February 20, 2004

 

 

Canada Reports 1st Bird Flu Case

 

Canada on Thursday has confirmed its first case of bird flu in British Columbia. However the strain is not identical to the deadly flu virus spreading across Asia, experts say.

 

The H7 strain found at the farm on B.C.'s Lower Mainland is "leaps and bounds different from H5N1, where there's high lethality, not only in chickens but also in humans," influenza expert Dr. Danuta Skowronski of the British Columbia Centre for Disease Control said Thursday.

 

"But what we want to do - always, whenever there's an avian outbreak - is contain it and minimize human exposure."

 

Avian influenza strains don't spread easily to humans or among them. In fact, to date only H5 and H7 subtypes have been shown to occasionally have the ability to jump directly into humans from birds.

 

That was first documented in an H5 outbreak in Hong Kong in 1997. Before that it was thought bird flu strains had to pass through pigs, where the viruses picked up genetic material that allowed them to infect humans.

 

A widespread outbreak of H7 virus in poultry stocks in the Netherlands last spring infected 89 people, mostly farm workers, in that country. Most suffered only an eye infection called conjunctivitis, but several people developed influenza and one man, a veterinarian, died.

 

Whether they jump directly to humans or via pigs, avian influenza viruses are highly mutable and are always considered a potential threat to human health.

 

"The general picture is clear: bird disease is related to human disease when you're talking about influenza," said Earl Brown, a University of Ottawa virologist who specializes in influenza.

 

"What goes around in chickens comes around in people. ... This natural evolution has to be blocked."

 

The fear is that an avian influenza subtype that hasn't before circulated among people could learn how to do that - and that could trigger an influenza pandemic. No one would have any immunity to the novel virus and it would be expected to sweep the globe in a tidal wave of illnesses, deaths and widespread social disruption.

 

A highly pathogenic form of avian influenza would be expected to kill most birds it infected, while a less pathogenic strain would sicken but not necessarily kill flocks.

 

Even a strain of low pathogenicity would need to be addressed with urgency, Brown said.

 

"One thing that you can bet on with certainty is that if you get a low pathogenic virus in your chicken farm and don't stop it, it will turn into a highly pathogenic one every time. It's just an evolutionary thing."