of being exposed to the virus, residents are encouraged to take some precautions.

These include wearing 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.

Residents are also encouraged to use insect repellent containing DEET on exposed skin, following Health Canada’s safety tips on using personal insect repellents.

Residents should also ensure doors and windows have screens that are tight-fitting and in good repair, keep grass, shrubs and hedges trimmed, and turn over compost piles regularly.

For more information on West Nile Virus and the health department’s surveillance activities, call the health department’s environmental help line at 905-723-3818 or 1-888-777-9613 or visit