Bird flu virus adapting to infect cows, scientists warn

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Scientists in Glasgow have found that some strains of the H5N1 avian influenza virus, commonly known as bird flu, are becoming better at infecting cows.

The development is raising concerns about the virus’s potential to spread further in mammals.

Researchers have found that more recent variants can infect cow cells and tissues more effectively than older strains.

The findings come from a study published in Nature Communications, led by scientists at the MRC–University of Glasgow Centre for Virus Research. The team analysed a large panel of viruses representing more than 60 years of H5N1 evolution.

Professor Pablo Murcia said: “Influenza viruses are constantly changing and this rapid evolution allows them to infect new animal species.

“The better adapted they become to infect mammals, the more chances they have to infect and adapt to humans – as we saw with the 2009 swine flu pandemic.”

The H5N1 virus has been causing outbreaks in dairy cows in the United States since March 2024.

But researchers say the latest results highlight the urgent need for continued testing and monitoring as the virus continues to spread in dairy cattle and remains a potential pandemic threat.

The discovery of H5N1 in cows in spring 2024 came as a major surprise, as flu viruses were not previously thought to cause outbreaks in cattle. However, bird flu is known for its ability to spill over into mammals, raising concerns it could spread into other animal species.

As the virus continues to circulate and adapt in mammals, scientists warn there is a risk that new strains could emerge that are better able to infect humans.

The study found that the ability of H5N1 viruses to infect cow cells and mammary tissue is not controlled by a single factor, but depends on changes acquired gradually over time.

Researchers also discovered that bird flu viruses vary widely in how well they can replicate in cow cells.

Professor Massimo Palmarini, from both the Erasmus Medical Centre and the MRC–University of Glasgow Centre for Virus Research, added: “Our work shows that different bird flu viruses have very different abilities to infect cow cells and tissues.

“While the strain currently spreading in US cattle is clearly the best adapted so far, there are other bird viruses that could potentially infect cows if given the chance.”

The study, The potential of H5N1 viruses to adapt to bovine cells varies throughout evolution, was funded by the UKRI Medical Research Council, Wellcome, and the UKRI Biotechnology and Biological Sciences Research Council.