July 5 (Bloomberg) -- France found three wild swans that died this week had avian flu, suggesting the lethal H5N1 virus is spreading again across Europe.

At least five other European nations have reported avian influenza outbreaks this year, according to the Paris-based World Organization for Animal Health. A strain that killed 12 wild birds in Germany in the past month is almost identical to that found earlier this year in the Czech Republic, Germany's Friedrich Loeffler center for animal health said.

This year's outbreaks probably spread through the migration of infected water birds. They leave traces of the virus on the surface water when they touch down on lakes, in turn infecting less transient local birds. Dead swans are often the first sign of an outbreak, said Albert Osterhaus, director of New-Flu Bird, a European project based in the Netherlands bringing together ornithologists and virologists.

``They are the sentinels of the disease'' and may indicate that more avian infections will follow, Osterhaus said in a telephone interview.

World health officials are tracking the spread of H5N1 in birds in the event that the virus adapts to become more easily transmitted among people, sparking a pandemic. Since 2003, the virus has sickened 317 people in a dozen countries, killing 191 of them, according to the World Health Organization in Geneva.

The H5N1 virus reached the European Union for the first time last year, starting in Greece and Italy and reaching birds in France, Germany and a dozen other nations on the continent.

Testing Birds

France's agriculture ministry today confirmed that three swans found dead on a lake in the Moselle region, which borders Germany, died of bird flu.

Germany's Friedrich Loeffler center is testing the carcass of another bird found in the province of Thuringia as well as soil samples that could tie the deaths to the strain of H5N1 virus found in other countries.

Authorities have sealed off a 3-kilometer (2-mile) area around the find. A further 10 kilometers function as an observation perimeter. Thuringian authorities have ordered all poultry within the area to be kept in their pens as a precaution.

The virus has now emerged in four German states. More than 100 dead birds were found at the Kelbra lake on the border of Saxony-Anhalt and Thuringia, 39 of which died of the virus, the Friedrich Loeffler center said in a statement today. Thirteen of the cases were of the highly infectious ``Asia'' type, the center said. The center said there is a high risk of the virus spreading to local poultry.

Poultry in France's Moselle region also has been confined and local wildlife is under observation. The Netherlands, which hasn't reported any H5N1 infections, today ordered a ban on keeping domestic fowl outdoors. The ban doesn't apply to poultry kept as a hobby or birds vaccinated in the past year.

``The measures show an increase in awareness,'' says Alex Thiermann, president of the Code Commission, a Paris-based standards setting body for animal health.

Possible Austrian Outbreak

The effect on poultry farming will probably be limited, Thiermann said. Confinement will not stop bird flu spreading among wild birds, though it does make it tough for the virus to leap from wild to domestic birds, and any cases of infected poultry will be limited to individual farms, Thiermann said. The danger to the human and commercial bird population will be limited if vigilant measures continue to be enforced.

Eight dead birds have been found since July 3 on a promenade in the Austrian town of Altmuenster, which is situated on a lake, ORF state television reported on its Web site. The state veterinarian began testing them immediately for bird flu, and the results won't be known for two or three days, ORF said.

Migratory patterns are hard to predict this year. Birds typically fly from cold spots to hotter ones. This summer, heatwaves in parts of Europe make it more difficult to determine avian routes.

``Birds aren't like British Airways; they don't always fly between Moscow and London,'' said John Oxford, professor of virology at St Bartholomew's hospital in London. ``They know roughly where they are going, but they don't always end up there.''

To contact the reporters on this story: Nicholas Comfort in Frankfurt at ncomfort@bloomberg.net; Angela Cullen in Frankfurt at acullen8@bloomberg.net

Last Updated: July 5, 2007 12:01 EDT