SASKATOON, Saskatchewan (Reuters) – Canadian officials don’t know how two Canadian hog farm workers contracted a new flu virus, as the pigs tested so far on the farm where they work have demonstrated a common flu strain, not the new virus.

The new virus, which Canadian officials announced on Tuesday and have reported to the World Health Organization, contains genes from a seasonal human H1N1 flu strain and a flu virus common in the swine population called triple reassortant H3N2.

The virus is not connected to the new H1N1 strain that has killed 429 people worldwide.

“(The new virus) causes some concern because if it came from pigs, which we don’t know, it fuels the fire for people who view the pig as a mixing vessel (for flu viruses),” said Dr. Keith Campbell, national manager of animal biosecurity for the Canadian Food Inspection Agency.

He was speaking at a conference in the western province of Saskatchewan hosted by the newly formed Canadian Swine Health Board.

Campbell declined to speculate on other potential sources of the new flu virus.

“For my purposes, (the source) is not that important, but if I’m a pig producer, I don’t want people to think it came from pigs.”

Saskatchewan animal health officials have tested only a fraction of the 15,000 to 20,000 pigs on a corporate farm in Saskatchewan where the workers are employed.

The farm’s veterinarian tested pigs showing mild cough and respiratory symptoms, some of which tested positive for flu virus H3N2, not the new flu virus, said Dr. Greg Douglas, Saskatchewan’s chief veterinary officer, in an interview with Reuters.

He said he won’t know if that H3N2 strain is the same as the H3N2 strain in new virus until further lab tests are complete.

Douglas said that despite the test results, he assumes pigs transmitted the new virus as officials don’t believe it was transferred among humans.

“But I would be very careful in deducing that this virus in these humans came from somewhere specific,” Douglas said.

More pigs will now be tested on the farm. Farm owner Big Sky Farms, one of Canada‘s biggest pig producers, has voluntarily agreed not to move the pigs, but the farm is not under quarantine.

Saskatchewan health officials have tested about 500 samples submitted from people with flu-like symptoms in the past few weeks and found only the two hog workers and a third possible case showing the new virus, said Dr. Saqib Shahab, the province’s deputy medical health officer.

When Saskatchewan’s lab analyzed the workers’ samples, it found signs of both the seasonal human H1N1 flu and the swine H3N2 flu. Through genetic sequencing, Canada’s national lab determined the sample was a new virus, not a sample with two separate viruses present, Shahab said.

Health officials are now asking all hog farm workers in south-central and southeast Saskatchewan with flu-like symptoms to be tested, he said. The hog farm is in eastern Saskatchewan.

Canada does not require regular mandatory on-farm testing of swine, leaving it up to farmers.

“We have no intention to change that,” the CFIA’s Campbell said.

Flu symptoms in livestock are unique enough that farmers often diagnose them themselves, said Dr. George Charbonneau, president of the Canadian Association of Swine Veterinarians.

“As far as we’re concerned, (it’s) situation normal,” he said of the new flu virus. “To have these new strains evolving and showing up in the human population or the pig population — it’s just always been happening.”

(Editing by Peter Galloway)