TORONTO - Canada is putting together a stockpile of 10 million doses of avian flu vaccine. But this one isn't for people.
The Canadian Food Inspection Agency has purchased five million doses apiece of poultry vaccines against H5 and H7 avian influenza viruses as a hedge against a possible outbreak of H5N1 or another highly pathogenic strain in domestic flocks.
It is also in the process of hammering out details of this year's program to look for avian influenza in wild birds. The program is designed in part as an early warning system to detect if the H5N1 viruses plaguing parts of Asia and Africa make their way to this continent in wild birds.
Dr. Jim Clark, the national manager of the agency's avian influenza working group, explained that while Canada's preference would be to control an avian flu outbreak in poultry by culling infected birds, vaccine could serve as an insurance policy of sorts.
"If there was an inability to control the disease using traditional stamping out methods, vaccine would be something that might be used to be more effective and dampen down the opportunity for the disease to spread so that we had an opportunity to get ahead of it," Clark said.
"And we want to be able to make sure that if we want to, we have the capacity to do that."
The vaccine is being purchased for US$468,300 from Fort Dodge Laboratories Inc. in Fort Dodge, Iowa and will be added to the 400,000 doses of an H5 vaccine the agency bought last year. Clark said the poultry vaccine would be expected to have a shelf-life of about two or three years or perhaps a bit longer.
Most avian flu subtypes are of low pathogenicity. When these so-called low path viruses make their way into domestic poultry flocks, there may be a decline in egg production but infection does not trigger mass die-offs of birds. Vaccine would not be needed to contain outbreaks of these strains.
But the H5 and H7 families of viruses have the capacity to become highly pathogenic as they circulate through poultry flocks, spreading swiftly and leaving mountains of dead birds in their wake. The economically devastating outbreak in British Columbia's Fraser Valley in the spring of 2004 was a low path H7N3 that ratcheted up to high pathogenicity.
Clark said the H5N3 vaccine the agency has purchased has been shown to be effective against the virulent Asian H5N1.
The H7N3 vaccine has also been shown to protect against a variety of subtypes of neuraminidase - the N in a flu virus's name.
"So what works with an H7N3 will work with an H7N1 versus an H7N6 or whatever," he said.
Clark said this year's wild bird surveillance program is still on the drawing board, but the goal is to increase the number of birds sampled to 16,000 this year from 12,000 last.
Earlier this month, U.S. officials announced they plan to take samples from about 27,000 birds, which is about the same number as last year.
Focusing on taking the right samples could make the difference between finding viruses and not, said Dr. David Halvorson, an avian influenza expert at the University of Minnesota.
Avian flu viruses typically live in the guts of birds - meaning the best place to swab would be the back end. But Halvorson pointed out that ducks have been shown to excrete Asian H5N1 viruses through their respiratory tracts, like people shed flu viruses.
"So you might get the right bird and sample the wrong end," he noted wryly.
Both the Canadian and U.S. programs plan to put increased emphasis on the detection, collection and sampling of dead birds.
"We're very much interested in submissions of dead birds this year as a clear indicator of whether there might be an H5N1 Asian strain causing that kind of die off," Clark said.
"Clearly in Europe and other places in the world, dead birds have offered the best insight into presence of the H5N1 virus."
Despite increased surveillance over the past couple of years, no evidence of the Asian H5N1 strain has been found in North America.
Veterinarians who've studied avian influenza over the years had expressed doubt this group of viruses would make its way to the continent in the guts of wild birds, noting genetic analysis shows there are distinct families of viruses, with little if any mingling of those from Eurasia and those found in the Americas.
