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Tuesday, 25 April 2006 |
No need to cull wild birds to stop birdflu: expert
Ducks and other wild birds are carrying the feared H5N1 virus, but
there is no need to cull or otherwise target them as part of efforts to
control the virus, experts said on Thursday.
Poultry are more important carriers of the virus, and H5N1 avian
influenza has probably been circulating, unseen and steadily, for years
in Southeast Asian flocks, the experts in the Netherlands and Sweden
said.
"With our current limited knowledge on highly pathogenic avian
influenza in wild birds, there is no solid basis for including wild
birds in control strategies beyond the physical separation of poultry
from wild birds," Ron Fouchier and Albert Osterhaus of Erasmus Medical
Center in Rotterdam and a team of colleagues wrote in a report
published in the journal Science.
"Even in areas with significant outbreaks in poultry, virus prevalence
in wild birds is low, and the role of these wild birds in spreading the
disease is unclear," they wrote.
"However, there is at present no scientific basis for culling wild
birds to control the outbreaks and their spread, and this is further
highly undesirable from a conservationist perspective," they added.
The H5N1 bird flu virus has spread quickly in recent months, and has
been reported in birds in more than 40 countries across Asia, Europe
and parts of Africa.
Humans rarely catch the virus, but it has killed 110 people and
infected 196 since 2003. Experts fear the virus could acquire the
ability to pass easily from human to human and could kill millions of
people in a pandemic.
The virus is found naturally in ducks, and usually does not make them
sick. But they can spread it, especially in their droppings.
"It has been shown that influenza viruses remain infectious in lake
water up to 4 days at 22 degrees C (72 degrees F) and more than 30 days
at 0 degrees C (32 degrees F) (7)," the researchers wrote.
DABBLING IN DISEASE
Dabbling ducks -- those that prefer to browse in shallow waters, such
as mallards -- are particularly likely to carry the virus with no ill
effects.
When chickens and ducks are allowed to mingle, chickens can become infected and H5N1 kills them very quickly.
Veterinarians and other animal-health experts say quick culling of
poultry is the best way to deal with this, but there has been some
debate about the role of wild birds.
"It is clear that the H5N1 problem originated from outbreaks in poultry
and that the outbreaks and their geographical spread probably cannot be
stopped without implementation of proper control measures in the global
poultry industry," Fouchier's team wrote.
"Poultry trade and mechanical movement of infected materials are likely
modes for spreading highly pathogenic avian influenza in general," they
added.
"It is most likely that the H5N1 virus has circulated continuously in
domestic birds in Southeast Asia since 1997 and, as a consequence, has
evolved substantially," they wrote.
Something must have changed, experts agree. H5N1 has been around in
birds since 1959 and a 1997 outbreak in Hong Kong, in which 18 people
became infected, was quickly stopped with merciless culling and
disinfection of bird markets.
But it re-emerged in 2003 and has accelerated its spread.
The experts suggested that the spring migration may not spread the
virus much. Water fowl seem most susceptible to infection when they are
young, and they cited studies showing that the viruses are more common
in birds in the autumn and less common in the spring.
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