'Dog flu' is growing into a virus that could creep into infecting humans, scientists have warned.
The contagious respiratory disease first infected dogs in around 2006 and is a mutated form of a particular type of bird flu known as H3N2.
Since then, it has continued to evolve and researchers are concerned that it is now better at recognising human cells.
It means the virus could be one step closer to beating the hurdles that stopped it infecting people.
In a study, a team at the China Agricultural University in Beijing looked at swabs from more than 4,000 dogs.
The findings revealed that the virus is now showing signs of being able to spot human cell receptors and spread in human cells.
Researchers said that dogs may serve as an 'intermediate' for bird flu to adapt into something that could infect people.
However, so far there has not been a single case reported among humans worldwide.
Professor Ian Jones, who teaches virology at the University of Reading, said the research is proof that the virus is "creeping" towards being able to infect people.
"It's a data-rich paper that surely shows that the most recent viruses are more adapted to mammals than was the original virus that made the leap from an avian," he said.
"But some of this is just the virus settling down in the dog, so inevitably becoming mammalian virus-like."
The professor ended by pointing out that "the case for a threat is not clear."
The study looked at results from six dogs that were intentionally infected with the known canine flu strains of H3N2.
Each dog fell mildly unwell, with the most serious symptoms including a fever, sneezing and coughing.
However, scientists raised concerns that the study shows the "longer term pandemic potential" threat H3N2 now poses to people.
Professor James Wood, head of veterinary medicine at the University of Cambridge, said "it is pretty clear" the bird flu H3 strain had become a dog-specific virus.
"The changes in the canine virus apparently are making it better adapted to transmit within mammals, as you might expect after such a long period in dogs," he told The Telegraph.
"The virus does not seem to pose particularly worrying health threats to dogs - one might be more concerned about the longer term pandemic potential in other species such as humans."
The H3N2 strain is different to H5N1 which was behind the world's biggest ever bird flu outbreak and sparked fears of a fresh pandemic post Covid.
