Dogs carry a grab bag of flu viruses

Some dog flu viruses come from pigs, but there’s no sign yet that they can infect people

Some dogs in southern China carry flu viruses that came from pigs. The viruses probably spread most easily where animals are crowded, such as shelters, farms and markets.

AmyDreves/iStockphoto

Some dogs in China carry a mix of flu viruses, including viruses from pigs. The finding raises the possibility that dogs could pass the flu to people. This might set off a worldwide disease outbreak.

Just like people, some animals can get the flu. Different influenza viruses infect different kinds of animals, such as pigs and birds. Animals don’t all get the runny nose, fever and muscle aches that people do. Sometimes these viruses exist peacefully in the animals without making them sick. Other times, the infection can be deadly. Chickens and turkeys with the flu may have mild symptoms, such as ruffled feathers or a drop in egg laying. Some flu viruses may kill poultry by attacking the birds’ internal organs.

When animals get the flu, people’s biggest worry is that the rapidly changing viruses may jump from animals to humans. So scientists keep a close eye on these viruses. When people catch a new type of flu from animals or birds, it can be very bad. People’s immune systems may not be able to fight the new flu virus very well. If that happens, a person could get very sick and even die. And the new flu may spread around the world in what is called a pandemic.

Sneaky swine viruses

Dogs can get the flu, too. In the new study, researchers swabbed the noses of 800 dogs from 2013 to 2015. The dogs came from a part of southern China called the Guangxi region. All the dogs were sick with symptoms such as runny noses or coughs. And 116 of them were infected with flu viruses.

To the scientists’ surprise, some of the flu viruses in those dogs had originally come from pigs. (In the code that scientists use to describe different types of flu, these were H1N1 viruses.) The researchers studied the genes of 16 of the samples. They discovered that some of these swine flu viruses were types that had previously infected people and pigs in Europe and Asia. Others are types, or strains, that came from birds before infecting pigs — and then dogs.

In pigs, these viruses swapped genes among themselves to create new varieties. Some of these passed to dogs. The viruses aren’t exactly the same as the ones in pigs. The viruses have changed so that they can live in dogs and pass from pooch to pooch.

A virus similar to one of the swine viruses in dogs has already infected a person in China. That suggests that some swine flus can strike both pups and people.

This isn’t the first time researchers have discovered that dogs can get the flu. The first canine flu virus was described in 2005 in the United States. That was a horse flu virus called H3N8 that had jumped to dogs. It sometimes spreads among pooches in shelters. And, in 2010, scientists said some dogs in Asia carry a version of the H3N2 virus from birds. (Cats can catch the dog H3N2 flu virus. But they don’t usually pass it to other cats, as far as scientists know.)

Inside infected dogs in China, some of the viruses from the pigs mixed with bits of the H3N2 dog flu virus. This created the three new canine influenza virus strains, the researchers found. They report their results June 5 in mBio.

That genetic mixing could make the flu viruses more likely to infect lots of people and spread around the world, says study coauthor Adolfo García-Sastre. Those viruses might even be able to cause a pandemic. García-Sastre is a virologist who directs the Global Health and Emerging Pathogens Institute of the Icahn School of Medicine at Mount Sinai in New York City.

Since the study collected samples from only one part of China, the team doesn’t know how common it is for dogs to carry flu. They also don’t know how many different dog influenza viruses may be out there.

Beware wet noses?

Flu viruses in dogs have evolved very quickly, over just a few years, García-Sastre says. There’s no sign yet that the dog flu viruses can infect people. But that could change. The more types of viruses are in an animal, the higher the chances are that one will be able to jump to humans, he says.

Pigs and birds are still the most likely animals to mix up the next human pandemic influenza virus, says Amesh Adalja. He’s an infectious disease doctor at Johns Hopkins University in Baltimore, Md., and a spokesperson for the Infectious Diseases Society of America.

Even if a dog flu virus infected a person, the virus might not be able to pass easily between people. That’s an important characteristic a virus must have before it can spread around the world.

But most people touch a wet dog nose far more often than a pig nose. So it’s worth keeping an eye on the pups, Adalja says. “Knowing that dogs could contribute is important for preparing for the next pandemic, because we don’t know exactly what that virus will be,” he says.

García-Sastre agrees that finding flu viruses in dogs isn’t cause for alarm. But researchers should monitor the situation, he says. Using vaccines and keeping sick dogs away from others, may keep the canine viruses from catching hold in humans.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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