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Avian influenza (Bird flu): GB surveys of wild bird populations to screen for the presence of Avian Influenza

Overview

Avian influenza is caused by an avian influenza A virus of which there are many different types. They can be characterised by their structure or the severity of disease that they cause in poultry.

There are 2 proteins on the surface of the avian influenza virus, Haemagglutinin (H) and Neuraminidase (N). The structure of these proteins can vary; so far a total of 16 different Hs and 9 different Ns have been identified. The virus can be classified according to these i.e. H5N1, H2N2, H7N3; in this system each different virus is known as a subtype.

Avian influenza viruses that cause severe disease in poultry are known as highly pathogenic influenza (HPAI) viruses, those that cause no disease or milder disease are called low pathogenic avian influenza (LPAI) viruses. The ability to cause severe disease depends on the molecular structure of another part of the virus called the cleavage site. Subtypes H5 and H7 may cause LPAI or HPAI, all other subtypes to date have only been known to cause LPAI.

Surveillance

Surveillance for avian influenza viruses in domestic poultry and wild birds is part of a European initiative and is carried out in all European Member States.

The UK strategy for avian influenza surveillance includes:

The UK wild bird survey for avian influenza viruses

There are a number of ways in which highly pathogenic avian influenza (HPAI) H5N1 viruses may be spread, including the movement of infected poultry and poultry products and the movement of contaminated vehicles, clothes, objects and utensils. It is thought that wild birds have the potential to play a role in the spread of HPAI H5N1 to domestic poultry. The wild bird survey provides an early warning if highly pathogenic avian influenza H5N1 viruses are introduced into the UK in wild birds and an assessment of the risk of introduction into domestic poultry.

There are an extremely large number of wild birds in the UK, only a proportion of these are migratory. Although over 10,000 birds will be tested in 2008, this is a small fraction of the total wild bird population (there are approximately 5 million water birds in the UK during winter months). It is not practical to sample a large percentage of these. This is why it is important to target surveillance to areas and species where the likelihood of detecting H5N1, if it were present, would be greater.

The survey focuses on species of wild birds that experts believe to have a greater potential role in the spread of avian influenza viruses. There is a comprehensive list which generally includes ducks, geese, swans, gulls and waders. Sampling is targeted as much as possible to areas where there is an abundance of these migratory water bird species and domestic poultry. The aim of this is to focus on areas where an introduction of HPAI H5N1 would be more likely to be detected if it had occurred and to areas where an introduction may have more significance to poultry health.

Surveillance focuses on periods when there are greater numbers of migratory water birds residing in the UK. Most migratory water birds tend to leave the UK for their summer breeding grounds, in more northerly latitudes, during the spring time. In the autumn when day length shortens and temperatures start to drop many migratory water birds travel south again to warmer areas such as the UK where they spend the winter months. Wild bird survey efforts are therefore focused on the autumn migratory period and over wintering period.

It is normal for a proportion of wild birds to carry low pathogenic avian influenza viruses so it would not be unusual to detect some LPAI viruses over the course of the survey. These are normally of little significance to human or animal health.

During 2007 HPAI H5N1 was detected in a number of wild birds in several European countries.

There are three components to the wild bird survey:

  • Sampling of live caught wild birds
  • Sampling of birds shot during normal wildfowling activities (no birds are shot in addition to those that would normally be shot by hunters)
  • Screening of wild birds found dead
1. Survey of live caught birds to identify the presence of avian influenza virus:

Samples are collected from the live caught birds, at several wetland sites throughout the UK. Birds are caught, ringed and sampled. The birds are released and samples are screened for avian influenza viruses.

2. Survey of shot birds to identify the presence of avian influenza virus:

This part of the survey is coordinated by the British Association for Shooting and Conservation (BASC). As part of normal wildfowling activities hunters are collecting samples from birds that have been shot; these are then screened for the presence of avian influenza viruses. No birds are shot in addition to those that would normally be shot during hunting.

This takes place during the wild fowling season, which extends from September to February each year.

