| Background
The highly pathogenic H5N1 influenza virus has become endemic in
poultry in Southeast Asia since 2003 and causes a major pandemic
threat to humans.
In the past, H5N1 virus was found in dead wild birds, usually
within flight range of infected poultry farms. On 30 April 2005,
a first outbreak was however detected in bar-headed geese as well
as brown-headed gulls, great black-headed gulls and great cormorants
at Qinghai Lake in western China, which is a protected nature reserve
with no poultry farms in the vicinity. Clinical findings included
paralysis, unusual head tilt, staggering and neck thrill X all
are known features of H5N1 disease in waterfowl. By 4 May, bird
mortality was more than 100 a day; by 20 May, the outbreak rapidly
spread to other islets, with some 1,500 birds dead.
Researchers at the Joint Influenza Research Centre of Shantou
University and the University of Hong Kong put tremendous efforts
to unveil disease caused by H5N1 and transmission of the virus
among migratory geese population in western China.
The Joint Influenza Research Center was established in 2001 by
Shantou University and The University of Hong Kong.
The research findings were published in the top international
scientific journal V NATURE Magazine on 7 July 2005. It is believed
that this outbreak may help to spread the virus over and beyond
the Himalayas and has important implications for developing control
strategies.
Research Method
It was found that 90% of the dead birds were bar-headed geese,
with the remainder being brown-headed gulls and great black-headed
gulls. The researchers isolated 28 H5N1 viruses from 92 cloacal,
tracheal and faecal swabs from the 3 species, and a further 5
viruses from tissue samples from the geese. Genetic analysis
methods were
adopted.
Research Findings
Research results suggested:
- The H5N1 viruses were almost identical
across all gene segments;
- The genes of the Qinghai H5N1viruses
were very similar to those isolated from poultry markets in
Fujian, Guangdong, Hunan
and Yunnan provinces during 2005. However, they were clearly
distinguishable
from those that have caused human infection in Thailand and
Vietnam.
Conclusions
Findings showed:
- The virus causing the outbreak at Qinghai Lake
was a single introduction, most probably from poultry in southern
China.
- H5N1 viruses are now being transmitted between migratory
birds at the lake. The viruses might also move to other migratory
species that act as carriers, remaining highly pathogenic
for domestic
chickens, animals and possibly humans after rapid mutations.
There is a danger that the virus might be carried along the birds
winter migration routes to densely populated areas in the south
Asian subcontinent, a region that seems free of this virus, and
spread as new strains along migratory flyways linked to Europe,
thereby vastly expanding the geographical distribution of H5N1;
therefore, increased surveillance of poultry is called for because
previous experience has shown that control measures become almost
impossible once the virus is entrenched in poultry populations
to prevent large scale outbreak.
To view the full Nature paper, please visit the website at: www.hku.hk/facmed/press.
July 7, 2005
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