According to European officials, the deadly H5N1 bird flu virus has been found in wild birds in Italy and Greece, and in Bulgaria.
This is the first time bird flu has been detected in the European Union nations.
The only previous proven case of bird flu on EU territory was in Britain, in a parrot imported from South America.
Francesco Storace, the Italian health minister, has said that five wild swans found in the southern island of Sicily and on the southern mainland had tested positive for the highly pathogenic version of the H5N1 strain.
In total 17 swans have been found dead in three southern regions, Calabria, Sicily, and Puglia.
Storace says that although no bird flu has been found in farm or domestic birds the transport of animals susceptible to the virus would be banned in the three regions.
As yet there are no signs of infection in commercial poultry.
Health officials in Sicily believe the swans migrated from Russia.
Dr. Juan Lubroth, a senior veterinarian at the United Nations Food and Agriculture Organization (FAO) in Rome, says bird flu has been expected to hit Western Europe for months.
The virus has been steadily spread by migrating birds from China, to Russia, and to the Balkans.
According to a spokesman for the Rome-based Food and Agriculture Organisation, it is confident Italy is able to deal with the outbreak and appears to have provided a model for early detection, demonstrating how bird flu can be controlled in countries that have the money and the scientific resources to do it.
It is clear that effective veterinary services and an advanced poultry industry which is not of the 'backyard' variety are important factors.
Health officials in Greece say that three swans found around the Thermaikos Gulf and sent to a British laboratory have also tested positive for the deadly strain, while results of tests on a wild goose on Skyros island in the Aegean are pending.
In Romania more infections are suspected in birds in the Danube delta and in Bulgaria European Union officials have also confirmed the presence of the lethal strain among swans in wetlands close to the Romanian border, a region considered to be a haven and transit point for migrating birds.
Preventive measures include isolating poultry and keeping flocks indoors, banning hunting, disinfecting farms and a ban on meat or eggs from the areas.
Bulgarian police are apparently planning to shoot wild dogs and foxes which might spread around the remains of infected birds.
According to Dr.Lubroth, dead swans have become an important flu sentinel because they are very susceptible to the virus and are so large that people notice when they die.
Late last year a number of European nations, including Switzerland, Austria and the Netherlands, mandated that all commercial poultry be kept indoors, to prevent any contact with migrating birds.
Greece now also requires that poultry be kept indoors and has banned the sale of live birds at street markets.
In an attempt to calm public alarm, the E.U. health commissioner, Markos Kyprianou, says the cases found in the European Union are not surprising and is not alarming when the framework is in place to contain and prevent the spread of the virus to poultry.
Dr. Julie L. Gerberding, director of the federal Centers for Disease Control and Prevention, is also not surprised that infected birds had been found in southern Europe as it has followed the flight patterns of migrating birds.
It seems the strain of the virus found in Turkey and confirmed in Africa last week is identical to one found last year in dead migratory birds in a nature reserve in northern China, and later in Siberia and is different from strains circulating among poultry in Southeast Asia and Indonesia.
Recent outbreaks in poor countries like Nigeria, Turkey and Iraq have simmered for months before they were discovered, which has encouraged the virus to spread widely to commercial chicken flocks and even to humans.
Nigeria has apparently started testing people who have fallen ill close to where the virus has been found among birds and farmers have culled thousands of chickens.
Angola, Mali and Guinea have joined other African nations in banning poultry and egg imports from Nigeria.
At present the virus does not readily spread from human to human, and is caught by close contact with sick birds.
To date, since 2003, only 160 people have become infected with the disease and about half of them have died.
It has forced affected nations to cull millions of domestic fowl.
Experts fear that the virus could mutate into a form where it can spread from human to human, exploding into a global pandemic in which millions could die.
David Nabarro, who heads the U.N. drive to contain the virus, said this week there was no evidence it had done so, but believes it is imminent.
Finance ministers of the Group of Eight (G8), meeting in Moscow, discussed the risk of a worldwide pandemic and issued a new call for wealthy countries to help poor ones fight bird flu.
The World Health Organisation (WHO) says 70,000 treatment courses of Tamiflu have been delivered to Iraq and will be taken to the north which has seen outbreaks among humans.
Meanwhile Indonesia officials say a 27-year-old woman has died of the disease; the death is the second in two days.