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Summer's blight, West Nile, here to stay In six short years, the virus has established itself as a Canadian fact of life. The vagaries of weather make scientists reluctant to predict how bad this season will be

In six short years, the virus has established itself as a Canadian fact of life. The vagaries of weather make scientists reluctant to predict how bad this season will be

Canadian Press

Dr. Ross Findlater is hoping West Nile virus has tired of battle-scarred Saskatchewan. But Dr. Bonnie Henry fears the fickle virus is turning its attention to her province, lush and lovely British Columbia.

With the weather warming, public-health officials across the country are again making cautious predictions about the famously mercurial virus that has established itself as a fact of summer in North America in the span of six short years.

But few in the field are willing to lay heavy wagers, having learned over those half-dozen seasons that West Nile is a viral will-o'-the-wisp that defies prognostication.

"We're certainly not making any hard predictions on what's going to happen. It's so dependent on the weather and things that we don't know," admits Dr. Findlater, Saskatchewan's chief medical officer of health.

Take last summer, for example.

Everyone was certain West Nile was going to complete its westward assault by moving into B.C. Recollecting Saskatchewan's brutal battle in 2003 -- 947 cases, Canada's worst West Nile outbreak ever -- B.C. braced itself for an onslaught. None came -- not in B.C or anywhere else. Canada recorded a mere 26 cases of West Nile virus last summer, down from 1,388 the year before.

Experts attribute the low case count to the lousy summer most parts of the country suffered through, though paradoxically British Columbians didn't have the cold, damp weather that left their fellow Canadians grumbling.

But the virus did make significant inroads in California and as far up the Pacific Coast as Oregon. So again this year, authorities are predicting West Nile will make its debut on the Canadian West Coast.

That's because migratory birds -- the long-distance truckers of the West Nile virus world -- run that route, called the Pacific flyway. "The birds that might be carrying West Nile virus from California and Oregon migrate north to British Columbia around this time of the year. And if they're carrying the virus, then it's absolutely certain that it will take hold in B.C.," says Dr. Henry, an epidemiologist who is overseeing the West Nile program run by the B.C. Centres for Disease Control.

Birds import the virus to a region, but it is mosquitoes that do the damage. They feed on the infected birds and pass the virus on to other uninfected birds, or hosts like horses. As new mosquitoes feed on them, the amount of virus in an area amplifies, eventually finding its way to mosquitoes that bite humans.

Human cases generally start to materialize by mid to late July. The vast majority of infected people don't even feel sick. But a small proportion develop severe neurological disease, and some die.

The amplification process requires the right kinds of mosquitoes and a summer with enough sustained heat to work up a viral head of steam.

So far, that process hasn't become seriously entrenched in Atlantic Canada. And the North has evaded West Nile's grasp -- though whether that will remain the case isn't clear.

"With climate change, I would imagine that becomes a somewhat greater risk," says Paul Sockett, director of the Foodborne, Waterborne and Zoonotic Infections Division of the Public Health Agency of Canada.

"How far north it would go is another question entirely. I certainly wouldn't want to make any predictions from that perspective."

In fact, Dr. Sockett believes the whole business of predicting West Nile's patterns is "fraught science." He thinks everyone should just assume West Nile is here and here to stay.

"Because we had a poor year last year in terms of numbers, that does not predict that we're going to have a poor year this year," he cautions.

"Which is why I think it's important to make sure that the public are aware that this is an ongoing risk from their perspective."

The way to respond to that risk boils down to a single recommendation that is easier said than done in this bug-infested land: Avoid being bitten by mosquitoes.

That means applying and reapplying appropriate mosquito repellents, wearing long sleeves and long pants from dusk till dawn, and ensuring that there are no pools of standing water around your home where mosquitoes can lay eggs.

Dr. Henry believes British Columbians, who've seen the virus's cross-country march, are ready for West Nile. "People here are primed. They understand the messages that have been going out for the last few years. They know what has happened in other parts of the country and North America."

The virus at a glance

Name: Derived from the area in Uganda where the virus was first identified in 1937.

North American debut: New York, 1999.

Canadian debut: Southern Ontario, 2001, in birds and mosquitoes. First human cases diagnosed in the summer of 2002.

Range to date: Quebec, Ontario, Manitoba, Saskatchewan, Alberta. Cases in Nova Scotia, New Brunswick, British Columbia and the Yukon believed to be linked to travel.

Approved mosquito repellents: Effective active ingredients are DEET, lavender, citronella, soybean oil or lemon eucalyptus. Apply according to label instructions.

Read more: http://www.phac-spc.gc.



Canadian Press

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