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http://www.nytimes.com/2006/03/06/international/europe/06flu.html

Recent Spread of Bird Flu Confounds Experts

By ELISABETH ROSENTHAL

Published: March 6, 2006

OZZANO EMILIA, Italy As new outbreaks of bird flu have peppered Europe and Africa in recent weeks, experts are realizing that they still have much to learn about how migrating birds spread the A(H5N1) virus, leaving the continents vulnerable to unexpected outbreaks.

After new scientific research published in February clarified the role of wild birds in spreading the disease from its original territory in southern China, the virus promptly moved into dozens of locations in Europe and Africa, following no apparent pattern and upsetting many scientific assumptions about the virus and its course around the world. In fact, knowledge of how the virus is spreading in Europe and Africa is so rudimentary that experts say there is no way of predicting where it will strike next, although they are now certain that it will, again and again.

"We know next to nothing about this virus; we have only anecdotal information about where it exists and what birds it infects," said Vittorio Guberti, head veterinarian at the Italian National Institute for Wildlife here in a rural corner of northeastern Italy. He has been studying influenza in wild birds for more than 10 years.

"We don't even know where to focus. We have to sit and wait for the big epidemic to occur, and in the meantime there will probably be small outbreaks all the time."

Scientists do not know, for example, which species are the major carriers of A(H5N1). While they suspect that there may be a few areas at the fringes of Europe that are perpetually infected with the virus, they are not sure exactly where. And while they are convinced that the virus can be carried on trucks, on soles of shoes and in fertilizer, they are not sure how significant those routes are.

"Think about this," Mr. Guberti said in his cluttered laboratory here. "Two million ducks from Nigeria, where there is a big problem, will arrive in Italy. And we don't know a thing about them."

Outbreaks in Nigeria have occurred in commercial poultry, but there is no information about whether the disease is in wild birds. Samples from African birds have been shipped to Italy for analysis, but the laboratory has been overwhelmed by samples from Europe, a United Nations official confirmed.

If they are infected, North American birds may be vulnerable, too, since some wading birds from Africa will fly as far north as Canada and the United States in the months to come, experts said.

While A(H5N1) does not now readily infect humans or spread from person to person, scientists are worried that it could acquire that ability, setting off a worldwide human pandemic. Until this year, Europe's small fraternity of wild bird researchers was severely underfinanced, its warnings about bird flu unheeded. Now the researchers are racing to fill gaps in knowledge and answer crucial questions.

In February, new research provided clues about how the A(H5N1) virus broke out of its original stalking grounds in Southeast Asia, moving to western China and on to the edges of Europe late last year.

Dr. Guan Yi and his colleagues at the University of Hong Kong reported in the Proceedings of the National Academy of Sciences that some birds infected with A(H5N1) could survive for a week, and so were capable of spreading the disease over vast areas to China's remote west and to Mongolia, for example. Previously, scientists thought that infected birds would be too sick to cover such distances.

From there, A(H5N1) predictably moved on to Russia, Ukraine, Turkey, Romania and the Balkans. But the recent pattern of spread, into European and African nations, has been far more confusing.

"For a couple of weeks, it was raining dead swans all over Europe, which left everyone scratching their heads," said Jan Slingenberg, a senior veterinary official at the United Nations Food and Agriculture Organization in Rome.

Wetlands International, a Dutch nonprofit organization that has sent teams to several African nations to sample wild birds, has made a list of 17 species it believes are particularly likely to spread A(H5N1) in Europe. There is no list for Africa or Asia. Some species, like pigeons, which have provoked angst in European cities, are not particularly susceptible, so there is little point in directing vigilance there, officials said.

Mr. Guberti and others say they suspect that there are now permanent reservoirs of the disease on Europe's doorstep, so that birds like the mute swan may pick up the disease every time they enter the Continent. Suspects include the Black Sea and the lower Volga River, areas that have suffered previous outbreaks of A(H5N1), and where mute swans often winter.

Nations must identify such reservoirs, Mr. Guberti said, so that scientists can see which birds live there and where they migrate, creating a kind of early warning system.

The dead ducks that have been found in various corners of Europe, from Geneva to central Italy and the suburbs of Lyon, have proved even more disquieting to scientists.

"It's hard to explain," said Alex Kaat, spokesman for Wetlands International, noting that scientists have no idea whether the ducks got the virus from infected poultry nearby, from mute swans, from another species that is spreading the disease undetected in Europe or if they are birds making an early migration from infected parts of Africa.

While ornithologists think that most of the cases in Europe are tied to migration, they are also quick to note that wild birds are sometimes unfairly blamed, as in Turkey and Nigeria. "It's easy to blame migrating birds, because then no one is responsible," said Juan Lubroth, a senior veterinary health officer at the Food and Agriculture Organization.

In Croatia, for example, Mr. Kaat said, fertilizer made of manure from infected poultry probably spread A(H5N1). The manure is commonly used to fertilize fish ponds, which are frequent stopover points for migrating birds that probably contracted the virus there, he said. The virus persists in water for weeks.

In Nigeria, the first huge outbreak occurred in January in hens in the north, a dry area far from the wetlands that are home to the country's migratory birds.

"The outbreaks were in the wrong place and at the wrong time of year," Mr. Kaat said.

Instead, he and others believe, Nigeria's problem was probably caused by the transport of sick birds or bird products infected with A(H5N1) from another country in Africa or even Asia.