WHO confirms avian flu infections in Canada
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《英国医生杂志》
Calgary
Canada has ordered the slaughter of about 19 million birds, including chickens, turkeys, ducks, geese, and pigeons, at 20 poultry farms in an effort to eradicate an outbreak of bird influenza. The World Health Organization has confirmed that there have been two human cases of avian influenza A (H7) in British Columbia, Canada. Both cases were mild.
On the basis of epidemiological information provided by Health Canada, WHO has raised the global pandemic preparedness level for the Canadian outbreak from 0.1 to 0.2—the same level as the global preparedness level for the avian flu outbreak in Asia. In Asia, the highly pathogenic avian flu virus strain A (H5N1), has been responsible for 34 reported illnesses in humans and 23 deaths.
According to the Canadian Food Inspection Agency, the strain of influenza identified in the poultry flocks is likely to be an H7N3 virus.
Public health officials in Canada are concerned because the H7 virus is a new subtype of influenza that can cause illness in humans. This increases the risk that the virus can undergo genetic modification that will allow it to acquire the ability to spread from person to person. Should this happen in conjunction with changes in its level of pathogenicity, the stage would be set for a flu pandemic.
Recent research has shown that viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses. During a 1999-2001 epidemic in Italy, for example, the H7N1 virus, initially of low pathogenicity, mutated within nine months into a highly pathogenic form.
So far, there has been no evidence of person to person transmission of the H7 virus, said Dr Danuta Skowronksi, an epidemiologist at British Columbia's Centre for Disease Control. The two Canadians with laboratory confirmed infection with the A (H7) virus both had direct contact with infected birds. Both fully recovered after being treated with oseltamivir.
Canada's National Microbiology Laboratory in Winnipeg, Manitoba, is working closely with WHO to try to develop a seed vaccine for the H7 avian flu virus. The laboratory has forwarded strains of the virus to the WHO Collaborating Centre.
"From the point of view of preparing for pandemic influenza and responding to an eventual influenza pandemic, it's important to globally have as much capacity as possible," said the laboratory's scientific director, Dr Frank Plummer. "Working simultaneously in a coordinated way on development of a vaccine is a very important goal."
The reason for working on a vaccine is partly because of a very low possibility that the H7 strain might become a serious health concern and partly as an exercise in strengthening emergency preparedness for the next pandemic, said Dr Plummer.
Last year, outbreaks of H5N1 avian flu were detected among poultry in China, Vietnam, Thailand, Cambodia, Indonesia, Laos, Japan, and South Korea (14 February, p 368).(Barbara Kermode-Scott)
Canada has ordered the slaughter of about 19 million birds, including chickens, turkeys, ducks, geese, and pigeons, at 20 poultry farms in an effort to eradicate an outbreak of bird influenza. The World Health Organization has confirmed that there have been two human cases of avian influenza A (H7) in British Columbia, Canada. Both cases were mild.
On the basis of epidemiological information provided by Health Canada, WHO has raised the global pandemic preparedness level for the Canadian outbreak from 0.1 to 0.2—the same level as the global preparedness level for the avian flu outbreak in Asia. In Asia, the highly pathogenic avian flu virus strain A (H5N1), has been responsible for 34 reported illnesses in humans and 23 deaths.
According to the Canadian Food Inspection Agency, the strain of influenza identified in the poultry flocks is likely to be an H7N3 virus.
Public health officials in Canada are concerned because the H7 virus is a new subtype of influenza that can cause illness in humans. This increases the risk that the virus can undergo genetic modification that will allow it to acquire the ability to spread from person to person. Should this happen in conjunction with changes in its level of pathogenicity, the stage would be set for a flu pandemic.
Recent research has shown that viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses. During a 1999-2001 epidemic in Italy, for example, the H7N1 virus, initially of low pathogenicity, mutated within nine months into a highly pathogenic form.
So far, there has been no evidence of person to person transmission of the H7 virus, said Dr Danuta Skowronksi, an epidemiologist at British Columbia's Centre for Disease Control. The two Canadians with laboratory confirmed infection with the A (H7) virus both had direct contact with infected birds. Both fully recovered after being treated with oseltamivir.
Canada's National Microbiology Laboratory in Winnipeg, Manitoba, is working closely with WHO to try to develop a seed vaccine for the H7 avian flu virus. The laboratory has forwarded strains of the virus to the WHO Collaborating Centre.
"From the point of view of preparing for pandemic influenza and responding to an eventual influenza pandemic, it's important to globally have as much capacity as possible," said the laboratory's scientific director, Dr Frank Plummer. "Working simultaneously in a coordinated way on development of a vaccine is a very important goal."
The reason for working on a vaccine is partly because of a very low possibility that the H7 strain might become a serious health concern and partly as an exercise in strengthening emergency preparedness for the next pandemic, said Dr Plummer.
Last year, outbreaks of H5N1 avian flu were detected among poultry in China, Vietnam, Thailand, Cambodia, Indonesia, Laos, Japan, and South Korea (14 February, p 368).(Barbara Kermode-Scott)