“Risk-Based Avian Influenza Reduction” – Poultry World

In the summer of 2021, Dr. Janicki Schroeder, a veterinarian and epidemiologist at Utrecht University, received her Ph.D. in a broader approach to avian influenza prevention.

“This project is part of our general research topic here at Utrecht University focusing on infectious diseases in animals,” says Professor Arjan Stegmann, who supervised Yannick Schroeder’s PhD thesis. Stegeman heads the Department of Farm Animal Health at Utrecht University, which has been researching bird flu since 2003 when the first major outbreak of bird flu hit the Netherlands. “In that particular outbreak, the disease started as a low variant of the pathogen, causing mild illness on one farm. From there it mutated into a highly pathogenic type, and spread to large parts of the Dutch poultry industry.”

The fact that the avian influenza virus has been able to spread very quickly throughout the world since the 1990s is also due to the huge increase in the size and density of poultry farms in certain parts of the world, in the view of the professor. “Another reason is that the vaccines that are sometimes used do not protect against the spread of the virus, like the coronavirus vaccines in human medicine.”

Hazard maps with risk areas

The most worrisome form of bird flu is H5N1, a highly contagious type. According to Stegeman, the problem is that wild bird populations are becoming increasingly resistant to this virus strain because they are constantly exposed to it. When the H5 virus jumped from poultry to migratory birds in Asia for the first time, it caused major problems.

“However, as it turned out, 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 deal with migratory birds from Europe. This way these variants can spread further from Asia to Europe,” says Stegmann.

“…The bird flu virus can mutate very quickly.”

Over time, some wild birds become carriers of highly pathogenic variants. Meanwhile, there are now also other variants of H5 in circulation in wild bird populations, such as H5N2, H5N6 and H5N8. When wild birds become infected, they either die or become resistant and can serve as a reservoir from which to infect commercial domestic birds. “The course of disease in commercial poultry is so severe that they die without warning.”

Another tricky thing about the bird flu virus is that it can mutate very quickly. This is because many bird species migrate to gathering places and then infect each other. This is why one of the components of Schroeder’s research was to perform risk analyses. Dr. Fred de Boer from Wageningen Schreuder University helped create these risk maps with risk areas. Bird flu risk maps for the Netherlands have already been completed, and De Boer now plans to map risk areas in Europe as well.

“You can see on these maps where the high and low risk areas are, the areas that correlate with high or low densities of some wild bird species that are known to be good host species for highly pathogenic avian influenza viruses,” Stegmann said. It is believed that such risk maps can be used by poultry farmers, for example, to establish new farms in areas where the risk of infection from wild birds is relatively small. Governments can also use these maps to support their permit policy when evaluating new poultry projects.

The risk maps for bird flu for the Netherlands have already been completed, and Dr. Fred de Boer plans to make maps of risk areas in Europe as well. Photo: Dick Van Dorn

predictive model

To research where populations of wild birds flock together, Schroeder used data from Sovonne, the Dutch center for field ornithology. This organization collects very detailed data on the densities of bird species. Schroeder used this data to analyze the distribution of 54 species of wild birds, mainly geese and ducks, as well as birds of prey. These findings were combined with data from bird flu outbreaks between 2014 and 2018. Next, the doctoral student set up a model that allows you to predict where the risks of an outbreak will be greatest. Based on this model, a risk map was created for the Netherlands, Stegmann said, adding: “We’ve also used the model for the most recent outbreaks in 2020 and even those in 2021. It’s very cool, because you can really see the model in action.”

What also emerged from the doctoral student’s research is that some bird species sometimes transmit more viruses than others. “As shown, there are now different types of highly contagious viruses spread all over the world. However, the dominant type and how birds become sick varies from year to year. In 2020-2021 several wild geese in the Netherlands were infected with bird flu, Scavengers like birds of prey were also infected. In other years the species were different, like pigeons or tufted ducks.” This information can also be included in annual risk maps.

The professor says the fact that the model and risk maps provide a good indication of where the risk of an outbreak is greatest is helpful. However, it is still difficult to accurately predict transmission of infection from wild birds to poultry. To be able to say something about causation, you must examine 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 may also have an effect.”

future in real time

Now in the water-rich Netherlands there is an animal disease expert group advising the Dutch Ministry of Agriculture on bird flu mitigation measures. Stegmann: “The ministry is already using the risk map that emerged from our model. In addition, our research has shown that mortalities in laying hens are a very sensitive procedure for early detection of avian influenza infection, along with mortalities as well as clinical signs in meat ducks. This knowledge means that Companies and veterinarians can identify bird flu more quickly.”

As the professor notes, the research also shows how urgent the topic is and how important it is to keep a close eye on even the smallest changes in farm animal health.

It is still difficult to predict the exact transmission of infection from wild birds to poultry.  To be able to say something about causation, you must examine local conditions.  Photo: Dick Van Dorn
It is still difficult to predict the exact transmission of infection from wild birds to poultry. To be able to say something about causation, you must examine local conditions. Photo: Dick Van Dorn

Stegeman believes that it may be necessary to consider how to achieve a better spread of poultry farms around the world. Another aspect that can also be examined is where the areas of greatest danger are. For example near places where large numbers of waterfowl congregate. “Ideally, this wouldn’t be a place to start a poultry farm,” says the professor. “You should also try to prevent poultry farms from being agglomerated in other suitable places.”

If you collect all the risk indicators together on the risk maps, in principle, you can create a digital risk map in real time. Poultry farmers and governments can go to a website to check out this map and instantly see which region(s) or region(s) are currently most at risk of avian influenza. Technically, it is possible to generate dynamic, real-time risk maps of this type but the existing risk map is static and has been developed on the basis of available data, which has been aggregated over several years. Stegmann concludes that “there is still some work to be done before real-time risk estimates become available.”

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