- An outbreak of avian flu in wild geese in western China
has raised fears that the virus responsible could soon spread beyond its
Asian stronghold.
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- Researchers say evidence of the H5N1 pathogen in the
geese is a big concern because of the migratory animals' ability to fly
huge distances.
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- Their reports, in the Science and Nature journals, are
the first to show viral transmission between wild birds.
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- Previously, the flu was only seen to move to wild birds
from domestic fowl.
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- World health officials are worried avian influenza virus
(AVI) could cause a pandemic of human disease if it ever acquires the ability
to pass easily from human to human.
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- So far, the impact on people has been limited to 54 deaths
out of 154 infections in Vietnam, Thailand and Cambodia - again, after
contact with domesticated chickens and other infected food birds.
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- News that the H5N1 viral strain is now being passed around
wild geese makes avian flu even more of a global threat than it already
is, the scientists say.
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- "These birds can fly one thousand miles a day at
maximum," explained Yi Guan, of the University of Hong Kong, China.
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- "This means the virus has the opportunity to expand
its distribution to currently virus-free areas," he told BBC News.
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- Global threat
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- The reported outbreak was first detected on 30 April
in bar-headed geese ( Anser indicus ) at Lake Qinghai, a protected nature
reserve in Qinghai Province.
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- The animals displayed classic symptoms, such as tremors,
diarrhoea, head tilt and paralysis.
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- By 20 May, the outbreak had claimed some 1,500 birds,
report Yi Guan and colleagues in Nature; not just bar-headed geese, but
great black-headed gulls ( Larus ichthyaetus ) and brown-headed gulls (
Larus brunnicephalus ).
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- Genetic analysis of the virus extracted from dead birds
shows that it is closely related to the strain that has caused human illness
in Thailand and Vietnam.
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- Lake Qinghai is a major breeding centre for migrant birds,
say to Jinhua Liu and colleagues in Science magazine. Bar-headed geese
are known to move south to Burma and north over the Himalayas to India.
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- In their report, Liu's team analysed a variety of birds
collected from the lake. The scientists managed to isolate four H5N1 virus
sub-strains, and tests on mice and chickens showed them to be highly virulent.
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- Fifteen of the 16 test animals were dead within three
days of exposure.
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- "The occurrence of highly pathogenic H5N1 AIV infection
in migrant waterfowl indicates that this virus has the potential to be
a global threat," Liu's team write in Science.
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- Evidence of spread in wild geese means farmers outside
of southeast Asia should now be more vigilant for signs of the disease,
the research teams say. Avian flu is almost impossible to stamp out once
it becomes established in farm poultry populations, they warn.
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- H5N1 BIRD FLU VIRUS * Principally an avian disease, first
seen in humans in Hong Kong, 1997 * Almost all human cases thought to be
contracted from birds * Isolated cases of human-to-human transmission in
Hong Kong and Vietnam, but none confirmed
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- © BBC MMV
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- http://news.bbc.co.uk/2/hi/science/nature/4657145.stm
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