A dairy cow in the Netherlands appears to have been infected with H5N1, with antibodies to the virus detected in its milk.

 It’s the first report of this virus having spread to cattle outside of the United States.

The All Ireland Science Media Centre asked experts to comment.

Dr Connor Bamford, Lecturer, School of Biological Sciences and The Institute for Global Food Security, Queen’s University Belfast, comments: 

“There are reports of evidence that a cow has been infected with avian influenza in Europe (Netherlands). There is no sign that this is an immediate risk for people or animals given that it was likely an old infection in the past and no sign of active infection was found.

“This is concerning off the back of a serious epidemic of avian influenza in cattle in the USA that has persisted for years and retains capacity to infect and cause disease in people, thus, representing a potential human pandemic risk.

“One main question is whether this was a US-specific phenomena. There are several bits of evidence to say that this is not specific to the US. This evidence now includes detection of cow infections in Europe. The UK has previously found a sheep infected with avian influenza.

“Given that the island of Ireland is at continuous risk of avian influenza, and that we have a high density of cattle, these results reinforce the importance of i) preventing spillover of the virus from birds to cows; and ii) being able to detect and monitor infections if they do occur. Currently, neither of these are really being undertaken in Ireland.”

Declaration of interest: None

Dr Gerald Barry, Assistant Professor of Virology & Deputy Director of the One Health Centre, University College Dublin, comments: 

Why haven’t we seen evidence of infection of cattle with H5N1 outside the US until now?

“There are a number of possible reasons for this. Firstly, in a lot of cases the clinical signs in cattle are mild / non-existent so although infections may be occurring, we may not detect them. Routine testing of cattle for avian influenza has been restricted or hasn’t been carried out at all in a lot of countries so we wouldn’t necessarily know if it was there – a lot of countries take an approach of only testing for something is there is a clinical justification for it i.e. if the animal is sick in some way.

“The case in the Netherlands seems to have been detected because a cat on the farm was sick and tested positive and so the other animals were tested. Similarly, a case of a positive sheep in the UK in 2025 was only tested because birds in close proximity to the sheep were sick and tested positive. Alongside that, factors such as breed differences, farming practice differences and the prevalence of the circulating virus itself may all be contributing to a lack of outbreaks outside of America.”

How likely is something similar to happen on the island of Ireland, and are current surveillance and biosecurity measures sufficient?

“There is no clinical reason to suspect that cattle are currently being infected by avian influenza, but the possibility of it occurring in the future can not be ruled out.

“In Ireland currently there is a study ongoing within the Department of Agriculture, Food and the Marine (DAFM), testing blood samples from cattle collected a couple of years ago for the presence of avian influenza antibodies. This is a retrospective study to see if those animals were positive and will provide a look back to see if cattle before now are likely to have been infected. Results from this study are expected later this year.

“Live cattle on farms today are not routinely tested for avian influenza or antibodies to avian influenza. If there is a clinical reason, DAFM can rapidly test samples if needed. Because animals can be infected without obvious sickness and can potentially spread that to other animals and humans, there is a risk that cases might be missed, so improved surveillance in this scenario would be beneficial.

“Both the EU, through a project called OH-ALLIES and DAFM are collaborating with University College Dublin, University of Galway and others to improve this national surveillance so any outbreaks that might occur will be identified rapidly.”

What does finding antibodies (but no active virus) in a cow tell us about risk of future outbreaks in cattle?

“Finding antibodies rather than active virus means that the animal was infected sometime in the recent past but the infection was not detected at the time. Farmers are generally very aware of how their cattle are in terms of their day to day health so it suggests that the animal that was infected wasn’t obviously sick. This means that infection has occurred silently. The risk with this is that it means that in future outbreaks, the virus could circulate in a herd and even pass to humans without detection, until it reaches a host that gets very sick (human or animal). Silent circulation also increases the likelihood of virus adaptation to mammalian hosts, thus increasing the likelihood of spillover into human populations.

“The ability of the virus to circulate silently also indicates that only testing for the virus in cattle when animals show signs of sickness is not enough, broad spectrum testing of herds should become part of a national One Health surveillance plan for Ireland and the EU and it should be focussed on areas where the risk is highest, like areas where wild birds that carry the virus tend to congregate or where surveillance has indicated that the virus is circulating in wildlife.

“Better surveillance will improve our ability to detect outbreaks early, thus helping to protect both animal and human populations more effectively.”

Declaration of interest: None received