Bird Flu: Science and Policy

[DewDiligence]

Birds Return to Europe Without Virus

http://www.nytimes.com/2006/05/10/health/10cnd-flu.html

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May 10, 2006
By ELISABETH ROSENTHAL
International Herald Tribune

ROME, May 10 — The flocks of migratory birds that winged their way south to Africa last autumn and then back over Europe in recent weeks did not carry the H5N1 flu virus or spread it during their annual journey, scientists have concluded, defying health officials' dire predictions.

International health officials had feared that the disease was likely to spread to Africa during the winter 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 nature.

"It is quiet now in terms of cases, which is contrary to what many people had expected," said Ward Hagemeijer, an avian influenza specialist with Wetlands International, an environmental group based in the Netherlands that studies migratory birds.

In thousands of samples collected in Africa this winter, H5N1 was not detected in a single wild bird, officials and scientists said. In Europe, there have been only a handful of cases detected in wild birds since April 1, at the height of the northward migration.

The number of cases in Europe has decreased so dramatically compared to February, when dozens of new cases were found daily, that experts believe the northward spring migration played no role. There was one grebe in Denmark on April 28 — the last case — as well as a falcon in Germany and a few swans in France, according to the World Organization for Animal Health, based in Paris.

In response to the good news, agriculture officials in many European countries have this month lifted restrictions designed to protect valuable domestic poultry from infected wild birds.

In the first week in May, both the Netherlands and Switzerland rescinded mandates that poultry be kept indoors. Austria has loosened similar regulation and France is considering doing so, as farmers (and their poultry) chafe under the restrictions of indoor life as the weather warms.

The February cases in Europe were attributed to infected wild birds that traveled west to avoid severe cold in Russia and Central Asia but apparently never carried the virus on to Africa. The international scientists who had issued the prior warnings are perplexed, unsure if their preventive measures — like intensive surveillance and eliminating contact between poultry and wild birds — helped defuse a time bomb, or if nature simply granted the reprieve. And they warn that H5N1 could return to Europe in the future.

"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 as the year 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.

"Maybe we will be lucky and this virus will just die out in the wild," Dr. Lubroth said. "But maybe it will come back strong next year. We just don't have the answers."

…Specialists from Wetlands International, who were deputized by the Food and Agriculture Organization, sampled 7,500 African wild birds last winter in their search for the disease. They found no H5N1, Mr. Hagemeijer said, so it is not surprising that H5N1 did not return to Europe with the spring migration.

While avian influenza has become a huge problem in domestic poultry on farms in a few African countries, like Egypt, Nigeria and Sudan, experts increasingly suspect that it was introduced there through imported infected poultry and poultry products.

Mr. Hagemeijer thinks that the virus's strength among wild birds may have weakened as the southward migration season progressed — a trait common in less dangerous avian influenza viruses, he said. That probably limited its spread to Africa, he said.

H5N1 is the most deadly of a large family of avian influenza viruses, most of which produce only minor illness in birds. Many avian influenza viruses are picked up by migratory birds in their nesting places in northern lakes during the summer and autumn 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," he said.

Still, this means that the cycle could well start again this summer, if the H5N1 virus — which can live for long periods in water — has persisted in those breeding areas. Many bird specialists believe that a small number of wetland lakes in Central Asia and Russia may harbor the H5N1 virus all the time, serving as the origin of European and Central Asian infections.

In fact, so much remains uncertain about the path of the virus that the European Union and some countries, like Germany, have decided to keep at least some precautions in place. Germany this week extended a law, due to expire May 15, that keeps poultry inside if they live near wetlands or in other areas that have had bird flu cases.

"There is still no systematic risk assessment — we've tested thousands of birds, but really tens of thousands need to be tested," Mr. Hagemeijer said.

Scientists still do not know which birds carry the virus silently and which die from it quickly, or also how it typically spreads from wild bird to wild bird, or between wild birds and poultry.

At the Beijing donor conference sponsored by the World Bank, $1.9 billion was pledged. "But none of it was for researching the role of wild birds," Mr. Hagemeijer said. "It was all for stockpiling Tamiflu" — the anti-viral drug for use against bird flu.

The disappearance of the virus from wild birds in Europe would be important, nonetheless, because it is easier to monitor a virus that exists only on farms.

Farm-based outbreaks of avian influenza are still occurring constantly in a number of countries, although not in Europe. The Ivory Coast had its first outbreak of bird flu, on a farm, last week.

But other countries, like Turkey, have made good progress in containing the disease among poultry, Dr. Lubroth said. He added that he hoped that quick measures to limit outbreaks had reduced its spread in Africa.

After the disease was found on farms in Nigeria in January, most experts expected it would 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?" Dr. Lubroth asked.

"All we have are a few snapshots of the virus. What we need is a movie of its life cycle."
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