VANCOUVER - Two more farms in southwestern British Columbia were placed under quarantine Wednesday as officials attempted to contain an outbreak of avian influenza, though it wasn't yet clear whether any birds at the new sites were actually infected.

The announcement brought to four the number of farms in B.C.'s Fraser Valley under quarantine, and it came as several markets in Asia imposed restrictions on Canadian or B.C. poultry.

The outbreak began at a turkey farm in Abbotsford and a chicken farm in Chilliwack, which were quarantined earlier this week after birds at both sites tested positive for H5 avian influenza. A combined total of 18,000 birds at the farms have either died or will be euthanized.

The Canadian Food Inspection Agency said it placed the additional two farms under quarantine after learning they each received chickens from the infected Chilliwack operation last week. One of the new farms is in Chilliwack, while the other is in Abbotsford. One of those two farms has also seen unexpected bird deaths.

Dr. Harpreet Kochhar, Canada's chief veterinary officer, said the food inspection agency is awaiting test results to confirm whether any birds at the farms were infected.

"This is just a suspicion," Kochhar said during a conference call with reporters.

"There is also a risk, given that there is an integrated poultry industry in the Fraser valley, that there might be situations where other at-risk farms are identified."

The agency is also waiting for test results to determine the specific N-subtype of the virus involved. Of particular concern is whether the virus is the dangerous H5N1 strain or H5N8, which is currently affecting farms in the Netherlands.

Officials have cautioned that the virus does not pose a risk to consumers if poultry meat is properly handled and cooked, though in rare cases it can be transmitted to people who work in close contact with the animals.

Hong Kong, South Korea, Taiwan and Japan have all imposed varying restrictions on poultry from B.C. and Canada due to the avian influenza outbreak.

Agriculture and Agri-Food Canada spokeswoman Miriam Wood said in an email that Japan has banned all Canadian poultry products, as well as the import of chicks from B.C.

South Korea has banned chicks from Canada, and Taiwan has banned all B.C. poultry and poultry products, she said.

As of Wednesday afternoon, the U.S. had not put in place any restrictions on poultry from B.C. or Canada.

Kochhar said it's possible that other countries may follow suit, though he hoped for a balanced response.

Hong Kong's Centre for Food Safety said in a news release that it has banned all poultry meat and poultry products, including eggs, from the Fraser Valley region "for the protection of Hong Kong's public health."

There have been avian influenza cases at farms in several Canadian provinces, though the most serious outbreak occurred in 2004 in B.C., also in the Fraser Valley, where the H7N3 strain of the virus spread to 42 commercial poultry farms and 11 backyard coups.

The outbreak led to temporary trade restrictions on B.C. poultry and prompted federal officials to order the slaughter of 17 million chickens, turkeys and other domestic birds.

Ray Nickel of the B.C. Turkey Growers' Association said the 2004 outbreak prompted widespread change to prevent the spread of avian influenza, including a new lab in Abbotsford and improved measures to prevent contamination.

In light of those changes, Nickel said he was "somewhat surprised and shocked" to learn of the current outbreak.

"We've put so much effort into some of our biosecurity and containment measures that we trust those mechanisms," said Nickel.

"They are risk-management measures, so it doesn't mean we're bulletproof."

Nickel noted the number of birds affected so far represents a relatively small proportion of the province's poultry industry, meaning consumers likely won't see the effects of the outbreak in grocery stores.

B.C.'s Ministry of Agriculture says the province's poultry industry produced 160 million kilograms of chicken in 2012, and 21 million kilograms of turkey.

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News from © The Canadian Press, 2014