Wild bird experts say risk is low

Photo: Jill Pakenham/BTO

Leading bird organisations have said that the risk of migrating birds bringing the H5N1 avian influenza virus to the UK is low.

In a joint statement the RSPB, BirdLife International, World Wildlife Trust and the British Trust for Ornithology have said that despite the current outbreaks and recorded deaths—predominately in waterfowl—there is, as yet, no definitive proof that migratory birds have transmitted the disease between countries or regions within countries.

"However," say the organisations, "the possibility remains that migratory birds may have played a part in transmission of the virus and we cannot ignore this possibility.

"Although there is a theoretical risk that migrating birds could bring H5N1 to the UK, at present we consider that risk to be small."

There are numerous strains (at least 135) of Avian Influenza, many of which circulate in wild birds at low levels, but which can occur more frequently in water birds. Most of these do not affect wild birds or only cause mild illness. High pathogenic Avian Influenza viruses, while causing severe mortality in poultry, are very rare in wild birds. The current strain of concern, H5N1, was never recorded in wild birds before the recent outbreaks in SE Asia and Russia.

It is likely that this highly pathogenic strain originated in domestic poultry through recombination of low pathogenic sub-types and was subsequently passed from poultry to wild birds. Husbandry methods in SE Asia where domestic flocks are often allowed to mix freely with wild birds, especially waterfowl, will have facilitated the transmission to migratory water birds.

But the bird organisations—backed by other bodies such as the World Health Organisation and World Organisation for Animal Health—believe strongly that culling wild birds is not feasible and should not be attempted.

"It is not yet clear whether wild birds are spreading the disease," they say, "but even if they are, we believe that culls of wild birds are highly unlikely to stop the spread.

"Indeed, culls have the potential to make the situation worse by dispersing infected individuals and stressing healthy birds, making them more prone to disease. "Moreover, it would divert resources away from important disease control measures."

Species which come to these shores from Russia are listed below, although most birds breeding in affected areas will be migrating further south and east of the UK.

Bewick's swan White-fronted goose

Brent goose Mallard

Teal Pintail

Pochard Wigeon

Shoveler Tufted duck

Bar-tailed godwit Grey plover

Lapwing Dunlin

The risk of infected birds arriving in the UK will depend on what proportion of the breeding population has come into contact with the infection, the transmission rate of the virus and the likelihood that an infected individual could undertake a long-distance migration. Currently these factors are difficult to quantify say bird experts.

Surveillance of wild birds

Wild birds should be tested for bird flu along major migratory paths in Europe to try and stop the disease entering the EU, says the Commission following a meeting of veterinary experts earlier this month.

They concluded that a sample of migratory birds should be tested as a further defence mechanism against the spread of the highly pathogenic H5NI strain of avian flu from Asia to Europe.

The experts said it would be wise to identify a list of the species of bird that pose the highest risk based upon origin, migratory routes, number of birds in the EU and the likelihood of contact with domestic poultry.

Sites most at risk, for example, free-range sites and those smaller batches of birds kept close to domestic poultry farms, should also be identified.

The Commission agreed that surveillance should also be extended to dead wild birds where the reason for death appeared abnormal or several birds of the same species were found dead at the same site.

A list of birds likely to present a higher risk of catching and transmitting avian flu was drawn up, though the Commission stressed that this was purely provisional. It included oft sighted birds such as the mallard and common gull, along with rarer species like the garganay and gadwall.

Member states are to use these proposals in conjunction with previous advice given by the Commission to put together a surveillance programme for 2005/2006.

Defra's chief veterinary officer, Debbie Reynolds, says officials in the UK, with the help of ornithology experts, are "reviewing urgently" the current surveillance programme.

See also

Every fifth US duck has flu virus

Vaccination or mass slaughter?

Are you, your family and staff at risk?

Avian Influenza – a new millennium bug?