Dogs carry a grab bag of flu viruses | Science News for Students

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
Jul 19, 2018 — 6:45 am EST
a photo of a dog with a sad expression

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.


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.

Power Words

(more about Power Words)

birds     Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.

canine     Members of the biological family of canids. These are carnivores and omnivores. The family includes dogs, wolves, foxes, jackals and coyotes. 

coauthor     One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.

egg     The unfertilized reproductive cell made by females.

flu     (see influenza)

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

H1N1     A type of influenza virus that infects mainly swine. A few of the strains have developed the ability to spread in people as well.

immune     (adj.) Having to do with the immunity. (v.) Able to ward off a particular infection. Alternatively, this term can be used to mean an organism shows no impacts from exposure to a particular poison or process. More generally, the term may signal that something cannot be hurt by a particular drug, disease or chemical.

immune system     The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

infect     To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.

infection     A disease that can spread from one organism to another. It’s usually caused by some type of germ.

infectious     An adjective that describes a type of germ that can be transmitted to people, animals or other living things.

influenza     (also known as flu) A highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.

monitor     To test, sample or watch something, especially on a regular or ongoing basis.

muscle     A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

outbreak     The sudden emergence of disease in a population of people or animals. The term may also be applied to the sudden emergence of devastating natural phenomena, such as earthquakes or tornadoes.

pandemic     An epidemic that affects a large proportion of the population across a country or the world.

pathogen     An organism that causes disease.

poultry     Chickens, ducks, geese, pheasants and turkeys that are raised by people. In the wild, these same birds are referred to as fowl.

pup     A term given to the young of many animals, from dogs and mice to seals.

society     An integrated group of people or animals that generally cooperate and support one another for the greater good of them all.

strain     (in biology) Organisms that belong to the same species that share some small but definable characteristics. For example, biologists breed certain strains of mice that may have a particular susceptibility to disease. Certain bacteria or viruses may develop one or more mutations that turn them into a strain that is immune to the ordinarily lethal effect of one or more drugs.

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

vaccine     (v. vaccinate) A biological mixture that resembles a disease-causing agent. It is given to help the body create immunity to a particular disease. The injections used to administer most vaccines are known as vaccinations.

virologist     A researcher who studies viruses and the diseases they cause.

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.


Journal: Y. Chen et al. Emergence and evolution of novel reassortant influenza A viruses in canines in Southern China. mBio. Vol. 9, June 5, 2018. doi:10.1128/mBio.00909-18.