VANCOUVER - Three of four of the most recent avian flu outbreaks in Canada have broken out in British Columbia's Fraser Valley but despite years of trying to figure it out, they still can't explain why the valley attracts the virus.
In the latest outbreak, 60,000 turkeys were culled on an Abbotsford, B.C., farm last week.
Tests so far indicate the virus has not spread to any other poultry producers within a three-kilometre quarantine zone.
That wasn't the case in the valley's first outbreak in 2004 when an H7-type flu transformed into a highly contagious strain.
Farm after farm was quarantined until finally about 15 million birds -- almost the entire valley poultry population -- was destroyed.
The second Fraser Valley outbreak in November 2005 saw two duck farms infected with the H5N2 strain of the virus.
In 2007, a highly pathogenic H7N3 strain was found in Saskatchewan on a farm that produced hatching eggs to produce broiler chickens.
Experts have difficulty explaining why the Fraser Valley has been hit so often but there are theories.
"We're on the Pacific flyway so there are lots of birds passing through every year," says Ron Lewis, the chief veterinary officer for British Columbia.
"And we know wild waterfowl carry a variety of different strains of avian influenza."
People can easily walk over the areas where wild waterfowl have been.
"And we know avian influenza has some capability of aerosol transmission," he says.
Lewis and Sandra Stephens, veterinary program specialist with the Canadian Food Inspection Agency, suspect the main culprits are the wild birds moving throughout North America and the world on migratory flyways.
Avian influenza virus is prolific and when wild waterfowl have it "they shed tremendous numbers of viral particles."
"All these birds when they get to their summer or wintering grounds they co-mingle," says Stephens.
And North American flyways are not completely isolated from others.
"Although you tend to think of the North American flyways as being separate from Europe and Asia, in fact there is some crossover in the northern breeding grounds," she says.
The huge concentration of commercial poultry producers in the Fraser Valley is also a factor in the spread.
Any poultry producer faces being exposed to migratory birds.
"But where we have more concerns are areas like the Fraser Valley or the Niagara Peninsula where there are large concentrations of poultry farms close together," says Stephens.
Calvin Breukelman of the B.C. Poultry Association estimates there are about 600 poultry producers in the Fraser Valley in an industry worth close to $1 billion.
Such concentration occurred for obvious economic reasons: close access to a large market.
"In an ideal world we of course wouldn't have this concentration but it's not ideal and we have to do whatever we can to reduce the impact of that concentration," says Lewis.
Perhaps the biggest worry facing producers and the general population is the likelihood of the highly pathogenic H5N1 virus that killed hundreds of people in Asia, Africa and Europe occurring here.
Lewis suggests it's highly unlikely.
In countries where H5N1 occurred there are very close living conditions between poultry and people, he says.
"We don't have that kind of proximity to wild and commercial ducks co-habiting in many cases that is present in those countries," he says.
Moreover, Lewis says, the intense biosecurity measures introduced in Canada after the 2004 Fraser Valley outbreak are not practised in many of those countries.
"We now have a mandatory biosecurity program in place for all of the commercially-regulated poultry industry," he says.
"The industry has achieved a very high level of compliance with those biosecurity protocols," says Lewis, estimating the compliance rate at about 98 per cent of the industry.
Initial testing for avian viruses also can now be done in Abbotsford.
"So we have eliminated the delays in having to ship samples for testing at the federal lab," says Lewis.
Poultry producers in the Fraser Valley are still awaiting tests on the latest outbreak determining how contagious the virus may be.
"It sometimes can take a number of weeks to get the result," says Stephens.
The presence of H5 virus has been established but its specificity, or neuraminidase subtype which is the N in the virus name, isn't known yet.
That H5 virus was detected in some turkeys on a property owned by two brothers last month.
The avian flu has many different sub types with 16 different H's, or hemagglutinin, and nine different N's, meaning there are 144 possible combinations of the flu virus.
The virus must be grown in a lab culture and the latest sample has taken longer than expected.
"Some viruses grow (in a lab culture) more readily than others and there's no way of knowing which virus will grow quicker than another," says Stephens.
