Vancouver — A tiny genetic difference in the avian flu virus infecting the Fraser Valley has made it a big killer, B.C. scientists have discovered.
Scientists knew soon after the virus began killing off Fraser Valley chickens in March that it was a rare and highly virulent strain of the H7N3 virus.
But after working out the virus genome — its genetic road map — they now know why.
More importantly, though, they also concluded the H7N3 virus that's killing chickens in massive numbers has never come into contact with any human genetic material.
Scientists have long been concerned the bird flu virus will get together with the human flu virus and create a deadly, easily transmittable virus in humans.
“The one thing that we're really, really afraid of and we've been running scared of is the possibility of a reassortment virus,” said Martin Petric, a virologist at the B.C. Centre for Disease Control.
“What we're able to show, is that no, this is entirely a chicken virus, it's one of those things that can't get into people.”
The entire population of chickens and turkeys in the Fraser Valley — about 19 million birds — are being culled in an effort to wipe out the virus that has devastated the B.C. industry.
The virus is now believed to have infected 40 commercial farms and another 10 smaller so-called backyard flocks. Another 200 farms have tested negative.
The H7N3 virus is normally not a quick killer, but something happened with the Fraser Valley strain, making it virulent, or as the scientists put it, highly pathogenetic.
Further alarming officials was the fact that two farm workers contracted pink eye, a mild human symptom of the virus.
The H7N3 virus is different from the H5 strain that has killed several people in Asia, as well as hundreds of thousands of chickens.
The H and N represent different proteins. There are 15 varieties of the H and nine of the N. The proteins combine in different ways to make up specific viruses, some of them more deadly than others.
The virus has eight genes.
In the Fraser Valley version, scientists discovered a protein associated with one of the genes contained amino acids in an area which helps determine how virulent the virus is, said Dr. Caroline Astell, project leader at the B.C. Cancer Agency's Genome Sciences Centre.
The amino acids didn't exist in a non-virulent strain of the virus found in the same area just east of Vancouver.
“It's suggesting, but it's not proving, that this is associated with the increased pathogenicity,” said Dr. Astell.
Figuring out the genome of the virus doesn't give any clues about whether that form of the virus will more easily combine with a human flu virus, said Dr. Robert Brunham, director of medical and academic affairs at the B.C. Centre for Disease Control.
But should that ever happen, the genomic code will be invaluable.
“We can respond faster in two ways,” he said.
“We now have the information to make a specific diagnostic test to see if this virus is present in humans, and should we need a vaccine, we have the information to rapidly make that vaccine.”
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