07/04/2006
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Bird Flu in Britain - are wild birds to blame?

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Background

The confirmation that a dead Whooper Swan found recently at Cellardyke, Anstruther, Fife, was carrying highly pathogenic H5N1 Avian Influenza has brought the issue of bird flu back onto the news agenda. This is the first time the strain has been found in a wild bird in the UK, although H5N1 had previously been detected in birds held in quarantine in the UK after infected Taiwanese birds arrived at a centre in Essex last autumn.

In addition to the Cellardyke Whooper Swan, 14 more dead birds are presently being tested for the virus, 12 of which are believed to be swans, plus two other species. The species of swan have not been named, but if they are confirmed to be carrying the virus and are migratory Whooper Swans, then that would presumably have implications for containing the outbreak. As a result of increased public awareness, even more birds will presumably be reported to the authorities in the coming weeks. Testing of wild birds has been ongoing throughout the winter, but if anyone finds a dead bird and is unsure what to do then they should contact the Defra helpline on 08459 33 55 77.

During the past year, the virus has spread from southeast Asia, which had previously been the main focus of H5N1 outbreaks, to central Asia, before reaching countries bordering the Black Sea. The route of transmission has always been the subject of intense speculation. Poultry and cage-bird movements, and use of by-products from the poultry industry in farming, would appear to have contributed but the role of wild birds in carrying the virus to new areas has always been unclear. It is being suggested that the recent cold weather has increased the numbers of wild birds migrating through Europe and this has led to the rash of confirmed cases in wild birds in countries such as Germany, Denmark, Sweden, Switzerland and France, as well as here in Britain. The migratory bird theory seems to be used by Governments to explain the spread of Avian Influenza neatly, but looking at the Asian situation it would appear that the timings of outbreaks did not coincide with bird movements. Additionally, there are no known flyways for ducks, swans and geese to, or from, southeast Asia into Europe, so, despite media claims to the contrary, the migratory bird theory would appear to be a poor explanation for the spread of the virus into Europe. However, once the virus did reach Europe, through whatever means, the possibility that wild birds then assisted its spread within Europe is a more plausible one. Many thousands of wild, and healthy, birds have been tested for the virus, yet there have been no reported cases of Avian Influenza amongst those that have been tested. However, dead birds have been found, and tested positive, often in close proximity to poultry farms. Presumably it is unlikely that a sick bird would be capable of making long-distance movements whilst carrying the disease? Perhaps the wild birds are the victims, rather than the culprits!

The Cellardyke bird was initially believed to be a Mute Swan, and despite various bits of misinformation in the media, this species is not as migratory as other wildfowl such as Whooper Swans or grey geese. However, Mute Swans from northern and eastern populations do move south and west in search of less harsh conditions during cold weather, so it's not impossible that the victim was a migrant from Europe. A key question for assessing whether the Cellardyke bird has carried the virus from abroad, or picked up the virus from another source, will be finding out how long it had been in the area. Swans are very conspicuous, especially coastal birds, so discussion with local residents, including birdwatchers, could establish whether this was a newly arrived individual or whether it had been in the vicinity for some period of time. If the latter, then this bird would be most unlikely to have carried the virus from Europe and must have been infected from some other, local, source.

In Europe, one route for the spread of the virus is thought to be through contact with infected poultry or their faeces. Swans like to graze in open fields and, if these have been fertilized with poultry manure (a widespread practice, at least in eastern Europe), this could be how the swans get infected. So, whilst the media has been quick to point the finger at migrating birds, it seems more likely that the virus is being transmitted by inappropriate farming and agricultural practices in certain areas, together with the transport of poultry, and the illegal movement of cage-birds. Both take place 24/7, every day of the year, bear no relation to the seasons and, at a whim, can transport the virus to new areas away from the established routes of migratory birds. How can migratory birds carry the virus from southeast Asia to Europe when none of the species involved migrate on such a route?

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What is the risk in the coming weeks

It should be stressed that H5N1 is a disease of birds. The risk to human health remains extremely low. The virus, in its current form, is difficult for humans to contract from birds. Although human deaths have occurred in other countries, the numbers of cases have been very low and confined to people in very close contact to infected poultry. The number of people in this country living and working in such close proximity to poultry is so low that the chance of the disease spreading to humans is very small indeed.

Obviously, large numbers of migrating birds will pass through the Fife region of Scotland in the coming weeks. Results from tests on additional birds recently found dead are due soon, and they will alert the authorities to whether the Cellardyke bird was a one-off, or is part of a much more widespread problem. It is likely that the movement of large numbers of birds through this region poses negligible risk to the residents, or tourists, in that area.

How can birdwatchers help?

Birdwatchers can be of great assistance in staying alert for unusual cases of mortality or sickness in wild birds. Government advice states that you should contact the Defra helpline on 08459 33 55 77 or the DARD helpline (Northern Ireland) on 02890 52 56 18 if you find any of the following:

  • A dead swan, goose or duck, or
  • More than three dead birds of any one species in the same place, or
  • More than five dead birds of mixed species in the same place.

In such circumstances, do not handle any of these dead bodies yourself.