Abstract from BTO Research Report No. 448:

Humphrey Q P Crick, Philip W Atkinson, Stuart E Newson, Robert A Robinson, Lucy Snow, Dawn E Balmer, Dan E Chamberlain, Jacquie A Clark, Nigel A Clark, Peter A Cranswick, Ruth L Cromie, Baz Hughes, Mark J Grantham, Rebecca Lee & Andrew J Musgrove

Avian Influenza Incursion Analysis (through wild birds)
ISBN No 1-904870-87-2

Executive Summary

1) Avian influenza (AI) is a contagious disease of animals caused by influenza A viruses. A small number of AI virus strains can cause a high number of deaths in domestic poultry flocks, these are known as Highly Pathogenic AI (HPAI). A particular strain of HPAI has been causing worldwide concern recently: the H5N1 strain has resulted in the death of more than 150 million poultry worldwide, through infection or attempts to control its spread.

2) Since 2005, when outbreaks of HPAI have been found in Europe (including Britain in the spring of 2006), Defra has sought the advice of an ornithological expert group to assist in making Qualitative Risk Assessments (QRAs) of the likelihood of the disease spreading to and within Great Britain though wild bird movements. Defra commissioned this project to develop methods of analysing rapidly the large datasets on bird movements and abundance held within Britain. The aim was to create ‘tools’ that would allow rapid risk assessments in the case of future outbreaks in or near populations of wildbirds that might migrate to Britain.

3) British Bird Biology Spreadsheets were developed to contain information on all bird species occurring in the wild in Britain. This includes information on migratory status, as well as the summer and winter ranges of each species and the months during which the species occurs in Britain. The spreadsheets provide a ready source of information for reference should a species be reported as carrying HPAI in Europe or elsewhere. In addition, there are worksheets of information on the worldwide occurrence of AI in bird species found in Britain and of the results of surveillance for HPAI in bird species found in Britain.

4) A Migration Mapping Tool was developed to provide a rapid assessment of information on the movements of marked birds for migrant species found in Britain. The methods developed as part of this tool, allow a rapid assessment of (a) main directions of movement made by a species to and from Britain; (b) timing of migration along the routes identified; and (c) the geographical spread of the population that visits Britain at different times of the year. By combining sophisticated statistical smoothing techniques with the capabilities of geographic information systems (GIS) we have been able to present a much more accurate pattern of bird movements than has hitherto been possible. As examples, the seasonal pattern of movements of 12 species that are thought to pose a particularly high HPAI incursion risk are presented in a readily interpretable way. Such maps can then be used to assess the likelihood that a species, found with HPAI in Europe or elsewhere, could migrate to Britain.

5) A Priority Surveillance Mapping Tool was developed to allow an assessment of the priority areas for surveillance with respect to the relative abundance of wild bird populations and of poultry. Data from a wide range of major national bird surveys were used to allow the creation of single and multi-species abundance maps for each month, at the 10-km square spatial scale. This was combined with spatial data from Defra’s Poultry Register to allow an assessment of areas where surveillance could be targeted should HPAI reach Britain. Information on domestic poultry holdings was used to rank them according to the estimated likelihood of an incursion of H5N1 directly from a wild bird source. The combined maps show areas where high abundance of wild birds and potentially susceptible poultry co-occur, though these are still subject to further refinement.

6) Poultry Incursion Likelihood Mapping was developed that is based on the priority surveillance mapping tool but introduces weightings for a variety of factors, such that wild birds most likely to transmit H5N1 to domestic poultry would contribute more than others. The aim is to provide a tool that would consider a wider group of species that might transmit HPAI to poultry, should HPAI become established in wildbirds in Britain, and identify priority areas for surveillance. The method developed is readily adaptable and is likely to require further refinement as the needs for such a tool become defined.

7) A Cold Weather Movements Review was undertaken to provide an overview of evidence for the large but irregular movements of birds in response to periods of severe weather in winter. Geese, ducks and waders are all likely to move to Britain from continental Europe in substantial numbers. The web-based Bird Track scheme for the daily reporting of bird lists provides a potential medium for the rapid monitoring of cold weather movements and might aid HPA1 surveillance targeting under such conditions.

8) The tools developed as part of this project make use of a wide variety of data sources that have a range of potential caveats or biases that need to be considered carefully. It is anticipated that the results from such tools would be presented only after suitable interpretation by ornithological experts.

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