Health officials across Europe issued restrictions for commercial poultry farms on Wednesday after reports that the deadly bird flu virus had turned up at a surprisingly early date in migratory birds in several West European countries.
The virus was confirmed in mute swans in Greece, Bulgaria and Italy on Saturday, and in Germany on Wednesday. Likely cases were detected in the same species in Slovenia and Croatia on Sunday, Austria on Monday and Denmark on Tuesday.
Health officials had expected wild birds to carry the disease into Europe from Africa in the spring migration. But the swans were probably migrating south to wintering grounds on the Black Sea, officials said, and were driven west by unusually cold weather in Russia and Ukraine.
Although 91 people have died after picking up the virus from close contact with birds, the most immediate threat for Europe is an uncontrolled outbreak of the virus among domesticated fowl, which can rapidly decimate a national poultry industry. This strain of flu virus, H5N1, is highly contagious and lethal to birds, often killing tens of thousands of poultry at a time.
To avoid contamination of domestic animals, many European countries ordered poultry farmers to keep their flocks indoors.
Several new cases were reported Wednesday in the Baltic area, with German officials saying two swans found earlier in the week by vacationers on the resort island of Ruegen were infected with the H5N1 strain of flu virus. Previously, bird flu was reported in several Central European countries, including Romania and Bulgaria.
The German discovery was accompanied by new reports of dead birds elsewhere in Europe, most of them involving wild swans that are beginning to show up on their seasonal migrations from Africa to places farther north. As such, experts said, the wild birds pose a new danger of a far wider spread of the disease in Europe.