Researchers have shown the growing ease with which equine influenza can infect dogs.
The scientists found that equine flu viruses from the early 2000s can easily infect the respiratory tracts of dogs, while those from the 1960s are only barely able to.
The research also suggests canine and human influenza viruses can mix, and generate new influenza viruses.
The research has been published ahead of print in the Journal of Virology.
Canine influenza is a relatively new disease. The first appearance is believed to be in 2003, as a result of direct transfer of a single equine influenza virus to dogs in a large greyhound training facility in the US. It was subsequently carried to many states by the infected greyhound.
Similar transfers have occurred among foxhounds in Britain and in dogs kept near infected horses during the 2007 outbreak in Australia, they report.
In the study, investigators from the United States and Britain infected dog tracheal explant cultures — essentially pieces of trachea cultured in the laboratory to mimic the cellular complexity and the host physiology of the host — with canine influenza virus, equine influenza virus, and human influenza viruses.
They then compared the growth of the viruses, and the damage they wrought.
Infection of equine influenza virus from 2003 caused an infection much like that from canine influenza virus in terms of the rate of replication of the virus and the extensive tissue damage it caused.
In contrast, viruses from 1963 replicated poorly, and caused relatively minor lesions in comparison with the 2003 virus.
The investigators also transfected cells with DNA containing the genes of both canine and human influenza viruses, to determine whether the genes from the two viruses were compatible with each other.
“We showed that the genes are indeed compatible, and we also showed that chimeric viruses carrying human and canine influenza genes can infect the dog tracheas,” said one of the study authors, Pablo Murcia, of the University of Glasgow Centre for Virus Research in Britain.
That, he said, meant that such chimeric viruses might occur naturally, and would likely be able to infect dogs.
These findings have significant implications because they show that dogs might act as “mixing vessels” in which novel viruses with pandemic potential could emerge.
Studies investigating whether they could infect human lungs are under way.
The research can be found online here. The final version of the article is scheduled for the August 2014 issue of the Journal of Virology.