migratory birds from Europe. In this way those variants could spread further from Asia to Europe”. Over time, some wild birds became carriers of the highly pathogenic vari- ants. Meanwhile, there are now also other H5 variants in cir- culation in wild bird populations, such as H5N2, H5N6, H5N8. When wild birds are infected, they either die or they become resistant and can act as a reservoir from which commercial poultry can be infected. Stegeman: “The course of the disease in commercial poultry is so acute that they succumb without warning”. Another tricky thing about the bird flu virus is that it can mutate very quickly. This is because many bird species mi- grate to gathering places and then infect each other. That is why one of the components of Schreuder’s research was to perform risk analyses. Dr Fred de Boer of Wageningen Uni- versity helped Schreuder with making these risk maps with risk areas. The risk maps for bird flu have already been com- pleted for the Netherlands and De Boer is now planning to map the risk areas for Europe, too. Stegeman: “You can see on these maps where the high and low risk areas are, areas which are associated with high or low densities of certain wild bird species that are known to be good host species for
highly pathogenic avian influenza viruses”. Stegeman be- lieves that these risk maps could be used by poultry farm- ers, for example, to establish new farms in areas where the risk of infection from wild birds is relatively small. Govern- ments could also use these maps in support of their permit policy when assessing new poultry projects.
Predictive model For research into where wild bird populations flock together, Schreuder used data from Sovon, the Dutch Centre for Field Ornithology. This organisation collects very detailed data on the densities of bird species. Stegeman: “Schreuder used this data to analyse the distribution of 54 wild bird species, main- ly geese and ducks, as well as birds of prey. These results were combined with data from bird flu outbreaks between 2014 and 2018. Subsequently, the PhD student made a model that allows you to predict where the risks of an outbreak are greatest. Based on that model, a risk map was made for the Netherlands”. He adds: “We also used the model for the latest outbreaks in 2020 and even those in 2021. Very fascinating, because then you can really see the model at work”. What also emerged from the PhD student’s research is that
▶ POULTRY WORLD | No. 1, 2022
Arjan Stegeman: “Technically it is possible to create dynamic, real- time risk maps. So there is still some work to be done be- fore real-time risk estimates become available”.
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