Wild birds in Canada's central province of Manitoba have tested positive for a low-pathogenic subtype of the H5N1 avian flu virus, a health official said on Saturday.

The strains are from the family of North American H5N1 viruses,not the forms circulating in Southeast Asia, said Dr. Brian Evans,chief veterinary officer at the Canadian Food Inspection Agency (CFIA).

"I want to emphasize that the H5N1 subtype detected in Manitobais completely distinct from the strain currently present in Asia,"said Evans

"From a genetic perspective, there are significant strain differences in their structure," he said.

In addition, officials isolated an H5N3 subtype in two birds from Quebec, as part of a cross-country surveillance program to find what avian flu viruses are being carried by wild ducks in this country.

"Finding only low pathogenic avian influenza means that these viruses would cause only mild disease, if any at all, if introduced into domestic birds," Evans said.

Meanwhile, a commercial farm in British Columbia's Fraser Valley remains under quarantine after a duck was found infected with a strain of H5 bird flu on Friday.

North American H5N1 viruses have so far proven to be much milder viruses than their distant Asian counterparts, avian influenza experts say.

"We've got 32 years of surveillance work that says these North American strains in wild birds in the past have never been a threat," Dr. Richard Slemons, an avian influenza expert at Ohio State University, told The Canadian Press.

"Does that mean they won't be a threat in the future? No it does not. But history says they aren't a risk," he said.

The Asian H5N1 viruses, which are highly pathogenic, have infected 130 people in five countries since 2003 and 67 of those people have died.