|
|
Migrating Birds Didn't Carry Flu
By ELISABETH ROSENTHAL
Published: May 11, 2006
http://www.nytimes.com/2006/05/11/world/europe/11birdflu.html?_r=2&th&emc=th&oref=slogin&oref=login
ROME, May 10 — Defying the dire predictions of health officials, the flocks
of migratory birds that flew south to Africa last fall, then back over
Europe in recent weeks did not carry the deadly bird flu virus or spread it
during their annual journey, scientists have concluded.
International health officials had feared that the disease was likely to
spread to Africa during the southward migration and return to Europe with a
vengeance during the reverse migration this spring. That has not happened —
a significant finding for Europe, because it is far easier to monitor a
virus that exists domestically on farms but not in the wild. "It is quiet
now in terms of cases, which is contrary to what many people had expected,"
said Ward Hagemeijer, a bird flu specialist with Wetlands International, an
environmental group based in the Netherlands that studies migratory birds.
In thousands of samples collected in Africa this winter, the bird flu virus,
A(H5N1), was not detected in a single wild bird, health officials and
scientists said. In Europe, only a few cases have been detected in wild
birds since April 1, at the height of the migration north.
The number of cases in Europe has fallen off so steeply compared with
February, when dozens of new cases were found daily, that specialists
contend that the northward spring migration played no role. The flu was
found in one grebe in Denmark on April 28 — the last case discovered — and a
falcon in Germany and a few swans in France, said the World Organization for
Animal Health, based in Paris.
In response to the good news, agriculture officials in many European
countries are lifting restrictions intended to protect valuable poultry from
infected wild birds.
Last week, the Netherlands and Switzerland rescinded mandates that poultry
be kept indoors. Austria has loosened similar regulations, and France is
considering doing so. The cases in Europe in February were attributed to
infected wild birds that traveled west to avoid severe cold in Russia and
Central Asia but apparently never carried the virus to Africa. The
international scientists who had issued the earlier warnings are perplexed,
unsure if their precautions — like intensive surveillance and eliminating
contact between poultry and wild birds — helped defuse a time bomb or if
nature simply granted a reprieve.
"Is it like Y2K, where also nothing happened?" asked Juan Lubroth, a senior
veterinary official at the United Nations Food and Agriculture Organization
in Rome, referring to the expected computer failures that did not
materialize as 1999 turned to 2000. "Perhaps it is because it was not as bad
as we feared, or perhaps it is because people took the right measures."
Still, he and others say, the lack of wild bird cases in Europe only
underscores how little is understood about the virus. And scientists warn
that it could return to Europe.
"Maybe we will be lucky and this virus will just die out in the wild," Mr.
Lubroth said. "But maybe it will come back strong next year. We just don't
have the answers."
The feared A(H5N1) bird flu virus does not now spread among humans, although
scientists are worried it may acquire that ability through natural
processes, setting off a worldwide pandemic. The less bird flu is present in
nature and domestically on farms, the less likely it is for such an
evolution to occur, they say.
Worldwide, bird flu has killed about 200 humans, almost all of whom were in
extremely close contact with sick birds.
Specialists from Wetlands International, who were deputized by the Food and
Agriculture Organization, sampled 7,500 African wild birds last winter in a
search for the disease. They found no A(H5N1), Mr. Hagemeijer said, so it is
not surprising that it did not return to Europe with the spring migration.
While bird flu has become a huge problem in poultry on farms in a few
African countries, including Egypt, Nigeria and Sudan, specialists
increasingly suspect that it was introduced in those countries through
imported infected poultry and poultry products. Mr. Hagemeijer said the
strength of the virus among wild birds possibly weakened as the southward
migration season progressed, a trait he said was common in less dangerous
bird flu viruses. That probably limited its spread in Africa, he said.
A(H5N1) is the most deadly of a large family of bird flu viruses, most of
which produce only minor illness in birds.
Many bird flu viruses are picked up by migratory birds in their nesting
places in northern lakes during the summer and fall breeding season. As the
months pass, the viruses show a decreasing pattern of spread and
contamination.
"So it tends to be mostly a north-to-south spread, and then it wanes," Mr.
Hagemeijer said.
Still, this means that the cycle could start again this summer, if the virus
— which can live for long periods in water — has persisted in those breeding
areas. Many bird specialists contend that a small number of wetland lakes in
Central Asia and Russia may harbor the virus all the time, serving as the
origin of European and Central Asian infections.
Scientists still do not know which birds carry the virus silently and which
die from it quickly, or how it typically spreads from wild bird to wild
bird, or between wild birds and poultry.
Farm-based outbreaks of bird flu still occur constantly in a number of
countries, although not in Europe. Ivory Coast had its first outbreak of
bird flu, on a farm, last week.
But other countries, like Turkey, have made substantial progress in
containing the disease among poultry, Mr. Lubroth said. He added that he
hoped that quick measures to limit outbreaks had reduced the virus's spread
in Africa.
After the virus was found on farms in Nigeria in January, many specialists
expected it to spread rapidly among farms and into wild birds in the region.
Apparently, it did not.
"Why didn't it sweep up the coast from Niger, to Benin and Senegal and back
up through Europe? Why didn't it hit Africa's big lakes?" Mr. Lubroth asked.
"All we have are a few snapshots of the virus. What we need is a movie of
its life cycle."
|
|
|