Science’s COVID-19 reporting is supported by the Pulitzer Center and the Heising-Simons Foundation.
Last month, the first U.S. dog to definitively test positive for COVID-19 died in New York City. The canine—a German shepherd named Buddy—likely had lymphoma, but the case served as a reminder that pets, too, are at risk.
Now, COVID-19 cases are surging in some areas of the United States, including in places that had largely escaped the virus in the spring, and some countries around the world are grappling with renewed outbreaks. People are also wondering and worrying about their pets.
Scientists are, too. It remains unclear, for example, how often cats and dogs become infected with the virus, what their symptoms are, and how likely they are to pass it along to other animals, including us. Yet veterinarians are hard on the case, and a handful of studies are starting to provide some answers. Experts have some concrete advice based on what we know so far.
We’re a much bigger risk to our pets than they are to us.
Federal health agencies and veterinary experts have said since the beginning of the pandemic that pets are unlikely to pose a significant risk to people. Hard evidence from controlled studies for this assertion was lacking—and still is—but everything scientists have seen so far suggests cats and dogs are highly unlikely to pass SARS-CoV-2 to humans. “There’s a lot greater risk of going to the grocery store than hanging out with your own animal,” says Scott Weese, a veterinarian at the University of Guelph’s Ontario Veterinary College who specializes in emerging infectious diseases and who has dissected nearly every study on COVID-19 and pets on his blog.
Indeed, pets are much more likely to get the virus from humans than the other way around. “Almost all pets that have tested positive have been in contact with infected humans,” says Jane Sykes, chief veterinary medical officer at the University of California, Davis, and a founder of the International Society for Companion Animal Infectious Diseases, which is providing COVID-19 information to both pet owners and veterinarians. A genetic study of the viral sequences in the first two dogs known to have COVID-19 indicates they caught it from their owners. Even tigers and lions infected at New York City’s Bronx Zoo in April appear to have contracted the virus from humans.
But some researchers caution that this finding may be due in part to limited testing: Most of the pets that have been evaluated got the tests because they lived with humans who had already tested positive. “It’s a stacked deck,” says Shelley Rankin, a microbiologist at the University of Pennsylvania School of Veterinary Medicine, whose lab is part of the U.S. Food and Drug Administration’s Veterinary Laboratory Investigation and Response Network.
Still, most researchers think pets pose little risk to people—and to other pets as well. A few studies have shown that cats can transmit SARS-CoV-2 to other cats, but all were conducted in an artificial laboratory setting. And, like many COVID-19 studies in humans, most studies are preprints that have yet to be published in peer-reviewed journals. What’s more, Sykes notes there have been multiple reports of households where one pet tested positive and others didn’t. “Everything we’ve learned so far suggests that it’s unlikely that pets are a significant source of transmission,” she says.
COVID-19 symptoms in pets are likely mild to nonexistent.
Because pet testing remains rare, it’s unclear how many cats and dogs have been infected with SARS-CoV-2. A serological preprint published last month indicated that 3% to 4% of cats and dogs in Italy had been exposed to the virus at the height of the pandemic there—comparable to the rate among people.
But even if the numbers are really that high, there hasn’t been a concomitant uptick in symptoms. The Seattle-based Trupanion, which provides health insurance for more than half a million dogs and cats in North America and Australia, says it has not seen an increase in respiratory claims—or any other type of health claim—since the pandemic began. “No big trends are jumping out,” says Mary Rothlisberger, the company’s vice president of analytics, even when she looked at pandemic hot spots. Two recent studies have also shown that cats, at least, are unlikely to exhibit symptoms. “My gut sense is that [the disease is] much more minor than we’re seeing in people,” Sykes says.
That could mean pets are silent transmitters of the virus, as some scientists have suggested, but so far there’s no direct evidence for this.
It probably doesn’t make sense to get your pet tested.
Several pet tests are available, but they aren’t widely used because the priority has been on human testing. Agencies like the United States Department of Agriculture have cautioned against routine testing of cats and dogs.
Even if your pet does test positive, Weese says, “What are you going to do with the results?” If your dog or cat has COVID-19, it’s probably because you do too, he says. “It doesn’t change anything for the pet or the family.” And because there aren’t any drugs for the disease, he says, “We wouldn’t prescribe anything” for the pet.
Safety precautions for pets haven’t changed.
Whether it comes to taking your dog to a dog park or petting an outdoor cat, the standard advice still holds: Wear a mask, wash your hands, and social distance. “If you are not taking precautions … you are putting both yourself and your animal at risk,” Rankin says. But, she says, “If you are a responsible pet owner, then it is probably safe to say that your animal’s risk [of infection] is lower than yours.”
Weese agrees that people should be more concerned about other humans than about pets. “The risk from people present at dog parks or vet clinics is much higher than the risk from dogs at those locations,” he says.
Scientists still have more questions than answers.
Researchers are just beginning to understand how companion animals play into the pandemic. The pet studies so far “are all part of a puzzle we’re still trying to put together,” Sykes says.
And they’re preliminary. “Almost every preprint I have seen is flawed in some way,” says Rankin, who dings small sample sizes, incomplete data, and a lack of vigorous testing. That doesn’t necessarily invalidate the results, but she and others would like to see more robust studies.
Sykes and Weese, for example, want more research done in the home. That could give scientists a better sense of how likely pets are to transmit the virus to other pets, how long pets remain contagious, and what—if any—clinical signs of COVID-19 show up.
Rankin is part of a project to do what she calls “full-on epidemiology” of the complete medical backgrounds, including any COVID-19 cases, of 2000 pets that have been seen at her vet school for various reasons, or just for routine checkups. The hope is that such an approach will weed out some of the biases of previous studies—such as those that only looked at pets in COVID-19–positive homes—and get a better sense of the true risk factors for the disease.
Sykes and Weese are involved in similar endeavors. Weese also hopes to investigate whether pets, especially feral and outdoor cats, pose a risk to wildlife. “If we want to eradicate this virus,” he says, “we need to know everywhere it might be.”
Other researchers are exploring whether drugs that treat other coronaviruses in cats could also combat COVID-19 in both pets and people. “Answering these questions isn’t just important for companion animal health,” Sykes says. “It could help us, too.”