Across the Species: Dogs at Risk for Mutating Equine Influenza Virus

If equine influenza can jump from horses to dogs, will humans be next?

Horses and dogs (including hounds like these) share our affections. Might they also share our infections? And we share theirs? Interesting research puts dogs at the middle of an interspecies viral exchange. (Thanks to Karen Roe for her lovely photo of the historic stables at Audley End in England.)

Who thinks about dog flu? You probably haven’t given it much thought, but when an outbreak hit my town here in Massachusetts last month, we were all Google-ing for more information.

Dogs at a local doggie-daycare center were affected, and it made all of us in the area curious–and concerned–about the disease. The Massachusetts Division of Animal Health was concerned enough to issue an alert.

The H3N8 virus, as canine influenza is known, didn’t result in a mass outbreak, but a lot more dog owners will opt for the vaccine now. And when some new research was announced last week about the crossover of influenza virus between horses and dogs, I thought I’d share this news, which is to be published by the Journal of Virology.

You may be surprised to learn where canine influenza had its start.

In a nutshell, it seems that equine influenza viruses from the early 2000s can easily infect the respiratory tracts of dogs, while those from the 1960s are only barely able to cross over.

The research paper, “Infection and pathogenesis of canine, equine and human influenza viruses in canine tracheas”, also suggests that canine and human influenza viruses can mix, and generate new influenza viruses. 

Canine influenza is a relatively new disease. The first appearance is believed to have been in 2003, as a result of direct transfer of a single equine influenza virus to dogs in a large greyhound training facility. It was subsequently carried to many states by the infected greyhound, say the researchers.

Similar transfers have occurred among foxhounds in the UK, and in dogs kept near infected horses during a 2007 outbreak in Australia, they report. 

In the study, investigators from the United States and the United Kingdom infected dog tracheal explant cultures—essentially pieces of a dog’s windpipe cultured in the laboratory to mimic the cellular complexity and the physiology of the host—with canine influenza virus, equine influenza virus, and human influenza virus. 

They then compared the growth of the viruses, and the damage they wrought.

Equine influenza virus from 2003 caused an infection much like that from canine influenza virus in terms of the virus’s rate of replication 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,” says corresponding author Pablo Murcia of the University of Glasgow Centre for Virus Research in the UK. That, he says, means 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 underway. 

Many people thought that the Australian authorities over-reacted when the Equine Influenza outbreak sickened so many horses in that country in 2007. But research like this provides evidence that the diseases we are fighting in our horses are not the same ones that our grandparents fought in their horses.

The soup of viruses out there is infinite. Dogs, horses and people are together all the time, but let’s not forget bird flu and swine flu and other flus we don’t even know about. They’re fascinating to study–and essential to avoid.

Publication note: The manuscript describing the research can be found online. The final version of the article is scheduled for the August 2014 issue of the Journal of Virology


  1. G. Gonzalez, J. F. Marshall, J. Morrell, D. Robb, J. W. McCauley, D. R. Perez, C. R. Parrish, P. R. Murcia. Infection and pathogenesis of canine, equine and human influenza viruses in canine tracheas.Journal of Virology, 2014; DOI:10.1128/JVI.00887-14




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