TORONTO - With swine flu viruses now showing they can infect humans, pigs and turkeys, scientists will be looking closely for genetic evidence of whether the viruses change in potentially dangerous ways as they pass from one species to another.
Unfortunately, the first known case where the virus likely passed from people to pigs back to people won't provide any answers.
The head of Canada's National Microbiology Laboratory has revealed his lab couldn't isolate viruses from respiratory specimens collected from two federal employees who became infected while investigating an outbreak of the novel H1N1 virus on an Alberta pig farm.
Though the two Canadian Food Inspection Agency inspectors tested positive for the pandemic flu virus, lab technicians would have to have found live viruses in their specimens to be able to compare them to those of viruses isolated from pigs on the farm and from other humans.
"We weren't able to isolate virus from what we got. So we haven't really sequenced anything," Dr. Frank Plummer said in an interview Friday.
"It's too bad, but I think that's just the way it is."
It's not uncommon that specimens don't yield viruses for study. But in this case it is unfortunate. Scientists would have liked to have seen whether the cycling through different species created changes in the viruses - and what kind of changes.
"It absolutely would have been very interesting," said Plummer, who admitted without live viruses "there's nothing really more to be done."
The pandemic virus was first found in people in mid-April. Late this week officials in Chile announced they had found the virus in turkeys - a species known to be susceptible to influenza viruses.
Though it is largely comprised of swine influenza genes, there is no evidence the virus is spreading in pig populations or that pigs are fuelling the spread among humans. In fact, in the handful of cases where the virus was found in pig herds - in Canada, Argentina and Australia - the presumption has been that people have infected pigs, not the other way around.
The first such case occurred in mid-to-late April in Alberta, on a pig farm near Rocky Mountain House.
It's not known and may never be known who introduced the virus into the pig population, but CFIA believes the source was human. And the agency also believes two of its inspectors who investigated the outbreak and came down shortly thereafter with swine flu picked up the virus in the piggery. The men admitted they took off their protective equipment because they were hot.
As for the viruses isolated from the pigs, the National Centre for Foreign Animal Diseases - the animal counterpart to Plummer's lab - is continuing to study the genetic sequences of those viruses.
But the lab's director, Dr. Soren Alexandersen, said the isolates don't seem to contain any significant changes when compared to the genetic sequences of the viruses circulating in people.
"They are very similar and more than 99 per cent similar," Alexandersen said. "There's nothing that looks specific or interesting at this point."
The lab, which shares a campus with the National Microbiology Laboratory, is also sequencing virus samples taken from a pig herd in Quebec where the novel H1N1 virus was found.
That work isn't yet completed, but Alexandersen said the picture so far is much like the one seen with the Alberta pig isolates.
"Nothing interesting or particular. It's again very, very similar," he said.