-----Original Message-----
From: WHO Epidemiological Bulletin [mailto:WER-REH@xxxxxxx]
On Behalf Of Editor Of List
Sent: Friday, August 20, 2004 9:30 AM
To: WER-REH@xxxxxxx
Subject: World Health Organziation - Weekly Epidemiological Record
Weekly Epidimiological Record
Full Issues available at: http://www.who.int/wer
Contents of this weeks's issue:
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20 AUGUST 2004, 79th YEAR
No. 34, 2004, 79, 309-312
Contents
309 Human cases of avian influenza: situation in VietNam as
of 18 August
2004
310 Onchocerciasis (river blindness) Report from the thirteenth
InterAmerican Conference on Onchocerciasis,
Cartagena de Indias, Colombia
312 International Health Regulations
____________________________
Disease Outbreak News Item(s)published on the World Wide Web
http://www.who.int/csr/don
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Avian influenza: H5N1 detected in pigs in China
20 August 2004
A researcher from China's Harbin Veterinary Research
Institute has today
presented initial evidence that pigs from farms in parts of
China have been
infected with the H5N1 strain of avian influenza. The
findings, set out in a
table and without further supporting data, were presented today at an
international symposium on SARS and avian influenza held in Beijing.
WHO has requested confirmation and further details about this study.
Pigs are known to be susceptible to infection with avian
influenza viruses.
However, natural infection of pigs with the H5N1 strain has not been
previously reported.
In order to assess the implications for human health, it is
important to
know whether the reported infections in pigs are rare events, possibly
caused by contact between pigs and wild birds. Wild aquatic
birds, which are
the natural reservoir of all influenza viruses, can carry the
H5N1 strain
without developing symptoms, and are known to excrete large
quantities of
the virus in their faeces.
A comparison of the H5N1 strain isolated in pigs with strains recently
circulating in poultry populations in parts of Asia is needed
to determine
whether the virus is being passed directly from poultry to
pigs. Evidence of
direct transmission of H5N1 from poultry to large numbers of
pigs would be
of particular concern, as this would increase opportunities for a new
influenza virus with pandemic potential to emerge.
Pigs have been implicated in the emergence of new influenza viruses
responsible for two of the previous century's influenza
pandemics. Pigs have
receptors in their respiratory tract that make them
susceptible to infection
with human and avian influenza viruses. If a pig is
simultaneously infected
with both a human and an avian influenza virus, it can serve
as a "mixing
vessel", facilitating the exchange of genetic material between the two
viruses in a process known as "reassortment". The resulting
new virus, which
will not be recognized by the human immune system, will have pandemic
potential if it retains sufficient human genes to allow efficient
human-to-human transmission, and if it causes severe disease
in humans.
Confirmation of H5N1 infection in pigs would add complexity to the
epidemiology of this disease, but needs to be viewed in
perspective. During
the peak of the poultry outbreak of H5N1 in Viet Nam earlier
this year,
extensive testing of pigs on farms where poultry were heavily infected
failed to find evidence of infection in pigs. In addition, Hong Kong
authorities regularly perform random testing for the H5 avian
influenza
virus subtype in pigs imported from mainland China. No
infection in pigs has
been detected to date.
WHO, in collaboration with FAO and OIE, will be assessing the
implications
of reported H5N1 infection in pigs as further details become
available.
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