Migrating birds didn't cary avian flu

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The New York Times

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May 11, 2006

Migrating Birds Didn't Carry Flu

By ELISABETH ROSENTHAL

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Last week, the Netherlands and Switzerland rescinded mandates that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 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. "

Meryl Nass, MD

Mount Desert Island Hospital

Bar Harbor, Maine 04609

207 288-5081 ext. 220