In the stop-motion film Isle of Dogs what makes the threat of canine influenza lose its bite is the fact that, in real life, there’s no evidence of the flu passing from dogs to people. The general idea is that viruses that evolved to target dogs can’t infect humans — unless the genes that govern infectivity mutate. In a new study, however, scientists warn that human infection via canine influenza is a dangerous possibility and one that could lead to an outright pandemic.

On Tuesday in mBio a collaborative team of American and Chinese scientists explain that while dog flu hasn’t jumped from dogs to people yet, the fact that influenza has become increasingly diverse in canines severely increases that chance. Previously, it was accepted that dogs could become sick from two versions of Type A influenzas: H3N8 and H3N2. Now H1N1 has been identified in dogs — the same virus that drove a 2009 pandemic.

“In our study, what we have found is another set of viruses that come from swine that are originally avian in origin, and now they are jumping into dogs and have been re-assorted with other viruses in dogs,” study co-author and Mount Sinai professor of microbiology Adolfo García-Sastre, Ph.D. explained in a statement released Tuesday. “We now have H1N1, H3N2, and H3N8 in dogs. They are starting to interact with each other.”

This interaction, he elaborates, “is very reminiscent of what happened in swine ten years before the H1N1 pandemic.”

canine influenza
As of now, canine influenza viruses are thought to pose a low threat to people.

Pandemic influenzas root when viruses jump from animal populations to humans without prior exposure to the virus. The lack of exposure means that people lack immunity and are more vulnerable to disease. The majority of pandemics, García-Sastre explains, have been “associated with pigs as an intermediate host between avian viruses and human hosts.”

Now, influenza viruses are jumping from pigs to dogs. In the study, García-Sastre and his team sequenced the complete genomes of 16 influenza viruses obtained from dogs living in the Guangxi region of China. These viruses were primarily collected from pet dogs who were diagnosed with respiratory symptoms at veterinary clinics. (Although, in the statement the scientists note that many dogs in this region live on the street, which creates a more complex ecosystem for canine influenza virus transmission).

Within these dog genomes, the scientists discovered genomes that contained segments from influenza lineages that typically circulate in Chinese pigs: North American triple reassortant H3N2, Eurasian avian-like H1N1, and pandemic H1N1. Importantly, they realized that the H1N1 viruses mutated and mixed with viruses that already existed in the dogs, a process that produced the canine influenza virus genotypes.

“The new virus we have identified in our study is H1N1, but it comes from swine and is of avian origin, so it is different antigenically from the new H1N1s that were seen in the pandemic and a different origin as the previous H1N1 seen in humans,” García-Sastre.

H1N1, H3N2, and H3N8 are now identified in dogs.

Now that scientists have this knowledge, the game plan is divided into two parts: brainstorm how to restrict the circulation of the influenza virus and organize studies aimed at studying whether or not humans have any existing immunity against H1N1.

Protecting human populations from animal influenzas has typically come down to eliminating that interaction. For example, avian flu in the United States is a rarity because when its detected in poultry, they are culled from circulation. Scientists have previously attempted to restrict the spread of pig influenza through vaccination: In this study, the researcher note that the same could be tried for dogs. As of now vaccines are available to protect dogs against H3N8 and H3N2, but not H1N1.