In the summer of 2021, Dr. Janneke Schreuder, veterinarian and epidemiologist at the University of Utrecht, obtained her doctorate on a broader approach to the prevention of avian influenza.
“This project is part of our general research theme here at Utrecht University which focuses on infectious diseases in animals,” explains Professor Arjan Stegeman, who supervised Janneke Schreuder’s doctoral thesis. Stegeman chairs the Farm Animal Health division at Utrecht University, which has been conducting bird flu research since 2003, when the first major bird flu epidemic hit the Netherlands. “In this particular outbreak, the disease started as a low pathogenic viral variant, causing mild illness on a farm. From there it mutated into a highly pathogenic variant, spreading to large parts of the Dutch poultry industry.
The fact that the bird flu virus has been able to spread so rapidly around the world since the 1990s is also due to the huge increase in the scale and density of poultry farming in some parts of the world, according to the teacher. “Another reason is that the vaccines sometimes used do not protect against the spread of the virus, much like coronavirus vaccines in human medicine.”
Risk maps with risk areas
The bird flu variant of greatest concern is H5N1, a highly pathogenic variant. The problem, according to Stegeman, is that wild bird populations have become increasingly resistant to this viral strain because they are constantly exposed to it. When the H5 virus passed from poultry to migratory birds in Asia for the first time, it caused significant problems.
“However, it turned out that over time, wild birds did not always die immediately after infection, allowing selection of variants that could persist in these populations. In breeding areas, in Siberia for example, Asian migratory birds come into contact with migratory birds from Europe. This way, these variants could spread further from Asia to Europe,” says Stegeman.
“… the bird flu virus can mutate very quickly.”
Over time, some wild birds have become carriers of highly pathogenic variants. Meanwhile, there are now other H5 variants circulating in wild bird populations, such as H5N2, H5N6, H5N8. When wild birds are infected, they either die or become resistant and can serve as a reservoir from which commercial poultry can become infected. “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. Indeed, many species of birds migrate to gathering places and then become infected. This is why one of the components of Schreuder’s research was to perform risk analyses. Dr. Fred de Boer of Wageningen University helped Schreuder create these risk maps with risk areas. The bird flu risk maps have already been completed for the Netherlands and De Boer now plans to map the risk areas for Europe as well.
“You can see on these maps where the high and low risk areas are, areas associated with high or low densities of certain wild bird species known to be good host species for highly pathogenic influenza viruses. avian,” said Stegeman, who believes these risk maps could be used by poultry farmers, for example to establish new farms in areas where the risk of infection from wild birds is relatively low. Governments could also use these maps to support their licensing policy when evaluating new poultry projects.
To research where wild bird populations congregate, Schreuder used data from Sovon, the Dutch Center for Field Ornithology. This organization collects very detailed data on the densities of bird species. “Schreuder used this data to analyze the distribution of 54 species of wild birds, mainly geese and ducks, as well as raptors. These results were combined with data from avian flu epidemics between 2014 and 2018. Subsequently, the doctoral student created a model that predicts where the risk of an epidemic is highest. Based on this model, a risk map was drawn for the Netherlands,” Stegeman said, adding, “We also used the model for the latest epidemics in 2020 and even those in 2021. Very fascinating, because then you can really see the model at work.”
What also emerges from the research of the doctoral student is that certain species of birds sometimes transmit more viruses than other species. “As noted, there are now various variants of highly pathogenic viruses circulating around the world. However, the dominant type and how birds become sick varies from year to year. In 2020-2021, many wild geese in the Netherlands were infected with bird flu, as were scavengers, such as birds of prey. In other years, it was different species, such as ducks or tufted ducks. This information can also be included in annual risk maps.
The fact that the model and the risk maps provide a good indication of where the risk of an outbreak is highest is helpful, says the professor. “However, it is still difficult to predict the exact transfer of infection from wild birds to poultry. To be able to say anything about causation, one would have to look at the local conditions: the landscape, the actual presence of migratory and resident wild birds, and whether they are infected. Movements of people and the role of mice, rats or other animals, for example, around poultry farms can also have an influence.
Future in real time
In the water-rich Netherlands, there is now an animal disease expert group that advises the Dutch Ministry of Agriculture on bird flu mitigation measures. Stegeman: “The ministry is already using the risk map from our model. In addition, our research has shown that mortality in laying hens is a very sensitive measure for the early detection of avian influenza infections, as well as mortality in combination with clinical signs in meat ducks. This knowledge means businesses and vets can recognize bird flu more quickly.
As the professor notes, the research also shows how urgent the topic is and how important it is to closely monitor even the smallest changes in animal health on a farm.
Stegeman thinks it may be necessary to consider how a better distribution of poultry farms around the world can be achieved. Another aspect that could also be looked at is where the highest risk areas are. For example near places where large numbers of waterfowl congregate. “Ideally, it wouldn’t be a place to start a poultry farm,” says the professor. “You should also try to prevent an agglomeration of poultry farms in other suitable places.”
If you put all the risk indicators on risk maps, in principle, you could create a real-time digital risk map. Poultry farmers and governments could go to a website to check this map and immediately see which area(s) or region(s) are currently most at risk of bird flu infection. Technically, it is possible to create such dynamic risk maps in real time, but this risk map is static and was established on the basis of available data, pooled over several years. “So there is still work to be done before real-time risk estimates are available,” Stegeman concludes.