New West Nile cases a reminder problem mosquitoes still active, province says

Six more people have tested positive for West Nile virus, a disease spread by mosquitoes still active in the province, officials with Manitoba Health said Friday.

Tiny disease carriers can thrive in hot, dry weather and often go unnoticed

Health officials have identified six new cases of West Nile virus in Manitoba this summer. (James Gathany/CDC)

Six more people have tested positive for West Nile virus, a disease spread by a particular species of mosquitoes active in the province, officials with Manitoba Health said Friday.

The report brings the total number of people infected in 2018 to seven.

Three cases were discovered in patients in the Interlake-Eastern region, two in the Prairie Mountain region and one in the Winnipeg region. The first case of West Nile was discovered in a child in the Southern Health region in early August.

"Sadly we were expecting this," said Dr. Richard Rusk, a communicable disease medical officer of health for the province.

Surveillance traps show the number of infected Culex tarsalis mosquitoes remain high throughout southern Manitoba, Manitoba Health said in a release.

"We had seen our numbers of positive mosquitoes going up over the last while. It usually takes two or three weeks before we start seeing the cases," Rusk said.

Culex tarsalis mosquitoes, which carry the West Nile virus, are so small most people won't see or hear them, and might not even know when they have been bitten. (Jeff Topping/Getty Images)

Two of the people with West Nile this year required hospitalization. All have since returned home, Rusk says.

Most people who contract the virus show no symptoms. Health Canada estimates between 70 and 80 per cent who are bitten are asymptomatic. 

The symptoms may feel flu-like, Rusk says. In severe cases, West Nile can cause painful headaches, swelling on the brain and, in rare cases, paralysis, coma and even death.

Last year, three people contracted West Nile. In 2016, 16 people became infected with the disease, according to Manitoba Health records.

Keep bug spray on

While the number of nuisance mosquitoes Winnipeg is famous for is low this year, Rusk says the species that carries West Nile remains prevalent.

Culex tarsalis are much smaller than the typical mosquito and are resistant to dry, hot weather. The species is so small, people may not feel their bites — and it only takes one bite to spread West Nile.

The fact they go unnoticed gives them an advantage. People may not bother to spray themselves with DEET if they don't see or hear the hungry insects.

"If you don't think you've got any mosquitoes in your backyard you don't try and prevent the bites," Rusk said. "Even now, if you're out on the patio this weekend, you need to be putting bug spray on."

Along with misting down, Rusk says people can prevent the spread of West Nile by wearing long, loose, light-coloured clothing and by repairing holes in screens. Culex tarsalis are known to be particularly active between dusk and dawn.

Rusk says Manitoba has no current plans to fog for mosquitoes this season.

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