Published Date: 2004-02-15 23:50:00
Subject: PRO/AH> Avian influenza, poultry vaccines (05)
Archive Number: 20040215.0501
AVIAN INFLUENZA, POULTRY VACCINES (05)
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A ProMED-mail post
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Date: Sat,14 Feb 2004
From: ProMED-mail <promed@promedmail.org>
Source: NewScientist.Com, 11 Feb 2004 [edited]
<http://www.newscientist.com/news/print.jsp?id=ns99994670>
Genetic analysis probes bird flu's history
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Scientists analysing the genetic sequence of the H5N1 flu virus that killed
a person in Vietnam say it is highly similar to sequences isolated recently
from ducks and geese in China. They are careful to warn that this does not
necessarily prove that the avian influenza epidemic currently raging across
east Asia started in China. But the new analyses do show that this kind of
H5N1 virus has been circulating widely in the region over the past several
years.
Recent work also reveals that the virus has been mutating rapidly in
response to "unusual selective pressure" from an unknown source. Prominent
virologists have warned that widespread vaccination of poultry against bird
flu -- as has been the case in China -- could have this effect.
Earl Brown, a flu virologist at the University of Ottawa in Canada,
compared the genetic sequence of the virus isolated from a Vietnamese
person who died of bird flu in January 2004 to other gene sequences using a
program called "BLAST". This assesses the degree of similarity in the
nucleotide sequences posted to a centralised computer database, Genbank. He
compared all 8 genetic strands from the Vietnamese virus with every other
sequence in the database.
The ones that matched closest all came recently from poultry from China. 5
of the 8 strands were 96 to 99 per cent identical to an H5N1 flu virus
found in duck meat smuggled from eastern China and intercepted in Taiwan in
2003.
The remaining 3 were 98 per cent the same as sequences obtained from a
goose in Hong Kong in 2000. Geese and ducks in Hong Kong are imported from
large, intensive poultry producers in Guangdong province, China. "This
shows that this virus has been in China recently, and it has the scars to
prove it," Brown told New Scientist.
Other scientists have found similar relationships among bird flu viruses in
the region. Researchers from Japan's National Institute of Animal Health
told journalists recently they had found that the Viet Nam virus, the virus
that caused an outbreak of bird flu in Japan in January 2004 and a goose
virus from Guangdong in 1996 were all closely related. The Japanese
researchers also said that the gene for the major surface protein in the
virus that caused the Japanese outbreak was 97 per cent identical to the
same gene in the virus that in 2003 killed a Hong Kong man who had just
travelled to southern China.
Flu virologist Richard Webby, of St Jude's Children's Research Hospital in
Memphis, Tennessee, sounds a note of caution. He points out that there are
no virus sequences from elsewhere in east Asia, partly because until
recently all affected countries denied having bird flu."So just because
this virus is similar to Chinese samples we can't say this particular
outbreak started there, because we have no samples from anywhere else," he
says.
The scientific literature describes a number of H5N1 flu viruses
circulating in poultry in southeastern China since 1996. However, Webby
points out that, although these viruses have been closely related, there
has been a sharp increase in their genetic diversity since 2001.
The major surface protein on the virus that killed 6 people in Hong Kong in
1997 was different from the one on the lethal human infection in 2003.
"Everyone was surprised by that," Webby told New Scientist, but now the
Viet Nam virus protein "is very different again. "Other genes are diverging
too, he says. "We have a bucket of evolution going on. This shows that H5
is circulating fairly widely somewhere, under some kind of unusual
selective pressure."
The explosion in variation coincides with the period during which Chinese
farmers have practiced widespread vaccination of chickens against flu.
In 2003, scientists who developed an improved flu vaccine for poultry,
including Robert Webster of St Jude's, concluded that such vaccination "may
be a serious problem for human pandemic preparedness" (Virology vol 314,
p580). Such vaccines, they wrote, might mask disease signs while allowing
the birds to continue to shed virus. In such a case, "persistence of virus
infection in the presence of a flock immunity may contribute to increased
virus evolution".
[byline: Debora MacKenzie]
--
ProMED-mail
<promed@promedmail.org>
[ProMED-mail has been requesting information on the characteristics of the
HPAI vaccines officially in use in China since 2002, and -- as recently
revealed -- also applied in Indonesia and (probably and informally) in
other countries in the region (see commentary in postings 20040131.0380,
20040205.0421, 20040206.0430, 20040208.0448, 20040211.0462). We maintain
our sincere hope that such important information will be forthcoming.
The Chinese Bureau of Animal Husbandry and Health in the Ministry of
Agriculture has recently provided to the international community valuable,
official, detailed information -- followed by updates -- on the currently
prevailing HPAI disease situation in this huge country. This reflects a
commendable expression of transparency. It will be very helpful if future
reports will include information on the extent, timing, and nature of the
routine HPAI vaccination practiced on large commercial poultry farms in
southern China. - Mod.AS]
See Also
Avian influenza, poultry vaccines (04) 20040211.0462Avian influenza - poultry vaccines (03) 20040208.0448
Avian influenza - Eastern Asia (20) 20040206.0430
Avian influenza - Eastern Asia (18) 20040205.0421
Avian influenza - Eastern Asia (16) 20040131.0380
Avian influenza, poultry vaccines (02) 20040129.0339
Avian influenza, poultry vaccines 20040128.0330
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