October 24, 2005

 

Spring migration poses risk of bird flu spreading further
 

 

Millions of migrating wild birds returning from the Black Sea and eastern Mediterranean next spring may pose the greatest potential risk of bird flu spreading widely through Europe, say officials and experts.

 

Scientists suspect migrating birds have carried the deadly H5N1 bird flu strain from Southeast Asia, where it arose among domestic poultry and spread to wildfowl. It recently arrived in the Balkans, the crossroads for migratory routes that loop across Europe.

 

"The spring migration of 2006 may result in the spread of the H5N1 virus further across Europe, since birds migrating from southern zones will have intermingled with European Russian and Siberian-origin birds in the 2005/2006 winter nesting areas," the Food and Agriculture Organization of the United Nations said in a recent report.

 

Birds in Turkey, Russia and Romania have tested positive for H5N1, which has devastated poultry industries in Southeast Asia and killed more than 60 people.

 

Cases of H5N1 were also confirmed south of Moscow Wednesday, indicating that the disease continues to spread westward.

 

The news put western Europe on alert.

 

"From what we know about the migration routes of birds, there is now a risk that birds from the affected area will come into Sweden," said Lief Denneberg, the chief veterinarian at Swedish government's Board of Agriculture.

 

Johan Stedt, ornithologist and location chief at the bird station on the Swedish island Oeland in the Baltic Sea, said wild ducks have been migrating from Russia to Sweden for about a month and will keep doing so until December.

 

While wildfowl winging through from Russia before winter pose an early risk, experts are more worried about what will happen in spring. It is then that birds return to Western Europe from Africa and the Eastern Mediterranean as part of a vast migration of ducks, geese, swans and other waterfowl.

 

Migratory routes used by birds largely overlap in Siberia and Ukraine on a southwest axis through the Balkans and eastern Africa, which include areas where western European birds are most likely to mix with birds from infected areas further east.

 

"It's a very large-scale phenomenon involving tens of millions of birds leaving Siberia and Northern Europe for the Mediterranean, the Black Sea and Africa," said Simon Delany of Wetlands International, a Netherlands-based conservation group.

 

Though still theoretical, an airborne migration of the H5N1 strain to western and northern Europe would be a continuation of how the virus is believed to have spread from Asia.

 

"It looks from the pattern that this is what is happening," said Delany.

 

Looking further ahead, he said shore birds and geese migrating across the Atlantic could in theory carry the virus to North America.

 

Scientists have not conclusively resolved the question of whether an infected bird can make a migratory journey.

 

The WHO said in a recent report that pathogenic or disease-causing viruses have been isolated from migratory birds on rare occasions involving a few birds, usually found dead within the flight range of a poultry outbreak.

 

"Recent events make it likely that some migratory birds are now directly spreading the H5N1 virus in its highly pathogenic form. Further spread to new areas is expected," the WHO said.

 

Concern is rising among European health officials as far north as Norway and Finland that infected waterfowl will spread the disease when they return in the spring.

 

Annual testing by Norwegian officials finds regular strains of bird flu every year, but so far not the virulent H5N1 strain that has world health officials worried about an epidemic.

 

"Fortunately, it is late fall, and the wild birds are migrating from north to south," said Gudbrand Bakken, director general of food safety at Norway's Ministry of Food and Agriculture. "The situation could change in spring, when birds start flying in from the Mediterranean and the South."

 

German veterinary groups are issuing similar warnings and the Netherlands has banned free-range poultry to minimize exposure. Switzerland, the UK and other European countries have begun routinely testing migratory birds.

 

UK authorities have set up a special hotline in the event of the discovery of a sudden "die-off" of unusual number of wild birds.

 

"So far our birds are coming from non-infected areas, so the risk of infection is small," said Martin Fowlie of British Trust for Ornithology. "But we're working with the government in regular testing."

 

The H5N1 virus in its current form can pass between wild birds and domestic poultry, but cannot be transmitted between humans. The risk is limited to people with close contact with infected ducks and poultry, according to the European Centre for Disease Prevention and Control. But scientists fear the H5N1 strain could mutate and become capable of passing between humans.

 

Although it rated the risk of bird flu spreading to humans in Europe as "close to zero," the ECDC Wednesday urged travellers to take precautions in areas where the H5N1 strain has been detected in ducks and poultry.

 

Europe is no stranger to other forms of bird flu. Holland suffered a crippling outbreak of the H5N7 strain in 2003, resulting in the culling of 30 million birds at a cost to the economy of hundreds of millions of euros.

 

"It's believed that the virus had been in waterfowl, but became more deadly when it spread to poultry and mutated," said Marion Koopmans of the Dutch National Institute for Public Health. "Where the infected waterfowl came from is anybody's guess."