The Stealth Threat Facing Dogs Around the World

flu pandemic from dogs

Story at-a-glance -

  • Dogs have long been considered to carry only one or two influenza A viruses that don’t typically pose a threat to humans
  • Researchers sequenced the genomes of 16 influenza viruses obtained from dogs in Southern China and revealed the flu viruses contained segments from three lineages known to exist in Chinese pigs
  • Flu viruses are known to jump from pigs to people with ease, and it’s possible that canine influenza viruses that originated in pigs could mutate and jump to people
  • No cases of humans being infected with canine flu have been reported

By Dr. Karen Shaw Becker

Flu viruses are crafty creatures, capable of mutating quickly and jumping from one animal species to the next. We've seen this happen routinely with birds and pigs, which have acted as reservoirs for H1N1 swine flu and bird flus that have eventually jumped to humans. Dogs, however, have long been considered to carry only one or two influenza A viruses that don't typically pose a threat to humans.1

This could be changing, though, if new research published in mBio is any indication2 — but don't give up cuddling with your favorite pooch during flu season just yet. Human flu outbreaks have been started when flu viruses jumped from birds into pigs, mutated and then jumped to people. The study suggests this type of leap could also occur with dogs acting as the intermediate host, but no such transmissions have occurred yet.

Could Sick Dogs Transmit Flu to Humans?

For the study, researchers sequenced the genomes of 16 influenza viruses obtained from dogs in Southern China. These were pet dogs with symptoms of respiratory illness who had been brought in for treatment at veterinary clinics, although the region is also known to have dogs raised for meat and free-roaming dogs in the streets, which, according to the American Society for Microbiology (ASM), creates a "more complex ecosystem for canine influenza virus transmission."3 Indeed, the analysis revealed the flu viruses contained segments from three lineages known to exist in Chinese pigs:

  • North American triple reassortant H3N2
  • Eurasian avian-like H1N1
  • Pandemic H1N1

The H3N2 viruses are known to circulate in Asian dogs, but it appeared they had reasserted with the H1N1 viruses that originated in pigs. This resulted in the creation of three new canine influenza viruses: H1N1r, H1N2r and H3N2r. Adolfo Garcia-Sastre, Ph.D., director of the Global Health and Emerging Pathogens Institute at the Icahn School of Medicine at Mount Sinai in New York City, explained:4

"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 reassorted with other viruses in dogs. We now have H1N1, H3N2, and H3N8 in dogs. They are starting to interact with each other. This is very reminiscent of what happened in swine ten years before the H1N1 pandemic."

What's more, because of the known ease with which flu viruses are known to jump from pigs to people, it's thought that canine influenza viruses that originate in pigs could pose a higher risk to humans than those that came from birds or other species, like horses.

Does Rescuing Dogs From China Raise the Risk of Flu Outbreak in the US?

Now that the existence of mutated flu viruses in Asian dogs that could potentially to jump humans has been confirmed, it's reasonable to consider how quickly such viruses could spread around the globe. Canine H3N2, once reserved for Asian dogs, has surged in the U.S., for instance. In the U.S., H3N8, which originated in horses and now also infects dogs, occurs largely in dog shelters.

In China, although the study used pet dogs, it's possible dogs raised "at higher densities for sale at live-animal markets, strays/street dogs, or both," could actually be the greater disease reservoirs. Further, in the Guangxi Zhuang Autonomous Region (Guangxi) where the study took place, international teams have increasingly taken to rescuing dogs from the controversial food trade, which could have repercussions on pandemic threats. According to the study:5

"Each June, Guangxi becomes a flashpoint for debate between dog owners and consumers during the annual Yulin Dog Meat Festival. International organizations have become increasingly active in rescuing Asian dogs destined for market. However, these activities increase the risk of spreading canine pathogens between continents …

The purchase of animals by international rescue organizations may also provide a secondary market for illicit activities involved in the theft of pet or street dogs for market.

China is a complex and diverse nation with a rapid and spatially uneven rate of modernization. It is important to understand how cultural changes in attitudes toward dogs could alter the frequency of contacts between dogs, live-animal markets, and humans across the country, and in turn impact CIV [canine influenza virus] dynamics and pandemic risk."

How to Keep Your Dog From Getting the Flu

Given their new findings, the researchers believe it's wise to consider ways to restrict the circulation of flu viruses among dogs. They suggested vaccination, but I recommend avoiding canine flu vaccines because they don't prevent infection. The vaccine may reduce viral shedding once infection is present, and may lessen the severity of symptoms and their duration, but it does not keep your dog from acquiring CIV.

Further, over-vaccination can seriously compromise your pet's immune system, leaving him more vulnerable to infections like the flu. It's important to understand that canine influenza is primarily associated with overcrowded conditions like those found in some shelters, kennels and dog racing facilities. Pet dogs are less likely to be exposed, unless they regularly spend time in close quarters with other potentially sick dogs, such as at doggy day care.

Further, even if your dog is exposed, he may show no symptoms at all and will likely recover quickly, assuming he's healthy. Top ways to prevent the flu in your dog include supporting his immune health by:

Worried About Catching the Flu From Your Dog?

If you're worried that your dog could make you sick, remember that no cases of humans being infected with canine flu have been reported. This doesn't mean it can't, or won't, happen, but using commonsense precautions, like washing your hands after cuddling with your pet, especially if he has been diagnosed with the flu, can't hurt. Also keep in mind that virus shedding peaks at three to four days post-infection, and the illness declines rapidly once your dog's immune system responds to the presence of the virus.

Keeping your own immune system strong by leading a healthy lifestyle is also important, but at this time you're far more likely to pick up a disease-carrying parasite from your pet than you are to pick up a flu virus. For now, perhaps it's not us humans that should be worried but the other way around: the first case of a human transmitting H1N1 flu to her cat occurred in 2009,6 and additional human-to-animal cases have been reported in cats and dogs since.