from Taichi Kato, an ornithologist in Japan:
This news in Science magazine adequately summarizes the most up-to-date
facts and discussions in the role of migratory birds potentially spreading
the current H5N1 HPAI. If you can access to the online journal, make a
visit at http://www.sciencemag.org/cgi/content/full/310/5747/426 .
“Are Wild Birds to Blame?”
Dennis Normile
Science 21 October 2005: 426-428.
[Some excerpts and comments]
As H5N1 reaches Europe, scientists debate the role of wild birds but agree
on the need for greater surveillance
But avian experts have been almost universally skeptical that wild birds are
spreading the virus. One reason is that sampling of tens of thousands of birds
has failed to turn up a single healthy wild bird carrying the pathogenic
strain of H5N1,
-> No direct evidence of carrying H5N1.
Evidence so far suggests that H5N1 kills wild ducks and geese nearly as
efficiently as it does chickens. “Dead ducks don’t fly” has been the refrain,
as avian experts point out that sick and dying birds simply can’t spread
viruses very far. Instead, epidemiologists investigating the virus’s jump,
even to geographically far-flung regions, keep turning up evidence suggesting
that the poultry trade and other human activities are responsible.
-> This statement is slightly a bit different from the recent WHO/OIE
fact summaries. They consider that H5N1 is less pathogenic to
migratory ducks and geese. I suspect that this WHO/OIE statement
is a precautionary one (to prepare the worst case) rather than
evidence-based analysis.
Now, however, evidence implicating wild birds is starting to convince even
some of the doubters. “Until about 2 months ago, I was pretty skeptical on
whether wild birds were playing a role,” says David Suarez, a virologist with
the U.S. Department of Agriculture’s (USDA’s) Southeast Poultry Research
Laboratory
What changed his mind, he says, was the death of 100 or so ducks, gulls,
geese, and swans from H5N1 at a remote lake in Mongolia that he believes
can’t be explained by human activities. And, he and others add, in an
unexpected twist, it’s beginning to look as though the culprits might not
be the long-suspected migratory waterfowl but another yet-unidentified wild
species.
-> This indicates that (even in the presence of European findings),
at least some epidemiologists consider the Mongolian cases most compelling.
[This is the same reason why I have been following the Mongolian case
in depth]. There must have been a far greater chance of human and poultry
contacts in crowded Europe than in Mongolia. There have even been a report
of poultry meat seized from Turkey even after the ban of poultry trade
from Turkey. In relation to the second suspected occurrence in Turkey,
the local media reported the presence of live chicken movements from the
region of the initial outbreak, sufficient to suspect the presence of
routine trade activities.
Nailing down the answer became even more urgent last week with the
confirmation that H5N1 has now entered Europe.
Everyone recognizes that if wild birds are involved, new strategies will be
needed to halt the virus’s spread to domestic flocks–and from them to people.
A growing number of scientists and organizations are calling for dramatically
increased global surveillance to profile all viruses circulating in wild
birds.
-> This is the true reason why European cases are so weighed; these
cases are not “better proofs” of transmission by migratory birds, but
are an alarm to the global community to face the problem as a serious
threat: all nations need to make a surveilance network of wild birds
and poultry, and there is an urgent need of international cooperation
for funding. The FAO and OIE statement, however, has been regarded as
fear by the public against wild birds…
So far, however, there is no known natural reservoir for highly pathogenic
avian influenza viruses. They emerge only after low-pathogenicity viruses
jump from water birds into chickens and turkeys.
-> We always need to stress that LPAI (natural strain) and HPAI have
different characteristics in the wildlife.
No one has yet uncovered the lineage of the highly pathogenic H5N1 strain now
endemic in Asia. Presumably, it evolved from a low-pathogenicity H5N1 variant
circulating in waterfowl in southern China before the first known outbreak of
the disease in chickens in Hong Kong in 1997.
-> This information is precious for those who have been searching for
an ancestral strain of the current H5N1 HPAI: the answer is “not discovered
yet”.
When public health experts pointed to migratory birds as a likely source,
ornithologists and animal epidemiologists showed that the outbreaks did not
neatly fit any known migratory patterns. If migratory birds were carriers,
they argued, the virus should have turned up in the Philippines and Taiwan
by now, but it hasn’t.
-> This also explains why health officials (including WHO’s Lee, the
biotechnology company such as Recombinomics) usually stress on wild birds.
The more the possibilty of a pandemic is spoken, the more health officials
(rather than wildlife researchers) are asked to make a public statement,
likely addressing on migratory birds.
-> The recent discovery of H5N1 in smuggled birds in Taiwan is a notifiable
feat, since if a secondary outbreak may have arisen, that would have easily
been identified as the most compelling evidence of migratory birds
transmitting the virus (since migration is already in place).
What’s more, since the late 1990s, USDA has sampled more than 10,000 waterfowl
crossing the Bering Sea from Asia to Alaska, while University of Hong Kong
researchers have tested several thousand entering Hong Kong; neither group
has found a single healthy bird carrying the H5N1 virus.
-> Accumulating negative data.
Instead, human movements of infected poultry have spread the virus over
seemingly improbable distances. For instance, an outbreak of H5N1 among
poultry in Lhasa, Tibet, in January 2004 was traced to a shipment of chickens
from Lanzhou in China’s Gansu Province, about 1500 kilometers away. An even
more bizarre case surfaced in October 2004, when an air traveler was caught
at Brussels Airport with two crested hawk eagles, infected with H5N1, in his
carry-on bag. The smuggler had bought them at a Bangkok bird market on behalf
of a Belgian falconer.
-> Perhaps this would clarify the Lhasa case (which people would have
concerned about). Lanzhou is located not very far away from Qinghai lake
(any relation between them?).
More explanation about Qinghai case:
The die-off immediately raised alarms that surviving birds might carry the
virus to India and beyond. But, apparently because of infighting between
Chinese ministries and institutions, the government barred Chinese and outside
scientists from sampling or tracking the travel of surviving birds.
“It was a missed opportunity,”
Researchers are still wondering how the virus got to this remote corner of
China. Just after the Lake Qinghai outbreak, the virus turned up on a poultry
farm in the same province. This “makes it difficult to tell whether poultry
or wild birds brought the virus to the area,” says Suarez.
at Erkhel Lake. The group collected 774 samples from both dead and living
birds. USDA confirmed highly pathogenic H5N1 in dead birds–but found no
evidence of the virus in any samples from the live ducks, gulls, geese,
or swans.
is that wild birds carried the virus to Erkhel Lake and infected the birds
that eventually died. “We don’t know which species were responsible for
spreading the virus,”
Figuring out which species might be involved will be tough, others note,
as next to nothing is known about avian influenza except in waterfowl.
Chinese Academy of Sciences (CAS). Since last March, he has collected more
than 6000 viral and serological samples from a variety of wild animals
throughout China, including 2000 samples from migratory and resident birds,
and is searching for H5N1.
George Gao, a virologist at CAS’s Institute of Microbiology in Beijing, has
collected several dozen serum samples from birds that survived the H5N1
outbreak at Qinghai Lake. If any test positive for antibodies to the H5N1
virus, says Gao, who is preparing to publish a paper, it would suggest that
some mildly infected water birds might be carrying the virus long distances.
-> This indicates (at least up to now) that no “virus positive” healthy
migratory bird was discovered after the outbreak at Qinghai Lake, pending
the publication of the mentioned work.