Avian influenza (Bird flu): Summary of avian influenza incursion analysis work lead by BTO and VLA
Wild birds are considered to be one of a number of factors implicated in the spread of HPAI H5N1; however there are still uncertainties about the role that they play. Wild bird surveillance aims to improve our understanding of this potential role and act as an early warning should the virus be detected in wild birds in certain areas, so that measures can be taken to reduce the likelihood of introduction to domestic poultry.
The analysis lead by VLA and BTO aims to assess the relative risk of HPAI H5N1 introduction to domestic poultry from migratory wild birds across GB. This will inform targeting of wild bird surveillance to areas where wild birds are more likely to introduce avian influenza, should it occur in Europe, and where the implications of such an event could be potentially significant to poultry health. The analysis does not take into account other risk factors such as the movement of poultry and poultry products, vehicles, equipment, associated staff etc.
Analysis of commercial poultry populations and migratory water bird abundance across GB:
To assess the risk of introduction of avian influenza into GB by wild birds and subsequent risk to domestic poultry, an analysis was made based on the abundance of specific water bird species and poultry in each 10km square of the GB national grid.
The analysis focussed on 24 wild bird species (based on a list of higher risk species compiled by European Food Safety Authority (EFSA) ), which according to expert opinion have an increased likelihood of playing a role in the spread of HPAI H5N1 than other species that migrate to GB. Using survey data from a number of schemes, abundance scores (0-5) were assigned to each 10 km square for each bird species in each month. The probability of HPAI H5N1 incursion is likely to be greatest in October to December, following the main arrival of migratory water birds in GB . The maximum score recorded for each 10 km square for each species over this three month period is taken to produce a map for each of the 24 species. The data from all 24 species was then combined in a single map.
Using information from the GB poultry register, domestic poultry holdings with chickens, ducks, geese or turkeys, were ranked according to the relative likelihood of HPAI H5N1 infection from a wild bird source, irrespective of wild bird populations in that area. The holdings were ranked (by scores) according to a number of holding-level factors. These included the number and species present on the holding and housing type (indoor or outdoor). Scores were added together across holdings to give a total score for each 10km square.
A single priority area map for surveillance was calculated by multiplying the wild bird abundance and poultry scores, above, for each 10 km square. Squares were ranked 1 (high) to 6 (low) based on their relative priority for surveillance.
Selection of high priority survey areas for public reporting of dead wild gulls, waders, swans, ducks and geese:
Scores were calculated for each county as the average score for all 10km squares with any land within the county boundary. The high priority surveillance counties were then identified as the top one third of all counties in GB with the highest average scores. The top scoring one third of counties in Scotland were also highlighted along with the Scottish Borders region. The Isle of Anglesey and Devon were selected because of the exceptionally high poultry and wild bird scores for these areas and for geographical coverage.
Selection of reserves for patrolling for dead wild birds belonging to the list of 24 higher risk wild bird species:
Bird/nature reserves targeted for patrolling were identified according to their proximity to high ranking surveillance 10 km squares and the resources available for patrolling such sites.
Page last modified:
14 November, 2007