3. Targeted screening of wild birds found dead in designated surveillance areas

Species that are considered by experts to be more likely to play a role in the spread of HPAI H5N1 will be considered for laboratory screening. The types of birds that will be considered are gulls, ducks, geese, swans and waders. Generally speaking these birds will have webbed feet, long legs or long necks.

This surveillance is targeted to areas where there is a greater abundance of poultry and water birds. A sample of dead wild birds found in these designated priority surveillance areas (see map below) will be considered for screening. The surveillance areas will be kept under review.

The survey is a strategic targeted survey and not all birds will be collected. The likelihood of a wild bird that is found dead being infected with avian influenza is very small. Dead wild birds are screened because they are a convenient source for sampling and not because their death is likely to be due to avian influenza.

Samples will be collected as a result of regular patrolling of certain wetland reserves and reports made by the general public within the surveillance areas.

Patrolling of reserves

Selected reserves across the UK will be patrolled on a regular basis by staff at the sites during autumn, winter and early spring. Dead wild birds belonging to certain species will be submitted for avian influenza virus screening. The frequency of patrols and number of patrolled sites may be increased in an area where there is a known increased risk of HPAI occurrence.

Public reporting

If dead wild gulls, waders, ducks, geese or swans are found and you are within a survey area or unsure whether you are in a surveillance area you may wish to contact the Defra Helpline 08459 33 55 77, 8.00am to 6.00pm Monday to Friday. An assessment will then be made and a decision as to whether the bird(s) will be collected for screening.

When reporting dead wild birds please have the following information ready before calling the helpline:

  • The administrative area that you are in (i.e. Essex, Bolton, St. Helens)
  • A description of the bird. Collection will only be considered if the bird is a duck, swan, goose, gull or wader. It must be in good bodily condition.
  • A detailed description of the area must be given to the helpline so that someone that is not familiar to that area will be able to find the bird(s) easily if there is to be a collection. If the bird(s) is not accessible it cannot be collected.
Wild bird surveillance priority counties map

There will be a response to a sample of calls, so not all dead birds will be collected.

In Great Britain if dead wild birds are collected for screening they will be taken to a local regional Veterinary Laboratories Agency (VLA) lab in England and Wales and Scottish Agricultural College (SAC) lab in Scotland. Further samples will then be taken and sent to VLA Weybridge for testing.

A Wild bird surveillance priority counties map is available.

Defra Helpline 08459 33 55 77, 8.00am to 6.00pm Monday to Friday.

In Northern Ireland - reports are directed to the DARD helpline (Tel. 028905 24999).

The investigation of unusually high mortality events in wild birds

This is separate survey to establish the causes of deaths of large numbers of birds (die offs). It has been running for several years now and was established before the avian influenza survey. Die offs may be the result of poisoning, adverse weather conditions, starvation or one of a number of infectious diseases. They are unlikely to be the result of avian influenza, although, amongst other things, samples are screened for avian influenza viruses.

As part of routine wildlife disease surveillance we will be undertaking post mortem examination of birds in incidents where 10 birds are found dead in the same location and at the same time. This is called a 'mass mortality event'. Inside the avian influenza surveillance areas these incidents should be reported to the Defra helpline. If the location is outside the surveillance areas, members of the public may report the situation directly to the regional VLA laboratory (or SAC in Scotland) who will decide if the deaths should be investigated further (the helpline can advise on the local regional laboratory and the contact number).

It should be made clear to the Defra helpline if the call relates to the wildlife disease survey for mass mortality events in birds, since this is a separate survey.

Further information on wildlife disease surveillance is available here.

Defra Helpline 08459 33 55 77, 8.00am to 6.00pm Monday to Friday.

In Northern Ireland, reports are directed to the DARD helpline (Tel. 028905 24999) where an initial assessment is made. If the die off is suspicious, the caller is referred to DARD’s Veterinary Service where a further assessment is made.

Further information

Page last modified: 23 January, 2008

Department for Environment, Food and Rural Affairs