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Topic: New study on AI genesis in China 對「禽流感源自中國」的新研究 (Read 1615 times) |
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Carrie Ma
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New study on AI genesis in China 對「禽流感源自中國」的新研究
« on: Feb 7th, 2006, 6:25pm » |
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Another message from in Asia Pacific Migratory Waterbirds e-mail group.
----Original Message-----
From: Taej Mundkur
Sent: Tuesday, February 07, 2006 3:51 PM
Subject: [APMW] Second Web Article: New study examines bird flu's genesis in China
Apologies for cross-postings.
Further to the email just sent with the News Scientist report on a new study examines bird flu's genesis in China, attached is a second article with additional insights based on interviews of the main authors.
With best wishes, Taej
Dr. Taej Mundkur
Wetlands International - South Asia
http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20060206/avian_flu_s tudy_060206/20060206?hub=Health
New study examines bird flu's genesis in China
Updated Mon. Feb. 6 2006 6:58 PM ET
Canadian Press
TORONTO — Genetic analysis of H5N1 avian flu viruses collected from wild and domestic birds in China suggests the virus has spread in uncontrolled fashion in southern China for the past decade, igniting outbreaks in Vietnam on at least three occasions and triggering spread of the worrisome virus across Russia to eastern Europe, a study released Monday suggests.
The study also provides what could be a smoking gun in the heated dispute about whether migratory birds are actually playing a role in moving the virus across the globe. A number of wildlife experts have insisted migratory birds are not to blame, but this study contends genetic analysis shows there can be no other explanation.
"I've spent most of my life working with wild birds and I'm sympathetic. But you can't hide the facts that wild birds are most probably involved in the spread of this thing now,'' said leading avian influenza expert Dr. Robert Webster, one of the authors of the paper.
Webster and his co-authors -- researchers from institutions in China, Hong Kong, Vietnam and Indonesia -- argue the only way to minimize the damage done by the virus and reduce the risk it poses to human health is by addressing the problem at the virus's birthplace, in the poultry flocks of southern China.
"We have shown that H5N1 virus has persisted in its birthplace, southern China, for almost 10 years and has been repeatedly introduced into neighbouring (e.g. Vietnam) and distant (e.g. Indonesia) regions, establishing 'colonies' of H5N1 viruses throughout Asia that directly exacerbate the pandemic threat,'' they said in the article, published in the Proceedings of the National Academy of Sciences.
"Therefore control of this regional epizootic and its attendant pandemic threat requires that the source of virus in southern China be contained.''
Doing that won't be easy, especially in light of another finding Webster and his colleagues reported.
They discovered instances where seemingly healthy chickens in Chinese poultry markets were shedding the virus. To date, chickens have been like the proverbial canaries in the coal mine with H5N1, which has killed millions of chickens across Asia.
It's not clear why the chickens didn't succumb to the virus. The authors suggest they may have been vaccinated or protected by previous exposure to a similar but not lethal virus. But one thing is clear: if chickens are able to survive infection but continue to shed the virus, tracing its spread will become much more difficult.
"It's not a case of `there are dead birds and they are hiding it'. (That) there are no dead birds is the problem,'' Webster said in an interview from Hong Kong.
"The pernicious thing is that there are these perfectly healthy birds that you walk into the markets day after day after day and the virus is always there.''
The researchers collected viruses over several years from wild birds in the Mai Po marshes of Hong Kong and at Poyang Lake in eastern China, and from swabs taken from apparently healthy poultry in markets across southern China.
They generated genetic sequences of the H5N1 viruses, comparing them to each other and to other previously sequenced viruses on what are called phylogenetic trees. These charts, the equivalent of a family tree, can identify where a virus came from by finding viruses to which it is most closely genetically related.
The charts the group generated suggest viruses from domestic poultry in southern China infected wild ducks in early 2005. Ducks took those viruses to Poyang Lake in eastern China and from there to Qinghai Lake in western China, more than 1,700 kilometres away. The viruses were responsible for a large die-off of wild birds at Qinghai Lake -- a wild bird reserve -- that occurred last May.
"That was the tipping point. The virus really got into the migratory birds at that point,'' Webster, who is based at St. Jude Children's Research Hospital in Memphis, Tenn., said of the Qinghai Lake incident.
Recent analysis of viruses from the first two human cases of H5N1 infection in Turkey showed they were closely related to viruses isolated at Qinghai Lake.
"Genetic relatedness of gene segments from H5N1 viruses isolated at Poyang and Qinghai Lakes strongly argues that migratory birds can transfer the virus over long distances,'' the authors said.
"This possibility may provide insight into reported H5N1 outbreaks in Mongolia, Siberian Russia and Europe that have been linked to migratory birds.''
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Carrie Ma
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Re: New study examines bird flu's genesis in China
« Reply #1 on: Feb 7th, 2006, 6:26pm » |
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(continue)
Earl Brown, a virologist who specializes in the evolution of influenza virus virulence, said the work done by this group helps scientists figure out what is going on with the H5N1 viruses.
"It puts details on the evolutionary story,'' said Brown, who is based at the University of Ottawa.
"This links the dots from southern China to this Poyang Lake to Qinghai. And then it sort of gets out from there even broader. But it's very important to know where the virus is coming from, what it's doing in the different places, like what birds (it infects) and what disease (it causes) and that sort of thing.''
The study also noted there are a number of distinct clades or families of viruses in birds. Previous genetic analysis of viruses isolated from human cases showed two distinct clades.
That finding has implications for production of vaccines against H5N1, as a vaccine produced using a virus from one clade might offer at best partial protection against a virus from another.
The authors suggest multiple seed strains or vaccine starters should be made and kept at the ready. The World Health Organization actually commissioned that work last October.
A WHO avian flu expert suggested this work is a reminder of how important it is to keep on top of how the virus is evolving.
"It's very important to do this kind surveillance so that we know what's going on. And we're hopeful, since there are some clear differences, that these viruses will be made available to other investigators to do further analysis,'' said Michael Perdue, who is with WHO's global
influenza program.
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