OTTAWA - The swine flu spreading through Canada and Mexico is the same strain even though it has killed 42 Mexicans and been relatively mild here, Canadian scientists have found.
Researchers at the National Microbiology Laboratory in Winnipeg are the first to genetically sequence the H1N1 virus, officials said Wednesday.
And they have ruled out a mutation to explain why the Mexican cases have been much more severe than elsewhere.
One possibility being considered is that the Mexican victims may have had underlying medical conditions that made them more susceptible to the bug.
Canada's cases have all been mild, with the exception of a young Alberta girl who came down with a severe case of the flu.
Frank Plummer of the National Microbiology Laboratory said scientists worked day and night to sequence the virus in less than a week.
"We're continuing our analysis, but essentially what it appears to suggest is that there's nothing at the genetic level that differentiates this virus that we've got from Mexico and those from Nova Scotia and Ontario that explains apparent differences in disease severity ...
"That's one of the big questions that everybody's been asking, so part of the answer is that it's likely not the virus itself that is explaining the differential and severity of disease between Mexico and the rest of North America."
Plummer said he hopes the breakthrough will help to identify origin of virus and reveal how it spreads and mutates.
Officials have said Canada's only severe case -- involving a girl in an Edmonton hospital -- had more to do with underlying conditions than it did with the virus itself.
The girl, who has not been identified, is getting better and is breathing on her own.
It remained unclear how the girl, whose age was not released, became infected.
Canada added 25 cases to its confirmed case list Tuesday, bringing the national total to 165.
Two schools in British Columbia have been closed due to flu cases.
In Nova Scotia, a school that was one of the first in Canada to report cases stayed open despite the quarantine of a number of students and staff.
The Public Health Agency's website says, on average, the common flu sends about 20,000 Canadians to hospital each year. Between 4,000 and 8,000 can die of influenza and its complications annually, depending on the severity of the season.
