The spread of bird flu across Europe, thought to be caused by waterfowl from the Black Sea, risks increasing when birds soon start migrating north from Africa, experts said on Monday.

The H5N1 strain of the virus has now been found in France, Germany, Italy and Greece, mostly either in wild swans or, as in France, a species of wild duck. Europe’s one-billion-strong domestic poultry flock has not been infected so far.

The virus is also spreading fast in poultry in Nigeria.

Conservation groups, which stress the role of illegal poultry trading in the spread of bird flu, say the recent plunge in temperatures in bird flu infected Black Sea regions has pushed wild swans westwards in search of new feeding grounds.

“Mute swans are not migratory but under certain circumstances, if they face extreme conditions, they will move,” said Adrian Long, spokesman for Birdlife International.

He said it was likely the swans were infected before starting their journey from countries around the Black Sea with a record of bird flu and lax controls over infected poultry.

Experts believe migrating birds or illegal trade was responsible for carrying the virus to the Black Sea from Asia, where the H5N1 virus originated.

Poor poultry biosecurity in Black Sea outbreak zones, including the illegal dumping of infected meat and the use of poultry manure, can create hotspots for the virus, Long said. “If these biosecurity ‘hotspots’ are not properly managed, then we will see wild birds spread the disease,” he said.

This is why experts believe the spread of the virus within Nigeria is so dangerous for neighbouring countries and in terms of the spring migration northwards, for Europe.

NORTHERN MIGRATION

Poor controls and the many backyard farms have allowed the H5N1 strain to take hold in Nigeria’s poultry flock, meaning the virus could easily spread to neighbouring countries and beyond.

The French case of an infected Pochard duck may have come from eastern Europe but conservationists said there was a slim chance it was a first infection from West Africa, where small numbers of Pochards winter in the Sahel region.

“The remote possibility exists that an early migrating bird from this tiny West African wintering population of Pochards transported the disease from Nigerian outbreak areas to France,” said Ward Hagemeijer of Wetlands International.

Several species of migratory waterbirds are known to fly to West Africa from Europe and the Black Sea regions in the autumn and return in the opposite direction in the spring.

Wetlands International said the Garganey, Northern Pintail and the Northern Shoveler were species considered a higher risk of carrying H5N1 because of their migration patterns, habitat preferences and tendency to mix with other species.

There are some two million Garganey ducks wintering in west Africa, concentrated in the Sahel zone from Senegal to Chad.

“January 2006 was exceptionally cold in eastern Europe, including the Black Sea region, and this may have pushed more birds than usual into Africa,” Wetlands said.

Wetlands said the return migration will take place in March and April for most species, although some can start by late February. From northern Nigeria, most would migrate directly across the Sahara and then across the central Mediterranean.

Others take a more easterly route through the Middle East, and it is likely that some take a westerly route through Iberia.

“Three of the higher risk species identified by Wetlands International are known to migrate in numbers from breeding grounds in Europe to wintering grounds in Nigeria, and the return migration of all three can be expected to start before the end of February,” Wetlands said.