A team of researchers studied the transmission of the coronavirus between cats and found that felines are capable of infecting each other with the virus. There have not been any known cases of a cat spreading COVID-19 to a person, but the scientists say it's possible felines could be "a silent intermediate host" for the virus, and they believe more research is needed.
"This is of particular importance given the potential for SARS-CoV-2 transmission between family members in households with cats while living under 'shelter-in-place' orders," they write in a letter published in the New England Journal of Medicine on Wednesday.
The research team, lead by Yoshihiro Kawaoka, professor of pathobiological sciences at the University of Wisconsin School of Veterinary Medicine, inoculated three cats with the virus, and then introduced three other uninfected cats to the group. In five days, the three previously uninfected cats had caught the virus.
They note that none of the cats ever showed any signs of illness.
The researchers say recent reports of COVID-19 transmissionand between , coupled with their recent data, shows "there is a public health need to recognize and further investigate the potential chain of human–cat–human transmission." Previous studies have shown that cats and ferrets are susceptible to the virus, but .
Both Kawaoka and Peter Halfmann, a research professor at University of Wisconsin–Madison who helped lead the study, advise people withto avoid contact with cats. They also say cat owners should keep their pets indoors to limit the interaction their cats have with other animals and people.
"It's something for people to keep in mind," Halfmann said. "If they are quarantined in their house and are worried about passing COVID-19 to children and spouses, they should also worry about giving it to their animals."
While the cats in the study did not show any symptoms, a tiger at the Bronx Zoo tested positive for the virus last month after developing a dry cough and decrease in appetite. Zoo officials believe the tiger was likely infected by a human caretaker. Three other tigers and three African lions also developed symptoms and all were expected to recover, the zoo said.
According to the CDC, there is still much to learn about this virus, "but we know it is primarily spreading from person-to-person and it appears that it can spread from people to animals in some situations." The CDC has issued guidelines for pet owners regarding COVID-9.
While the CDC says there is "there is no evidence that animals play a significant role in spreading the virus that causes COVID-19," there have been instances where other viruses spread that way. In 2016, an H7N2 influenza outbreak in cats at a New York City animal shelter infected a veterinarian, a case that "highlighted the public health implications of cat-to-human transmission to workers in animal shelters," according to the authors of the new study.
The researchers say that, given the need to stop the coronavirus pandemic, studying the role cats may play in the transmission of the disease to humans is needed.
Dr. Ann Hohenhaus, an internal medicine and small animal veterinarian at New York City's Animal Medical Center, spoke to CBS News about what the study means for pet owners.
"Is there a hard-and-fast study that says cats can absolutely not spread this to humans? No," said Hohenhaus, who was not part of the study. "But we also have no evidence of the converse, which is that cats are spreading it to people. This study doesn't change that."
Hohenhaus said there are millions of people worldwide infected with COVID-19 but only a "smattering of reports of cats." She also explained how cats could potentially catch the virus from humans but might not be able to transmit it back to them.
"How a virus works is that the virus gets to your body, and then your cells have to have a receptor that the virus plugs into, and then that receptor drags the virus into the cells," Hohenhaus said. "So, it's kind of like an outlet and a plug on a cord: If you've got a three-prong cord and a two-prong outlet, then the virus won't get in. So, cats clearly have a receptor that matches the virus."
Hohenhaus also said cats might not replicate the virus in their cells as well as humans do. She explained that when people have a "high viral load" in their bodies, they appear to get sicker with COVID-19 than people with lower viral levels. "So, since cats don't seem to get very sick, maybe they don't have a very high virus level. And therefore, they don't make enough virus in their cells that when they sneeze it back out their nose there's not enough virus to make people sick."
It's not unheard of for an animal to transmit a virus to humans, Hohenhaus said. However, she wants to remind pet owners that "this new article highlights what veterinarians think, and that is: more research is necessary."
"It does not change our recommendation that if you are sick, social distance your pets, quarantine yourself away from everyone in the family — that includes the pets," she continued. "And if you've got COVID-19 and your pet is acting sick, please call your veterinarian and talk about what's going on so a safe plan for everyone can be made for your pet."