Conditions creating ‘perfect storm’ for West Nile outbreak in Ontario, says expert

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A West Nile “epidemic” that could see more than 330 human cases in Ontario is imminent, according to a report released by researchers at Brock University Tuesday.

A team led by Fiona Hunter, a medical and veterinary entomologist, analyzed 12 years of data, examining human case prevalence, mosquito surveillance and climate statistics from across the province with the goal of predicting outbreaks.

The professor said the results are worrying, especially for Toronto, the Golden Horseshoe and Windsor-Essex, which are typically hardest hit by the virus.

“The peak will either be this week or next week,” Hunter explained. “We are looking at over 250 positive pools to date that will translate into about 339 human cases by year’s end if this is the peak week.”

Fiona Hunter

Fiona Hunter is a medical and veterinary entomologist at Brock University. She led a team that analyzed 12 years of West Nile data to predict when the next outbreak would happen. (Fiona Hunter)

Ontario saw outbreaks of the virus in 2002 with 395 human cases and in 2012 when 220 confirmed and probable cases were tallied. This year, there have been 14 reported — confirmed or probable — cases of West Nile virus in humans.

“These confirmed human cases are generally people who are pretty sick,” added Hunter. “That means there are a lot of other people out there who have been infected.”

A perfect storm of conditions

Hunter has been tracking the two main mosquito species that drive the rate of infection and said the number of mosquito pools that have tested positive for the virus have continued to rise each week and appear to be reaching their highest point.

Warm temperatures and strong mosquito populations are both factors in the higher-than-normal number of cases, according to the professor, who said the virus has been steadily “amplifying” in the background.

“Sometimes everything combines to make the perfect storm and this year is one of those years,” Hunter said.

Positive mosquito pools graph Ontario

This graph from Public Health Ontario shows the number of positive mosquito pools as well as human cases of West Nile Virus in the province since 2002. (Public Health Ontario)

As the summer comes to a close, mosquitoes will switch from biting birds to searching for any source of food, Hunter added, meaning more people could be exposed.

“Essentially they become less choosey so they’ll take whatever meal they can get and it if happens to be a human then they’re at risk of transmitting the virus,” she explained.

Now is the time to protect yourself

Although the swarms of mosquitoes that plagued people during the spring have died off, Hunter said the late summer is the most important time for people to protect themselves.

“I’ve seen repellent on sale at the grocery store right now because people figure that’s the end of the season,” she said. “But no, you should run out and grab it and use it.”

Ways to protect yourself from West Nile:

  • Use insect repellent that contain DEET
  • Ensure doors and window screens are free of holes and gaps
  • Limit time spent outdoors at dawn and dusk
  • Wear long-sleeved shirts and pants in light colours when outdoors

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Conditions creating ‘perfect storm’ for West Nile outbreak in Ontario, says expert

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