Study warns of West Nile virus epidemic in Ontario this year

Aug 23 2017, 10:24 pm

There may be a spike in West Nile Virus (WNV) cases in Ontario this year, according to a recent study by Brock University researchers.

The study, West Nile virus in Ontario, Canada: A twelve-year analysis of human case prevalence, mosquito surveillance, and climate data, conducted by Bryan V. Giordano, Sukhdeep Kaur, Fiona F. Hunter, looked at records of the virus in mosquitoes between 2002 and 2013 along with climate data from seven municipalities to investigate the connection between temperature and the virus.

According to the researchers, there have been a number studies that have shed light on factors that affect WNV transmission, such as severity of the preceding winter, drought, rainfall, heatwaves, density of mosquito vectors, density of vertebrate hosts, landscape, and availability of mosquito breeding site abundance, but most have been in the US.

While WNV epidemics in Canada are difficult to study due to relatively low human case prevalence, large variations in the severity of outbreaks from year to year, and temperature dependency, the study states that temperature is proven to affect the incubation period, mosquito metabolism, and mosquito survival.

west nile

Public Health Ontario

And the researchers found that mosquitos carrying the virus are abundant in the late summer, historically when most WNV human cases occur in Ontario, and generally this time of year as the weather peaks in warmth.

The study identified the Greater Toronto Area (including Hamilton, York, Peel region, and Toronto) as hot spots of WNV activity. As of August 16, 2017, 31 mosquito pools have tested positive for WNV, according to the City of Toronto, who monitor mosquitos regularly.

Provincially, as of August 19, there have been 14 reported (confirmed or probable) human WNV cases and 264 WNV positive mosquito pools, from 26 different health units across the province.

And while this may sound like a lot of positive mosquitos, the City of Toronto has said that the risk of becoming infected is low.

“While the risk of becoming infected with West Nile Virus in Toronto is low, now is a good time to remind residents of the ways they can protect themselves from mosquito bites and help reduce the risk of infection,” said Dr. Eileen de Villa, Toronto’s Medical Officer of Health, in a release earlier this summer.

Toronto Public Health recommends the following tips to protect from mosquito bites:

• Wear light-coloured, long-sleeved shirts and pants when outdoors.
• Apply insect repellent containing DEET or icaridin and follow the manufacturer’s instructions.
• Take extra care during peak mosquito biting time (dusk and dawn) by using mosquito repellent and wearing protective clothing.
• Remove standing water from your property, where mosquitoes can breed.
• Ensure your home has tight-fitting screens on windows and doors.

In 2016, there were 19 confirmed human cases of West Nile Virus in Toronto. Toronto Public Health reports that so far in 2017 there have been no human cases of the virus reported in Toronto.

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