Scientists in China have identified strains of the influenza A-H3N2 virus circulating in dogs that might be gaining the capacity to spill over into humans.
Influenza-A viruses in animal reservoirs have repeatedly crossed species barriers to infect humans. H3N2 avian influenza or bird flu viruses were first transmitted to dogs around 2006 and have since formed stable canine lineages.
A team from the China Agricultural University analysed swabs from more than 4,000 dogs.
The findings, published in the journal eLife, showed that the H3N2 canine influenza viruses (CIVs) can recognise the human-cell receptors and hold the potential to replicate in humans.
"We found that, during adaptation in dogs, H3N2 CIVs became able to recognise the human-like receptor, showed gradually increased hemagglutination (HA) acid stability and replication ability in human airway epithelial cells," they wrote in the paper.
Further, they found that "human populations lack immunity to H3N2 CIVs, and even preexisting immunity derived from the present human seasonal influenza viruses cannot provide protection against H3N2 CIVs".
"Our results showed that canines may be intermediates for adapting avian influenza viruses to humans. Continuous surveillance coordinated with risk assessment for CIVs is necessary," the researchers said.
To evaluate the infectivity and transmission ability of H3N2 CIVs in dogs, the team deliberately inoculated six dogs with the known dog flu strains.
The dogs became mildly ill, with the most severe symptoms including fever, sneezing, wheezing, and coughing.
While so far, there is no human infection reported with the H3N2 CIVs, the team cautioned that "dogs might increase the opportunity of viral cross-species transmission to humans".
According to experts, the research highlights pet dogs' role as a possible "patient zero" for a future dog flu outbreak, The Telegraph reported.
It is "pretty clear" the bird flu H3 strain has become a dog-specific virus, Prof James Wood, the head of the department of veterinary medicine at the University of Cambridge, was quoted as saying.
"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 noted.
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