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H5 Found in Wild Birds in Canada; Experts Think It's Unlikely the Asian H5N1

Posted on: Monday, 31 October 2005, 21:00 CST

By HELEN BRANSWELL

(CP) - Nearly three dozen wild waterfowl in Quebec and Manitoba have tested positive for H5 avian flu viruses, but federal officials were quick to stress Monday that it is not necessarily the dangerous H5N1 strain ravaging poultry stocks and occasionally infecting people in Southeast Asia.

In fact, many avian influenza experts said they felt it was unlikely the viruses will turn out to be of the H5N1 subtype, let alone the Asian variant that experts fear may be poised to trigger a human flu pandemic.

"I will be extremely surprised if these viruses are H5N1, Asian H5N1 viruses," said Dr. David Suarez, research leader for exotic and emerging avian viruses at the U.S. Department of Agriculture's Southeast Poultry Research Laboratory in Athens, Ga.

Others said the finding of H5 viruses was of no surprise.

"You would expect to find H5 viruses in Canadian birds," said Dr. Earl Brown, a virologist from the University of Ottawa who specializes in the evolution of influenza viruses. Brown noted an H5N9 virus was isolated from a turkey in Ontario in 1966.

Canadian officials said additional testing of samples taken from the birds - 28 in Quebec and five in Manitoba - should indicate by the end of the week whether the viruses are of the H5N1 subtype or another H5 variety.

Some privately questioned why Canada went public with the findings before it could say definitively what subtype or subtypes it had found and whether they were linked in any way to the Asian H5N1 viruses.

Officials of the Canadian Food Inspection Agency said the decision was taken to go for maximum transparency. Waiting for the viruses to be fully typed would have meant keeping the findings secret for over a week, said Dr. Jim Clark, acting director of the agency's animal health and production program.

"We don't want to take that particular approach. Open and transparent, give you what we know, the best information available," he explained.

Even if the viruses turn out to be H5N1, that doesn't mean they are closely related to the Asian strain, experts insisted. Molecular analysis of the viruses will have to be done to determine if they are linked. A different H5N1 could be far less dangerous than the ones circulating in Southeast Asia.

Typically there is little mingling of avian flu viruses from the flyways of Eurasia and the Americas, experts said.

"Almost without exception, if you just looked at a virus, you can tell whether it's from a North American lineage or a Eurasian lineage just by the sequence," Suarez said.

The announcement of the discovery is likely to generate headlines throughout North America and beyond and may raise questions among Canada's trading partners.

"I don't know what . . . your trading partners are going to say," noted Dr. Richard Slemons, an avian influenza expert at the Ohio State University.

But health officials insisted the findings poses no human health concerns at this point.

"We have no information suggesting that this poses any new threat to human health," said Dr. Arlene King, director of the Public Health Agency of Canada's immunization and respiratory infections division.

There are no reports in the scientific literature of people becoming infected with an avian flu strain passed on from a wild bird. All known human infections with avian flu strains were reported passed from infected domestic poultry to people - and even they are rare events.

But King cautioned that hunters should use proper hand hygiene and kitchen safety measures when dressing and cooking dead ducks.

Experts like Suarez, Slemons and Clark said that H5N1 viruses are rarely found in North America. On this continent, H5 viruses are more commonly of the H5N2 and H5N3 varieties.

As a subtype, H5 viruses aren't terribly common in North America, making up around five or six per cent of viruses typed over the years. Far more common are viruses of the H3 or H6 families.

But until recently, few resources were devoted to trying to find which avian viruses birds travelling through North America were carrying. So in many respects, experts said, this is yet another case where the maxim of surveillance - "Seek and ye shall find" - holds true.

"There's never been any financing to do this type of work," said Slemons, who has been collecting and typing avian flu viruses from migratory birds for over 20 years.

"Now there's a lot of money and there's a lot of people doing it. We'll find more (H5s)."

Clark also stressed the findings aren't a surprise.

"Experts worldwide know that this virus in one form or another has circulated among wild birds around the world for hundreds or perhaps even thousands of years," he told a news conference in Ottawa.

The birds were sampled as part of a surveillance program aimed at taking a census of avian flu viruses in wild water birds in Canada. Six laboratories - in British Columbia, Alberta, Manitoba, Ontario, Quebec and Prince Edward Island - were each aiming to sample 800 waterfowl across the country from August to late September, said Dr. Ted Leighton of the Canadian Co-operative Wildlife Health Centre at the University of Saskatchewan.

Clark said some labs didn't hit their targets, so somewhere between 4,000 and 4,800 samples were taken. Only Quebec and Manitoba have finished typing their samples; the remaining work should be completed over the next couple of weeks, he said.

Flu viruses are classified according to two proteins on their surfaces, the hemagglutinin (H) and neuraminidase. There are 16 known hemagglutinins and nine known neuraminidases, which can come together in 144 possible combinations. But some of those combinations have never been found, leaving flu experts to hypothesize some combinations cannot be formed.

Most viruses are of what's called low pathogenicity, posing little or no threat to human health and even modest threat to domestic poultry. Typically outbreaks of low path avian flu viruses lead to a drop off of egg production in domestic poultry.

But two subtypes of viruses, the H5s and the H7s, are sometimes found in what is known as a highly pathogenic form. Those viruses decimate poultry stocks.

The H5N1 in Asia is a high path virus; so was the H7N3 virus that caused the massive outbreak in British Columbia's Fraser Valley in 2004.

Source: Canadian Press

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