Phenotypes of the reassortant viruses observed in this study. Credit: Nature Communications (2025). DOI: 10.1038/s41467-025-67234-1

The H5N1 avian influenza virus—commonly known as bird flu—has been causing outbreaks in dairy cows in the United States since March 2024. Now, scientists studying the adaptation of the avian H5N1 viruses to cows have found that some of the more recent variants are more able to infect cow cells and tissues than some older variants.

The study, published in Nature Communications and led by scientists at the MRC–University of Glasgow Center for Virus Research, examined a large panel of viruses representing more than 60 years of H5N1 evolution. The researchers say their findings highlight the urgent need for continued testing and monitoring, especially 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, H5N1 is known for its ability to spillover in mammals, raising concerns that it could spread further into other animal species. As the virus continues to circulate and adapt in mammals, there is a risk that new strains could emerge that are better able to infect humans. This underlines the importance of ongoing surveillance in domestic animals, including livestock.

The study showed that the ability of H5N1 viruses to infect cow cells and mammary tissue is not controlled by multiple viral genes and depends on changes that viruses have acquired gradually over time. The researchers also found that bird flu viruses vary widely in how well they can replicate in cow cells. This means some bird viruses may already be closer than others to being able to infect cattle and potentially other mammals.

Professor Pablo Murcia, from the MRC–University of Glasgow Center for Virus Research, 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."

Professor Massimo Palmarini, from both the Erasmus Medical Center and the MRC–University of Glasgow Center 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 U.S. cattle is clearly the best adapted so far, there are other bird viruses that could potentially infect cows if given the chance."

More information: Matthew L. Turnbull et al, The potential of H5N1 viruses to adapt to bovine cells varies throughout evolution, Nature Communications (2025). DOI: 10.1038/s41467-025-67234-1

Citation: Recent H5N1 bird flu variants show increased ability to infect dairy cattle (2025, December 15) retrieved 15 December 2025 from https://phys.org/news/2025-12-h5n1-bird-flu-variants-ability.html

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