Germany and Austria are the latest EU countries to report the discovery of dead swans infected with the H5N1 strain of avian influenza, that has spread from Asia to Africa and killed 91 people and led to the destruction of millions of birds.
The World Animal Health Organisation (OIE) says the cases themselves do not necessarily mean the disease has spread to domestic flocks. But, this is where governments should now concentrate their efforts as H5N1 is highly contagious among poultry.
A spokeswoman for the OIE said: "Little can be done about the migratory patterns of wild birds, therefore we emphasise the importance of minimising the opportunity for domestic birds to come into contact with wild birds."
Horst Seehofer, the German health minister, said authorities would now focus on preventing any transmission to livestock.
He brought forward a ban on keeping poultry out of doors to 17 February from 1 March.
In Austria, the Health Ministry said it had created a restricted zone within a 3km radius of where the dead swans were found, in the Styria region bordering Slovenia.
All poultry trade has been banned in the area for at least 30 days.
In the entire area, farmers will have to confine their poultry stock to barns.
Poultry markets and shows, and hunting for wild fowl, have been banned, the ministry said.
Farmers told to keep chickens
and turkeys indoors
The latest European cases follow the discovery at the weekend of the virus in Italy and Greece, putting governments as far north as Stockholm and Oslo on alert.
Sweden has ordered farmers to keep chickens and turkeys indoors, reinstating restrictions that were issued in the autumn and Norway has imposed a similar ban and stepped up its checks.
The Slovenian Veterinary Administration has ordered the confinement of all poultry in the country and authorities have told people to stay away from wild birds.
And the Swiss government on Wednesday ordered a nationwide poultry lock-up from 20 February.
In Italy, police impounded more than 80,000 chickens and 7000 eggs from farms in the south of the country as part of a major crackdown on health norms.
The new cases have had a dramatic effect on Europe's 20-billion-euro ($23.82 billion) poultry sector.
Chicken sales plunge
Sales in Italy have plunged more than 50% since the weekend, the farm union Coldiretti said, while others have estimated losses to the sector of one billion euros.
Nigerian authorities have killed
more than 140,000 fowl
In France, sales are down by 15% after recovering around Christmas, although they have held up in the UK, where 90% of poultry reared for meat is kept inside anyway.
Meanwhile, in Nigeria, authorities working to contain the deadly H5N1 virus in have killed more than 140,000 fowl, officials said Wednesday.
Shehu Bawa, head of Kano state's bird flu committee, said more than 30 commercial farms in the state alone have reported large-scale poultry deaths and health workers have killed more than 140,000 since Africa's first case was announced one week ago.
Three of Nigeria's 36 states have confirmed presence of the H5N1 bird flu strain, five others are testing suspected cases and the country to Nigeria's north, Niger, is investigating bird deaths that UN experts say are likely from H5N1.