xperts warn of bird flu's human threat
February 21, 2006 - 6:24AM
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Bird flu is likely to cross over into people again and
again if it even once acquires the ability to pass from human to human,
experts have warned.
In theory, the virus only has to mutate
once, in one person, to spark a pandemic. But the researchers argue
that this could happen again and again, in several places around the
world.
They said even if the current pandemic killing birds
passes, no one should breathe a sign of relief because the threat to
people will not be gone.
"At best, a containment policy will only
postpone the emergence of a pandemic, 'buying time' to prepare for its
effects," Dr Marc Lipsitch and colleagues from the Harvard School of
Public Health and Dr Carl Bergstrom from the University of Washington
wrote.
This is what officials hope they are doing now by culling
birds when new outbreaks of H5N1 avian influenza occur. Public health
experts agree the world is nowhere near ready to cope with a pandemic,
but with a few years' preparations, some countries might be.
"We
argue here that if a single introduction of a pandemic-capable strain
is expected, multiple introductions should also be expected,"
Lipsitch's team wrote in the Public Library of Science Medicine, an
online medical journal.
"Each containment effort would likely be
more difficult than the last as manpower, antiviral stockpiles, and
other scarce resources become depleted," they wrote.
H5N1 avian
influenza has spread in chickens from Korea, across China, south into
Indonesia, west across Turkey into western Europe and into the African
continent.
It has killed or forced the culling of more than 200
million birds in 32 countries and Hong Kong. While it does not easily
infect people yet, it has affected 170 people and killed 92, according
to the latest World Health Organisation figures.
No one can say
if or when it would happen, but if H5N1 acquired the ability to pass
easily from human to human, it could spark a pandemic that would kill
millions or even tens of millions within a few short months.
Some
experts have published theoretical models showing that quick action
with antiviral drugs, culling of birds and isolation of cases could
quell such a pandemic before it started.
But it would require a
lot of luck, noted Lipsitch and colleagues - not the least identifying
those cases right away, before they spread the disease.
Other
experts have also noted this and also said there is no reason to
believe that the mutations needed to make H5N1 a human disease would
occur only once. Lipsitch's team ran some mathematical models based on
known disease outbreaks.
Their article suggests that an H5N1
pandemic could only be contained temporarily. And the longer the virus
is around, the harder it will be to stop it from spreading.
"Even
if each successive containment effort is no more difficult than its
predecessor, the chance of at least one failure increases with the
number of introductions," they wrote.
"Since the last pandemic
nearly 40 years ago, we have observed dramatic changes in social and
ecological factors thought to facilitate emergence of a
pandemic-capable strain," the researchers wrote.
"Surging human
and bird populations in Asia have increased the frequency of contact
between birds and humans - and these changes might facilitate emergence
by permitting 'crossing over' of a mutated avian influenza to humans,
or by allowing human and avian influenzas to reassert in the same
animal host."
© 2006
AAP
http://www.theage.com.au/news/World/Experts-warn-of-bird-flu s-human-threat/2006/02/21/1140284028209.html
If I'm reading
this one right, the implications are that this is just the beginning of
something that is not restricted to two or three waves as we have been
posting. A new disease ridden era?
Edited by wannago