Landscape elements and land use in the immediate vicinity of poultry farms are important risk factors for the introduction of highly pathogenic bird flu on commercial poultry farms. This is apparent from an analysis by Wageningen Bioveterinary Research, part of Wageningen University & Research. The report has been submitted to the House of Representatives as an appendix to substantiate the letter to parliament ‘Intensifying the Approach to Bird Flu’.
Risk factors investigated
From 2014, commercial poultry farms will be infected with highly pathogenic bird flu virus (avian influenza (HPAI)) almost every bird flu season. Since that time, migratory birds bring HPAI viruses to the Netherlands in the autumn. These migratory birds come into contact with migratory birds from Southeast Asia infected with HPAI on common breeding grounds in Siberia. Wild waterfowl living locally in the Netherlands also become infected through direct contact with the migratory birds and through migratory bird-contaminated surface water. Together they pollute the yard and the area around the poultry sheds with their droppings. Commissioned and financed by the Ministry of Agriculture, Nature and Food Quality, Wageningen Bioveterinary Research (WBVR, part of WUR) investigated risk factors for the introduction of HPAI virus in commercial poultry farms in the Netherlands.
Analysis of suspected risk factors
The analysis of suspected risk factors was done in a similar way to previous research on the introduction of the low pathogenic variant of the bird flu virus (LPAI) in the period 2007-2013. That research showed that the introduction risk differs between business types. The analysis also showed that certain types of landscape elements increase the risk of introduction.
For the current study on the risk factors for infection with HPAI virus, data from 2014 to June 2022 was used. These came from 71 infected commercial poultry farms. In addition, all non-infected poultry farms in the Netherlands were included in the study. In addition, the density of wild bird populations (birds per km2) around commercial poultry farms was looked at, a factor that was not part of the research on the LPAI variant of the virus.
Factors that increase risk
The data analysis shows that a number of factors increase or decrease the HPAI introduction risk on poultry farms (see also table). “Duck and turkey farms have the highest introduction risk of the various poultry farm types, broiler farms have the lowest introduction risk,” says epidemiologist Armin Elbers of WBVR. These findings are similar to the results of the LPAI study.
Presence of water
“We also see that the introduction risk of HPAI increases as the surface water in the vicinity of the poultry farm increases and the distance from the poultry farm to the water decreases. The presence of water in the immediate vicinity of poultry farms is an attractive living environment for waterfowl,” says Elbers.
Presence of grassland
Another important aspect is the possibility for wild waterfowl to forage in the immediate vicinity of poultry farms. “The larger the area of grassland around the poultry houses, the greater the chance of an introduction of HPAI on a poultry farm.” The presence of forest in the immediate vicinity of a poultry farm reduces the risk of introduction. “This is probably because the proximity of forests is less attractive as a habitat for wild water birds, as opposed to open (grass) meadows.”
Geographical location
The geographical location of the poultry farm in the Netherlands is also important. “HPAI introduction risk increases from East to West and from South to North. This probably has to do with the frequent presence of wetlands in the west and north of the Netherlands.”
Bird species
The researchers also looked at the density of different groups of wild birds in the immediate vicinity of poultry farms. This study shows that of all groups of wild birds, the density of gobies – a group that includes the mallard, widgeon, pintail, teal and garganey, gadwall and shoveler – has the strongest relationship with HPAI introduction risk on commercial poultry farms. . “The densities of gobies and geese, swans and diving ducks around poultry farms are closely related, so the presence of these other bird species is also important. But the relationship of these other bird species with the HPAI introduction risk is less strong than that of the gobies,” explains Elbers.
“The three factors of poultry farm types, environmental landscape elements and geographical location best explain the HPAI introduction risk on poultry farms,” concludes Elbers based on the study. “Duck density around poultry farms is a much weaker variable.”
The full report is available on the Wageningen Bioveterinary Research website.
Table. Key explanatory factors for the introduction of HPAI on commercial poultry farms:
- Business type:
- Duck and turkey farms have the highest HPAI introduction risk;
- Breeding, breeding and laying farms have a mutually comparable HPAI introduction risk;
- Broiler farms had the lowest HPAI introduction risk;
- Landscape elements:
- Water surface in the immediate vicinity of the poultry farm;
- Distance from the nearest available water to the poultry farm;
- Area of grassland in the immediate vicinity of the poultry farm; distance from the poultry farm to forest area;
3. Geographical location of the poultry farm in the Netherlands
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