Government officials immediately implemented strict precautionary measures outlined by the European Union after the H5N1 virus was confirmed in wild migrating swans in Greece, Italy and Bulgaria.
Italian health officials held a crisis meeting after the discovery of the virus in 21 dead swans in three southern regions of Puglia, Calabria and Sicily.
But tests on a dead swan found in the Abruzzo region of central
Italy proved negative.
Greek farmers sought to reassure the public stressing that the bird flu cases near the northern city of Salonika concerned three wild swans and not farm poultry.
Greek authorities fear more birds may be infected due to the high number of migratory birds fleeing an exceptionally severe European winter.
More than 200,000 waterbirds spend the winter in Greece but hundreds of thousands fly over the country during the spring and autumn migration.
Bulgaria, which is bidding to join the European Union next year, said it was also taking all precautionary measures after confirmation a wild swan in the country's northwest had H5N1.
Virus found in Slovenia
The European Commission also announced that a dead swan in Slovenia, in the northeastern city of Maribor, was found to have an H5-type bird flu virus and further tests would determine if it was the deadly H5N1 strain.
Slovenia also adopted the EU measures to prevent the spread of the killer disease, which included establishing a three-kilometre protection zone around the area where the infected birds were discovered and a 10-kilometre surveillance zone.
Slovenia was also collaborating with authorities in neighbouring Austria.
The H5N1 strain has killed some 90 people so far, mostly in Asia.
The World Health Organisation (WHO) confirmed that four people in Turkey and one in Kurdish Iraq died from the H5N1 bird flu strain, the only deaths outside Southeast Asia and China.
Romania, which has been battling H5N1 for months, said preliminary tests detected the H5 virus at a 29th site in Tropaisar, near the eastern city of Constanta, but it had not yet been confirmed as H5N1.
Romanian officials also said two boys aged four and seven, who had been suffering from normal human flu when they visited a farm where the H5 flu was reported, had been sent to an infectious diseases hospital nearby.
Some authorities and ornithologists fear more birds may be infected with the lethal avian flu as swans fleeing the severe European winter have migrated to southern Europe.
The crisis will be reviewed by the EU's food and animal health committee at a meeting on Thursday and Friday.
Meanwhile in Asia, results of tests by the World Health Organisation (WHO) showed that two Indonesian women in their 20s who died in hospital last week were the victims of bird flu, taking Indonesia's human toll from the virus to 18.
Nigerian children tested
Nigerian doctors have tested blood samples from two children suspected of being Africa's first human victims of the deadly H5N1 strain of bird flu.
The children fell ill last week on a poultry farm in the northern city of Kaduna, a short distance from a second farm quarantined after 45,000 poultry died from the disease.
Nigeria announced tougher controls to prevent the spread of the epidemic, including a poultry cull.
Although Nigerian officials have formally confirmed the presence of H5N1 on only four farms in the north of the country, large numbers of birds have been dying in many others, sparking fears of an uncontrolled epidemic in Africa.