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West Nile virus remains a threat, scientists warn

Canadian Press

Last summer, the purveyors of black humour joked that a Canadian was someone who had sworn off beef, adopted hospital masks as the fashion accessory of choice and given up cologne for a liberal dousing of eau de DEET.

Fading fears about mad-cow disease mean steaks and burgers are back on the barbecue, SARS is a dim memory, and there doesn't seem much to fret over when it comes to the West Nile virus.

Or does there?

Canada has had no human cases of the mosquito-borne disease so far this year, and dead birds testing positive for the virus have been found in just four provinces. But experts say Canadians aren't out of the woods.

Disease specialists caution against taking an easygoing stance toward the disease, which they believe is here to stay.

A Health Canada report found in mid-spring that just four in 10 Canadians were taking steps to protect themselves from the disease.

"I think it is wrong to be complacent," said Karim Kurji, associate chief medical officer of health for Ontario.

"I think the difficulty here is that folks may not necessarily appreciate how bad West Nile virus can be. While in the majority of incidents it may be relatively symptomless, we know that in one in 150 individuals it can be very severe and lead to many debilitating effects."

It can kill, too. Last year, West Nile was diagnosed in 1,200 Canadians, and 10 of them died, most in Saskatchewan. The year before, 340 contracted the virus in Canada and 20 died, 18 in Ontario and two in Quebec.

In 2003, seven provinces -- Nova Scotia, New Brunswick, Quebec, Ontario, Manitoba, Saskatchewan and Alberta -- reported West Nile activity.

So far this year, the virus has been detected in fewer than 100 dead birds in Quebec, Ontario, Manitoba and Saskatchewan. Most have been found in Ontario.

Prince Edward Island and Newfoundland have never recorded the virus, and experts believe it is unlikely to strike the Rock because the kind of mosquito that typically carries the virus doesn't breed there. But they say West Nile should eventually make its way to PEI, which does have those mosquitoes.

Alberta had its first cases, both in humans and birds, last year, and because the virus was detected up to its western border, epidemiologists believe British Columbia will be next on the list.

Individuals are urged to use repellents containing DEET, wear light-coloured clothing that covers exposed skin, and eliminate stagnant water in areas such as in birdbaths, pool covers and leaf-filled eavestroughs where mosquitoes can lay eggs.

Unseasonably cool temperatures across much of the country may be one reason West Nile has simmered at low levels, said Harvey Artsob, director of zoonotic diseases at the National Microbiology Laboratory in Winnipeg.

"Weather can be an important factor," Dr. Artsob said. "One has to look at how quickly the virus is replicating and how many more mosquitoes are being infected. Weather in the Prairies has slowed things down a bit because it's been pretty cool. But that could change if the weather suddenly gets very hot, of course."

That is exactly what has happened in Saskatchewan, which recorded only two positive birds by mid-July, said entomologist Philip Curry, the province's West Nile co-ordinator.

"Now that we've got hot weather -- we're finally into our warm season here -- what we're watching to see is if there's this ramp-up in bird numbers that are positive."

While some may believe West Nile is waning in the East and gaining in the West, disease specialists say it is a mistake to believe the virus has a predictable pattern.

"I think what's surprising about West Nile is that it's a disease that will fool you," Mr. Curry said.

Ontario, for instance, was the West Nile hot spot in 2002. Last year, the case load dropped to 89, with two deaths.

Yet by July 15 this year, it had the highest number of confirmed virus-positive dead birds, at 60, followed by Quebec with 14, Manitoba with three and Saskatchewan with two.

Ontario has detected no positive mosquitoes in traps and no infected humans, but Dr. Kurji said the rise in virus-laden birds means human cases should follow in about five to six weeks, especially if there is a prolonged burst of hot weather.

"To be very frank, it's only a matter of time," he said.

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