Carrie Ma
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Genes of deadly AI reveal Chi. origin 基因顯示禽流感源自中國
« on: Feb 7th, 2006, 6:15pm » |
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-----Original Message-----
From: Taej Mundkur
Sent: Tuesday, February 07, 2006 3:05 PM
To: Asia Pacific Migratory Waterbirds
Subject: [APMW] New Scientist Breaking News - Genes of deadly bird flu reveal Chinese origin
Dear all,
Attached is the New Scientist Breaking News on the web that provides new insights into the HPAI virus and its spread in the region by poultry movements and also migratory waterbirds.
A reading of the full paper Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0511120103) is also recommended.
This has implications for how we need to increase research into understanding precise waterbird migratory flyways and routes to develop appropriate response strategies.
With best wishes, Taej
Dr. Taej Mundkur
Wetlands International - South Asia
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New Scientist Breaking News - Genes of deadly bird flu reveal Chinese origin
http://www.newscientist.com/article.ns?id=dn8686
07 February 2006
Genes of deadly bird flu reveal Chinese origin
22:00 06 February 2006, NewScientist.com news service,
Debora MacKenzie
The H5N1 flu virus has been circulating continuously in poultry in south-eastern China for a decade, scientists have found. A massive genetic analysis shows the virus has mainly been spread by poultry, but also that wild birds carried it from southeast China to Turkey.
Yi Guan and colleagues at Shantou University, plus scientists in Xiamen and Hong Kong, say the only way to stop the virus is to control it in southeast China. The Chinese authorities have denied the country is the epicentre of the virus and opposed independent flu research.
The researchers analysed samples taken from 13,000 migratory birds and 50,000 market poultry in southeast China between January 2004 and June 2005, when the Chinese government banned independent sampling. In the markets, they found H5N1 in about 2% of apparently healthy ducks and geese, and some chickens, in all but two of the months in the sampling period.
The genetic make-up of the virus differed slightly between Guangdong, Hunan and Yunnan provinces, forming distinct geographic clusters. But they all descend from a 1996 Guangdong virus, and show the greatest genetic variation in Guangdong and neighbouring Guangxi and Hunan, showing they have been there longest.
Divergent strains
Robert Webster of St. Jude's Children's Research Hospital in Memphis, Tennessee, US, a co-author of the paper, says this shows the virus originated in those provinces, and has been circulating in the region ever since, long enough to evolve divergent strains.
These strains then "colonised" neighbouring areas. Viruses from Vietnam and Thailand match Guangdong viruses, while Indonesia has its own related cluster. Genes from Vietnamese viruses reveal repeated introductions from Guangxi, most recently in 2005. This contrasts with past insistence by Chinese officials that H5N1 exists only in isolated cases in China, and did not necessarily originate there.
The existence of distinct clusters also means the main carriers cannot be wide-ranging birds – instead, most transmission is via local poultry movements. Co-author Malik Peiris, of the University of Hong Kong, told New Scientist: "If there had been repeated waves of virus introduced into, example, Yunnan, one would expect multiple sub-lineages of the virus. But in each place there is only one."
Long distance transmission
But wild birds are involved. The team found H5N1 in six apparently-healthy migratory ducks at Poyang Lake in Jiangxi province, which borders Guangdong and Hunan, in January and March 2005, before the northward migration. The isolates had all the genes, and certain specific mutations, later found in geese at Qinghai Lake, 1700 kilometres northwest. And this virus, notes Peiris, is very like H5N1 in Turkey.
The team also tested whether the Poyang viruses would make ducks too sick to fly by infecting young mallards. "Most got a bit sick then recovered," says Webster, and all shed virus for up to a week. "The evidence is now overwhelming that migrating birds can move H5N1 over long distances," says Peiris. "But they are not the scapegoats for maintaining H5N1 within poultry. There the cause and solution lies within the poultry industry.'
Another important finding of the research is that antibodies to each sub-lineage of H5N1 did not bind readily to other sub-lineages. That means vaccinating people or birds against one strain may not protect against others. The team warns that H5N1 pandemic vaccines should be developed using several strains, and constantly updated.
But to head off the threat of a human pandemic, the authors insist "the source of the virus in southern China must be contained". Webster adds: "Let's be optimistic that [the Chinese authorities] will accept that this thing is out there. It is terribly important to realise that perfectly healthy looking birds have this d**n
virus."
Journal reference: Proceedings of the National Academy of Sciences (DOI:10.1073/pnas.0511120103)
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