| (July 8, 2004XBeijing and Shantou)
The Joint Influenza Research Centre (Shantou University Medical College/Hong
Kong University) has published a study that shows H5N1, the highly
pathogenic avian influenza virus, has become endemic in China and
the East Asian region.
Results of the JIRC's extensive 5-year study of the virus were
published in Nature #431. The study showed that the H5N1 viruses
are not easily eradicable, and pose a threat to public and veterinary
health in the region and potentially the world. The JIRC suggested
that governments implement sustainable control measures to reduce
the frequency of H5N1 outbreaks and the probability of human infection.
To trace the ecological genetic origins of these outbreaks, the
investigators compared H5N1 viruses isolated from poultry in Indonesia,
Thailand and Vietnam as well as from humans in Thailand and Vietnam
with H5N1 isolates obtained during prospective surveillance of live
poultry markets in Hong Kong and in Guangdong, Hunan and Yunnan
provinces from 2000 to 2004. Since 2001, H5N1 viruses have continued
to surface in mainland China with a seasonal pattern, peaking from
October to March, when the mean temperature falls below 20 degrees
Celsius.
The timing and distribution of the H5N1 infection in poultry in
China since 2001 coincides with the general period of winter bird
migration to southern China. It is unclear whether the H5N1 virus
has become established in wild bird populations. However, the potential
role of wild birds in the circulation of H5N1 viruses must be considered
in control strategies.
H5N1 is now endemic in poultry in Asia and is ecologically entrenched
to present a long-term pandemic threat to humans. At present these
viruses are poorly transmitted from poultry to humans, and there
is no conclusive evidence of human-to-human transmission. However,
continued, long-term human exposure to H5N1 viruses increases the
likelihood that the viruses will acquire the necessary characteristics
for efficient human-to-human transmission through genetic mutation
or reassortment with a prevailing human influenza A virus.
Although other countries in the East Asian region have been affected,
Hong Kong has implemented effective preventive measures and has
remained remarkably free of H5N1 outbreaks in poultry in 2004.
The JIRC is supported by the Li Ka Shing Foundation and headed
by Dr. K.S. Li and Dr. Y. Guan.
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