Does Canine Influenza Pose a Human Health Risk?

Although there have been no reports of the 'dog flu' in humans, scientists are concerned about the potential for canine influenza viruses to mutate and pose a risk to human health.

A mysterious respiratory illness among dogs has made headlines recently, with more than a dozen states reporting cases of what experts call "atypical canine infectious respiratory disease." Moreover, researchers have been unable to identify the cause of this novel canine sickness.

The new and mysterious canine respiratory disease comes on the heels of recent surges in canine influenza. Most recently, Wake County Animal Shelter in North Carolina closed for over a month to contain a canine influenza outbreak. Still, experts say the mystery illness is inconsistent with canine influenza or other diseases such as kennel cough.

With the recent rise in dog influenza and atypical canine infectious respiratory disease, researchers are becoming increasingly concerned about the potential for dog-specific influenza A viruses to infect people.

It's already well known that animal-origin influenza viruses have the potential to change and transmit to humans. For example, the virus responsible for the 2009 H1N1 pandemic contained gene segments from human, swine, and bird influenza A viruses.

But could canine influenza become the next pandemic?

What is canine influenza?

Canine influenza, AKA the dog flu, is a respiratory illness caused by two viruses — influenza A H3N8 and H3N2. Dogs inflicted with the disease may experience cough, runny nose, fever, and lethargy. The severity of the illness ranges, with some animals showing no symptoms and others becoming seriously ill with pneumonia.

According to the CDC, canine influenza H3N8 originated in horses, and H3N2 originated in birds before infecting dogs. Both viruses have adapted to canines and are mostly considered canine-specific despite reports that dogs have transmitted H3N2 to cats.

Can canine influenza viruses jump to humans?

The Centers for Disease Control and Prevention (CDC) says that no evidence indicates H3N8 or H3N2 have spread from dogs to people, and there have been no reports of human cases. Still, the agency points out that it's possible for canine influenza viruses to mutate and infect other mammals, including people.

While avian and swine flu viruses have genetic diversity, which makes them more likely to mutate into variants that can infect humans, canine influenza viruses have remained genetically stable and can only infect dogs or sometimes cats.

However, in a 2018 study published in mBio, Chinese scientists found evidence that canine influenza viruses are becoming more genetically diverse. Specifically, they found two influenza A viruses that recently "host switched" from pigs to dogs in southern China. One of those viruses has the potential to become zoonotic, meaning it could jump from animals to people.

Adolfo Garcia-Sastre, Ph.D., corresponding author and director of the Global Health and Emerging Pathogens Institute at the Icahn School of Medicine, commented on the study, saying, "The majority of pandemics have been associated with pigs as an intermediate host between avian viruses and human hosts. In this study, we identified influenza viruses jumping from pigs into dogs. We now have H1N1, H3N2, and H3N8 in dogs. They are starting to interact with each other."

More recently, a study published earlier this year in eLife revealed that during adaptation in dogs, H3N2 canine influenza viruses gained the ability to recognize the human-like SAα2,6-Gal receptor and showed an increase in the ability to replicate in human airway cells.

Because no one knows for sure whether canine influenza viruses could eventually become a threat to humans, the CDC conducted a 2016 risk assessment using the Influenza Risk Assessment Tool to examine the pandemic potential of canine H3N2. The agency found this specific virus posed a low risk.

In addition, the World Health Organization's global surveillance system continues to monitor for potential threats to human health posed by H3N8, H3N2, and other animal-specific influenza A viruses.


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