Gene-editing techniques have been developed to identify and change parts of chicken DNA that could limit the spread of the bird flu virus in the animals.

Researchers were able to restrict – but not completely block – the virus from infecting chickens by altering a small section of their DNA.

The birds showed no signs that the change in their DNA had any impact on their health or well-being.

The findings are an encouraging step forward, but experts highlight that further gene edits would be needed to produce a chicken population that cannot be infected by bird flu – one of the world's most costly animal diseases.

Scientists bred the chickens using gene-editing techniques to alter the section of DNA responsible for producing the protein ANP32A.

During an infection, flu viruses hijack this molecule to help replicate themselves.

When the ANP32A gene-edited chickens were exposed to a normal dose of the H9N2 strain of avian influenza virus, 9 out of 10 birds remained uninfected and there was no spread to other chickens.

The team, from the University of Edinburgh, Imperial College London, and the Pirbright Institute, then exposed the gene-edited birds to an artificially high dose of avian influenza virus to further test their resilience.

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When exposed to the high dose, half of the group (5 out of 10 birds) became infected. However, the gene edit did provide some protection, with the amount of virus in the infected gene-edited chickens much lower than the level typically seen during infection in non-gene-edited chickens.

The gene edit also helped to limit the onward spread of the virus to just one of four non-gene-edited chickens placed in the same incubator. There was no transmission to gene-edited birds.

The study highlights the importance of responsible gene editing and the need to be alert to the risks of driving viral evolution in unwanted directions if complete resistance is not achieved, experts say.

Bird flu is a major global threat, with a devastating impact on both farmed and wild bird populations.

In the UK alone, the current outbreak of bird flu has decimated seabird populations and cost the poultry industry more than £100 million in losses.

In rare instances, mutations in the bird flu virus allow it to infect people and cause serious illness. Scientists say efforts to control the spread of the disease are urgently needed.

The study’s principal investigator Professor Mike McGrew, from the University of Edinburgh’s Roslin Institute, said: "Vaccination against the virus poses a number of challenges, with significant practical and cost issues associated with vaccine deployment," he said.

"Gene-editing offers a promising route towards permanent disease resistance, which could be passed down through generations, protecting poultry and reducing the risks to humans and wild birds.

"Our work shows that stopping the spread of avian influenza in chickens will need several simultaneous genetic changes."