The avian flu virus involved in an outbreak in British Columbia is related to a deadly strain that has spread through Asia and is now affecting North American poultry for the first time, the Canadian Food Inspection Agency says.

Experts say the presence of an avian flu virus with Asian lineage does not increase the danger to humans — which remains very low — but it could pose a significant risk to the poultry industry.

Nearly 250,000 chickens and turkeys at commercial farms have already been affected by the outbreak of avian flu, which has infected 11 other sites in B.C.'s Fraser Valley since the beginning of December. (Associated Press)

Nearly 250,000 chickens and turkeys are either dead or set to be euthanized due to avian flu, which has infected 11 sites in B.C.'s Fraser Valley since the beginning of the month.

Officials have already identified the subtype as a highly pathogenic, or high-path, strain of H5N2. Viruses with high pathogenicity kill birds, while their low-path counterparts typically do not.

The agency said tests have determined the virus contains genes both from H5N2, which is common to North American wild birds, as well as genes from a high-path Eurasian strain of H5N8. It keeps the label of H5N2 because its N gene is from H5N2.

"This is the first time a Eurasian lineage highly pathogenic H5 virus has caused an outbreak of avian influenza in poultry in North America," it said in a statement.

"The appearance of this particular re-assortant virus is significant due to its ability to cause high mortality in domestic poultry."

Not yet detected in wild birds

The agency has yet to determine the source of the outbreak or how it is spreading. The statement noted it has not yet been detected in wild birds in Canada.

Earlier this week, the U.S. Department of Agriculture confirmed two wild birds in Washington state tested positive for avian flu — one with H5N2 and another with H5N8. It's not clear whether those cases are connected in any way to the B.C. outbreak.

A worker in a bio-security suit prepares to cull poultry on a Fraser Valley farm in early December. (CBC)

Earl Brown, a University of Ottawa microbiologist who is an expert in the influenza virus, said a virus with Asian roots could be significant if it sustains itself in wild birds.

Brown said that in North America, avian flu typically infects farmed poultry in its low-path form, which often does not have a significant impact on operations. The virus can evolve into a high-path variety, but that doesn't always happen and it's a long process.

He said that doesn't appear to be what happened in the current outbreak.

"If you get bird flu into a poultry barn right now, most of the time you can get away with it because the virus won't adapt and won't evolve to high virulence," Brown said in an interview Friday.

"But if you have high-path in your wild birds, then every time there is a slip through biosecurity it will be seen as a big event of mortality. It really hinges on whether this virus stays behind in the wild birds."

Ray Nickel, president of the B.C. Poultry Association, said it's a concerning development for the industry because it means the virus is already in its high-path form when it first enters a barn.

"Our vigilance is going to have to be extraordinarily careful because it could be in the environment," Nickel said.

"It isn't like we'll get control, we'll clean this up and we won't have to worry about it anymore. We will continue to have to be very careful about environmental contamination."

Asian strain also in Europe

High-path H5N8 has been responsible for recent outbreaks in Asia and Europe, including in the Netherlands, Germany, Italy and the United Kingdom.

There have not been any cases of H5N8 transmitting to humans.

A cull of nearly 250,000 poultry birds is, or has, taken place at 11 Fraser Valley farms where the virus has been detected. (CBC)

Hundreds of people, primarily in East Asia and the Middle East, have been infected with H5N1, with more than half of them dying, while there has been one reported case of a human H5N6 infection.

Brian Ward, a microbiology professor at McGill University in Montreal, said the link to Asian influenza does not increase the risk to people in B.C.

"The fact that it's highly pathogenic is a big deal for birds," Ward said. "Human infection is very rare, and more importantly, from a pandemic point of view, human-to-human transmission is extremely unlikely."

The current outbreak began about three weeks ago, when officials from B.C.'s Ministry of Agriculture detected avian influenza on a turkey farm and a chicken farm.

The virus has now infected 11 sites in Chilliwack, Abbotsford and Langley. The latest, a chicken farm in Langley, was confirmed on Wednesday.

The most serious avian flu outbreak in Canada was in the Fraser Valley in 2004, when a high-path strain of H7N3 spread to 42 commercial farms and 11 backyard coups in the Fraser Valley. In response, the federal government ordered the slaughter of 17 million chickens, turkeys and other domestic birds.