Wild birds are the ultimate
source of all avian flu's - but that,
scientists argue, does not mean that they
are important in spreading the current virus
or should be wiped out to stop it.
Scientists searching for the roots of the
A(H5N1) virus that is threatening to turn
into a human pandemic consider live bird markets,
traveling poultry workers and the movement
of domestic poultry and fighting cocks more
likely vectors for spreading the disease from
country to country and from farm to farm.
Wherever the strain originated, it has been
surviving and mutating in domestic flocks
for years, scientists said.
By Donald G. McNeil Jr in
the New York Times (Volkskrant 16-10-2004)
Migrating birds are the source of all bird
flu's but are not known to be spreading
the new, virulent strain Scientists believe
close-packed birds in markets and on farms
and fighting cocks are bigger problems.
Killing wild birds is the wrong response
to Poultry workers and markets are often
culprits in an outbreak.
The issue became important early
this year, when some Asian health officials
accused migratory birds of spreading the flu
and threatened to attack them with the same
lethal vigor that has been applied to domestic
chickens. For a brief period in July, Thai
officials killed open-billed storks and chopped
down the trees they nested in. Singapore officials
publicly - and rather fantastically- discussed
killing crows and mynahs, which do not migrate,
and netting wild birds to clip their wings.
The gates of nature reserves in several countries
were closed and people were warned to shun
wild birds. In Vietnam, panic led to the release
of many pets, which were seen roosting in
city trees.
"I've never seen anything like it,"
said Colin Poole, Asia director for the Wildlife
Conservation Society, which runs the Bronx
Zoo in New York and animal protection programs
around the globe. "Birds had become the
enemy".
In fact, scientists said, most ways the flu
can move depend on humans. In "wet markets",
dozens of birds are penned together. Poultry
workers' boots and truck tires can track infected
feces long distances.
Fighting roosters are frequently carried long
distances to bouts where thousands of dollars
may be bet on them. When restrictions are
imposed, they have been smuggled, even crossing
borders hidden in hubcaps of cars, one doctor
said.
"We don't have indications that wildlife
are major players" in the current outbreak,
said Dr Juan Lubroth, senior officer of the
infectious disease group at the Food and Agriculture
Organization of the United Nations.
The genes of all strains of avian flus can
be found in wild waterbirds. In the Arctic,
where many spend their summers, viruses "get
mixed up in the ponds like soup, and survive
even when they freeze", said Dr. William
Karesh, director of field veterinarians for
the Wildlife Conservation Society. "The
mixing and matching has been going on for
thousands of years".
Theoretically, they could be vectors for spreading
the disease to new continents, because Asian
and American birds share pools in Siberia
and Alaska and sometimes switch flyways, said
Dr Richard Veit, an ornithologist at the
College of Staten Island. Pintail ducks banded
in Asia have been shot in North America and
vice versa, he said. Some shorebirds, like
sanderlings, migrate as far as New Zealand
and Chile.
That, however, is not considered a likely
transmission route.
If a very lethal strain emerged in the Arctic,
it would probably die out there. "Dead
birds don't fly far", said Dr. Carol
Cardona, a poultry veterinarian at the University
of California at Davis.
Wild birds have sometimes been unfairly blamed.
Poultry farmers singled out cattle egrets
for a California flu outbreak, "but the
egrets were negative - it was the egg flats
being trucked from farm to farm without being
cleaned", Dr. Cardona noted.
Although Asian newspapers have quoted government
officials saying that thousands of wild birds
would be tested, few results have been released,
Mr. Poole said. A friend in the Thai government,
he said, told him the storks killed there
were negative.
Mr. Poole said he could find only seven birds
of six species that were confirmed positive
for the A (H5N1) strain, all in Hong Kong:
a black headed gull, two gray herons, a little
egret, a peregrine falcon, a pigeon and a
tree sparrow. The last three were found dead
near infected farms.
"Let's speak in the singular", he
said. "That is a dead migratory bird:
the gull".
(Some falcons also migrate, but not with the
regularity that shorebirds do.)
"The evidence I can find", Mr. Poole
concluded, "is that migratory birds are
not vectors, but victims".
Both he and Dr. Lubroth, speaking at a conference
at Rockefeller University in New York on animal-human
diseases, showed that outbreaks had not followed
flyways or migration schedules.
"There are no waterfowl that winter in
southern China and then go to Vietnam, Cambodia,
Indonesia or central Thailand", said
Mr Poole, who lives in Cambodia.
Dr Lubroth showed that outbreaks appeared
in areas with the largest concentrations of
domestic chickens, pigs and people. (Asia
has seven billion chickens, he said.)
Vaccination is illegal in countries like Thailand
that export many chickens because Europe and
the United States forbid imports from countries
that vaccinate. But China and Indonesia consume
most of their own poultry and allow inoculation.
an epidemic, said Koh Kheng Lian, a professor
of environmental law at the University of
Singapore.
Besides upsetting ecosystems, it can have
unintended consequences. In the 1950's, she
said, Mao urged peasants to kill wild birds
that were eating rice crops. The result was
disastrous because the birds also had kept
rice-eating worms in check.
Dr Lubroth said farms should adopt biosecurity
measures like quarantining newly purchased
birds until they prove healthy, netting farm
ponds to keep wild birds away, and washing
all boots and tires.
Bird handlers have some dangerous habits.
For example, cock handlers suck blood and
mucus from beaks during fights. And Buddhists
hold birds to their faces in prayer before
releasing them.
"If you were thinking of a risk to human
health, this is it", Mr Poole said.
"But as a religious issue, it would be
hard to stop. The king does it every week".
