Bird Flu Europe: Record Infections in Wild Birds

Bird flu has never affected so many wild birds in Europe as this season. This is evident from an interim report from the European Food Safety Authority (EFSA) that was published on Monday, and unpublished research from Wageningen Bioveterinary Research (WBVR) and Erasmus MC.

Since the start of this bird flu season in September, EFSA reported more than 1,400 infections among wild birds found dead. That is more than ever and even twice as much as in the same period in the disaster year 2022, when a total of 76 Dutch poultry farms had to be cleared.

Research by Erasmus MC, one of the few laboratories in Europe where live birds are also tested for the presence of the virus, also points to an exceptionally heavy bird flu season. Research leader and virologist Ron Fouchier confirms this in response to questions from NRC. A quarter of the live ducks examined in the Netherlands carry the highly contagious bird flu variant H5N1. That is the highest percentage of infected wild birds ever recorded. This mainly concerns apparently healthy, but infected ducks.

According to experts, the high number of infections increases the risk of a new flu variant that can also infect humans and would make the unvaccinated poultry sector in the Netherlands unsustainable in the long term. On Wednesday morning, the Dutch Food and Consumer Product Safety Authority (NVWA) reported new infections at three poultry farms in Limburg and Overijssel.

‘Not a good signal’

The EFSA speaks of an “unprecedented high spread” of the avian flu virus among wild birds and calls for strict measures to “prevent further spread among poultry farms.” In recent weeks, the virus has mainly been detected in ducks, geese, swans and cranes.

“It is still a bit too early to say that this is the worst bird flu outbreak to date,” said Mónika Ballmann, head of the National Avian Influenza Reference Laboratory, noting that the bird flu season usually lasts until February or March. “But it certainly doesn’t look good. The fact that the virus is already spreading so widely among wild birds, and throughout Europe, is not a good signal.”

The laboratory of Wageningen Bioveterinary Research (WBVR) in Lelystad, which examines samples of dead birds, has been scaled up to the crisis phase since October 27, with an extra number of test kits and materials. While not a single sample was positive in September, infections have skyrocketed since October 10, according to Ballmann. By mid-November, more than half of the wild birds submitted had bird flu. “It is difficult to predict what awaits us, but at the moment things are moving very quickly.”

Scientists do not yet know how the outbreak among wild birds is so serious this year. Here too, it is still very early in the season to draw clear conclusions, but there are suspicions. “The H5N1 virus variant that is now circulating is almost the same type that spread last year,” says Ballmann. “No crazy major mutations have occurred yet. This variant only differs by eight amino acids from last year’s virus. That is a very small difference, but perhaps just enough to spread better between birds.”

The composition of the wild bird population may also play a role, she thinks. “The last major outbreak in wild birds was in 2023. Every year, many young birds enter the population that have not yet built up immunity against the virus. The virus spreads very quickly among the young birds.”

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Neither stack

Germany has been the hardest hit of all European countries so far, according to EFSA figures, with 909 infections detected this season. After France, where the virus was found in 165 birds, the Netherlands follows with 78 confirmed infections. The total number of infected birds is much higher, because not all research results have yet been shared with the European Food Authority and many dead birds are never examined; if several dead birds are found in one place, only one of the animals is sent to the laboratory. “Testing is expensive and the chance that birds found together died from the same virus is very likely,” says Ballmann.

EFSA expects the number of infections to remain high in the coming weeks and spread to other areas as migratory birds continue their journey. “Unless additional measures are taken, this is likely to lead to an increase in the virus among poultry,” EFSA wrote in its report, “as well as higher mortality among wild birds and mammals.”

If mammals become infected with bird flu more often, this increases the risk of the development of a flu variant that is also dangerous to humans.

Wild ducks as dispersers

To keep a good overview of how the bird flu virus spreads among birds, but also between animal species, it is important to also check living animals for infections, says Ron Fouchier, professor of Molecular Virology at Erasmus MC. His laboratory examines about ten thousand live birds per year. Erasmus MC started this 27 years ago and intensified it when the virus reached Europe from Asia via bird migration in 2005.. “Ducks are always the first healthy birds where we find the virus. It is these types of long-distance migrants who enter the Netherlands with the virus.”

Ducks are a suitable carrier, or “vector,” of bird flu because they often survive the virus, Fouchier says. The virologist previously conducted research on six duck species, which showed that a number of species spread the virus, but are not affected by it themselves. “The best vectors can continue to migrate while carrying the virus. Other bird species immediately become very ill. We regularly see geese, swans, seagulls and terns dying in the field. The virus also jumps to poultry. We think that the source of all this misery comes from the ducks.”

‘Cleaning no longer works’

The high number of infections among wild birds poses a threat to poultry farming. Bird flu regularly enters stables, resulting in the culling of hundreds of thousands of chickens and chicks – more than a million since October 6. “The jump to commercial companies often happens this year,” says Ballmann. And she noticed something else: the virus is not clustered in hot spots, but can be found in wild birds in all corners of the country.

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Due to the high number of infections, culling birds is no longer a logical approach. “Bird flu has shifted from a seasonal problem to an ongoing problem in recent years,” says Arjan Stegeman, professor of Farm Animal Health at Utrecht University. “Infected birds are present all year round and can carry the virus with them during their migration.”

This means for poultry farming throughout Europe that we are combating this virus in a way that no longer fits with how the virus now behaves, says Stegeman. “Until ten years ago, culling was a rational approach: the virus disappeared from the stable and eventually from the country. Now that there is constant exposure from the environment, that approach no longer works.”

Foie gras

Most poultry farms that became infected in recent weeks are already operating at a high level of biosecurity, says Mónika Ballmann. And yet the virus manages to enter companies, via the droppings of infected wild birds that remain under an employee’s boots, via contaminated water, or via grass or straw that infected ducks have had contact with.

“It is most likely that the virus enters the stables through people,” says Ballmann. It is also the most important recommendation from the EFSA report: better compliance with safety measures by owners and employees of poultry farms: changing shoes and clothes, washing hands.

But if we really want to prevent infections among poultry in the future, Stegeman believes there is no other option than to vaccinate the animals en masse. Experiments are currently being conducted in the Netherlands with vaccinating poultry. In France, ducks are already being vaccinated to protect the foie gras sector. “Vaccination is of course impossible with wild birds, but you can ensure that the spread in poultry farms stops.”

“We have to get rid of this culling in the long term,” says Kees de Jong, chairman of the poultry farming department of LTO Netherlands. “Those days are behind us. The virus is in the wild birds and it will not go away.”

Vaccination is the solution, De Jong acknowledges, “but there is resistance among a very small part of the population and among trade relations in other countries to products from vaccinated animals.” But the ubiquity of bird flu is also causing a changed attitude in those countries, says De Jong. “Everything becomes fluid under pressure. In the US, for example, they were quite critical of vaccinations, but now they want to look over our shoulders to see how we are doing with the vaccine.”

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