German medical experts have warned that a strain of the bird flu virus is spreading rapidly across northern Europe, most likely being carried by wild birds that do not show any symptoms.
Thomas Mettenleiter, president of Germany's animal-health-monitoring Friedrich Loeffler Institute, issued the warning on November 23.
Mettenleiter said the H5N8 virus is now jumping from wild birds to domestic fowl on northern European farms.
He said the virus has been detected in 10 German states since it was first registered in the country on November 8.
Cases have also been reported in other European countries, including Denmark and Sweden -- which announced on November 23 that its first case of the disease was confirmed in a wild bird in the south of the country.
Further tests were being carried out on a poultry farm in southern Sweden.
H5N8, which is not thought to be dangerous to humans, was first found on the border of Russia and Mongolia in June.
Since then, it also has been found in Iran and Israel.