With sporadic reports in recent weeks of cats infected with the coronavirus that causes Covid-19, a group of researchers set out to determine whether cats can transmit the pathogen to one another.
The answer, the scientists said: They can. The question now is whether felines can transmit SARS-CoV-2 back to people.
Researchers from the University of Wisconsin-Madison and the University of Tokyo noted that none of the cats in their study was visibly ailing, but they shed the virus from their nasal passages for about six days.
“Considering the amount of virus we found coming out of the noses of the cats … there is the possibility that these cats are shedding, fomites are being released in a person’s household or at cat shelters or human societies and that somehow people could possibly pick up the virus. I think it’s something people should be aware of,” said Peter Halfmann, a research professor at the University of Wisconsin and first author of the study, published as a letter in the New England Journal of Medicine.
“It depends on the household and the cat, but there could be a lot of close contact with your pet cat on occasion,” Halfmann said.
The researchers, led by virologist Yoshihiro Kawaoka, experimentally infected three cats, and then placed an uninfected cat into each of the cages housing the infected animals a day later. The three uninfected cats were all infected within five days.
Halfmann said uninfected cats were also put into cages a foot away from the cages containing the infected cats. None of those felines became infected with the virus.
In early April, Chinese researchers reported that cats and ferrets were susceptible to infection. A few weeks later the U.S. Department of Agriculture announced that two pet cats in New York state had tested positive for the virus. At least eight big cats at the Bronx Zoo — tigers and lions — were also infected with the virus.
Many research groups have reported on virus shedding with Covid-19 by simply conducting testing by polymerase chain reaction, or PCR. A positive PCR hit tells you that the human or animal is shedding something, but it doesn’t reveal if they are emitting viral debris — which poses no risk of infection — or actual infectious viruses.
The researchers responsible for this work did attempt to grow viruses from swabs taken from the noses and rectums of the cats; they found that all the animals were emitting infectious viruses from their noses. None of the rectal swabs produced infectious virus.
Halfmann said there was quite a lot of virus — between 30,000 and 50,000 virus particles per swab. But what that means isn’t clear, he said. It’s not known how big a dose of virus is needed to infect a person. And there’s no ethically acceptable way to construct a trial to see if cats can infect people.
Still the researchers suggested people should be aware of the possibility of transmission from cats to people, and keep cats away from anyone in a household who is suspected of being sick with Covid-19. “I think it’s good practice to have this in people’s minds,” Halfmann said. He and his co-authors also urged people not to abandon cats or give them up for adoption because of such concerns.
They also advised cat owners to keep their cats indoors.
“Cats are still much more likely to get Covid-19 from you, rather than you get it from a cat,” Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, said in a statement.