First case of avian influenza antibodies in cow in Europe

The reason for this investigation was the detection of avian influenza (Avian influenza, HPAI H5N1) in a cat. The cat was submitted for testing by the veterinarian, who suspected it might have avian influenza. The infected cat originated from a dairy farm in Friesland, a province in the Netherlands. This prompted further investigation into the possible presence of avian influenza in the dairy cattle on this farm.
Initially, 20 out cows were sampled. Individual milk samples and a bulk tank milk sample were analysed for the presence of avian influenza virus (test method: PCR) as well as for the presence of antibodies against the avian influenza virus (test methods: ELISA and Luminex). No virus was detected in any of the animals. In one cow, antibodies against the H5N1 avian influenza virus were detected.

Antibodies against the avian influenza virus were detected in this cow. This means the cow has had a viral infection caused by the avian influenza virus.
It is known that this cow had mastitis a few weeks ago (mid-December) and that her milk production decreased. These symptoms are consistent with an avian influenza virus infection in dairy cattle. No samples were collected during the period when the cow was ill, meaning that no virus could be detected. As a result, the link between the clinical signs in December and an avian influenza infection at that time cannot be established with certainty.

Following the serological confirmation of a previous infection in this one cow, the Netherlands Food and Consumer Product Safety Authority (NVWA) sampled all lactating animals on the farm. Both milk and blood samples were collected from the animals. These samples are being tested at Wageningen Bioveterinary Research for the presence of avian influenza virus and/or antibodies against the virus. The results of the PCR tests show none of the animals carries the virus. Detecting antibodies (ELISA) takes more time. Results of these tests will become available shortly.

It is known that avian influenza can occur in mammals. The virus is increasingly being found in mammals, although this usually involves predators such as foxes or cats. They may become infected, for example, by eating dead infected birds.

At this time, we cannot confirm or rule out a direct link between the infection in the cat and the cow on the same farm. The infections may have occurred independently, for example through exposure to wild birds in the environment (for instance if the cat ate a dead or sick wild bird). It is still likely that wild birds are the source of infection in these cattle. They may have been exposed to the droppings of infected birds, had direct contact with an infected bird carcass, or a virus-carrying bird carcass may have come into contact with the cattle feed. It is also possible that the cat became infected by consuming infected milk from the cow.

This is the first time antibodies against the avian influenza virus have been found in cattle in the Netherlands. This has also not previously been reported in Europe. In March 2025, avian influenza was detected in a sheep in the United Kingdom. In an earlier screening study on avian influenza on Dutch dairy farms (2022–2024), no antibodies against the virus were detected.

On dairy farms located in the immediate vicinity of a poultry farm infected with avian influenza, milk samples are taken as part of standard virus monitoring put in place by the Dutch government. These samples are tested for the presence of avian influenza virus and antibodies against avian influenza.

The current situation in the Netherlands is not comparable to that in the United States, because no virus particles have been found so far in the milk or in the animal itself in Dutch dairy cattle.

In cases of avian influenza infection in dairy cows in the United States, virus particles were detected in the milk of infected cattle. This means the animals were shedding the virus. In particular, milk poses a risk for transmission to other animals and potentially also to people who come into contact with infected animals or raw milk.

The Dutch dairy cow in which antibodies against the avian influenza virus were detected is not (any longer) carrying the virus and is currently not shedding virus either (the PCR test in this cow was negative). Antibodies against the avian influenza virus were detected in the cow’s milk. This means the cow has had a viral infection as a result of avian influenza virus infection. It is known that this animal was ill a few weeks ago (mid-December), also had mastitis, and that her milk production decreased. These symptoms are consistent with a viral infection such as avian influenza can cause. That is why we conduct follow-up testing in all cows on this farm to determine whether transmission between animals has occurred.

From our own research, we know that the European avian influenza virus is capable of infecting bovine respiratory epithelial cells (see: H5N1 avian influenza virus replicates in bovine respiratory epithelial cells - WUR). Research by, among others, the FLI in Germany has shown in animal studies that cattle can become ill from the European avian influenza virus and that the virus can also replicate in these animals.

In the current case, no virus was detected in the cow, only antibodies against the virus. To detect potential zoonotic adaptations in the genetic material of the virus, the virus itself is needed; such adaptations cannot be identified based on antibodies.

Yes. If there are sufficient virus particles in the milk, the virus can be detected using PCR analysis. However, if the number of animals carrying the virus is limited (for example only 1 or 2 animals on a large farm), the concentration of virus particles in the bulk tank milk sample may be too low (or too diluted) to be detected in analyses.

The hygiene measures taken (teat disinfection, cleaning of the milking cluster) help to prevent or limit transmission of the virus, but can never completely rule out virus transmission. Milk splashing may also potentially lead to virus transmission in the milking parlour, both from cow to cow and from cow to human (milker).

The likelihood is very small. Dutch milk is pasteurised before it reaches consumers. This treatment destroys the avian influenza virus. See also the advice of the Office for Risk Assessment & Research (BuRO): BuRO advice on the risks of HPAIV in milk | Risk assessment | NVWA

The European Food Safety Authority (EFSA) states that, to date, there is no convincing evidence that the avian influenza virus can be transmitted to humans through eating or drinking contaminated food (see also: Avian influenza | EFSA).

On poultry farms where dairy cattle are also kept, checks are routinely carried out for possible infection in the dairy cattle after HPAI has been confirmed in poultry. To date, analyses have not detected virus particles in the dairy cows in any case.

More information can be found on the NVWA website (in Dutch): Wat doet de NVWA tegen vogelgriep? | Vogelgriep | NVWA
And the page (in Dutch) What happens on an infected premises

The vaccines currently being tested have been developed against the avian influenza virus that is currently circulating in Europe. Vaccine efficacy is being tested in poultry (laying hens, turkeys, ducks). The first results are positive. The vaccine is not being tested in other animal species, because both vaccines are based on a so-called HVT vector that is specific to birds. These are not effective in mammals.

HPAI H5N1 is a zoonosis, a virus that can be transmitted from animals to humans. In humans, infection can cause mild to severe illness, such as red eyes, fever, coughing and pneumonia; in rare cases it can lead to death. To date, no human infections have been detected in the Netherlands.

The current risk of HPAI to public health is considered low. People who have frequent contact with animals or raw animal products, such as milk, are at higher risk of infection. It is important to prevent human infection as much as possible, as the virus could undergo adaptations (through mutation) that would allow it to spread more easily between people. No such cases are known to date.