Cats can be infected with the coronavirus that causes COVID-19 and spread it to other cats, but dogs are not really susceptible to the infection, according to researchers in China. The team, at Harbin Veterinary Research Institute in China, also concludes that chickens, pigs, and ducks are not likely to catch the virus.

Scientists say the findings are interesting, but that cat-owners should not be alarmed just yet. The results are based on lab experiments in which a small number of animals were deliberately infected with high doses of the virus, SARS-CoV-2, and do not represent real-life interactions between people and their pets, says virologist Linda Saif at The Ohio State University in Columbus. There is no direct evidence that the infected cats secreted enough coronavirus to infect people, she says.

Pet patrol

With the coronavirus spreading rapidly around the world, some have raised concerns about whether the virus can pass between pets and people. So far, there have been a few reports of pets being infected: a cat in Belgium and two dogs in Hong Kong. “Cats and dogs are in close contact with humans, and therefore it is important to understand their susceptibility to SARS-CoV-2 for COVID-19 control,” write the authors of the latest study, a preprint posted on bioRxiv on 31 March.

The team, led by virologist Bu Zhigao, infected five domestic cats with SARS-CoV-2 through the nose. When two of the cats were euthanized six days later, the researchers found viral RNA, as well as infectious virus particles, in their upper respiratory tracts.

The other three infected cats were put in cages next to three uninfected felines. The team later detected viral RNA in one of the non-infected cats, which suggests that they contracted the virus from the infected cats through respiratory droplets. All four cats also produced antibodies against SARS-CoV-2. Surveillance for SARS-CoV-2 in cats should be considered as part of efforts to eliminate COVID-19 in humans, the authors note in the preprint, which has not been peer reviewed.

No symptoms

But Saif says that none of the infected cats showed symptoms of illness, and that only one out of the three felines exposed to infected animals caught the virus. “This suggests the virus may not be highly transmissible in cats,” she says. Furthermore, the mode of transmission is unclear because the study does not describe how how the cages were set up, and the uninfected cats could have contracted the virus from contaminated faeces or urine.

More tests are needed where cats are infected with different doses of the virus to see, for example, whether they can pass it on to other cats, she says.

The results suggest that cats should be considered an element in the effort to control COVID-19, but that they’re not a major factor in the spread of the disease, says Dirk Pfeiffer, an epidemiologist at the City University of Hong Kong. “The focus in the control of COVID-19 therefore undoubtedly needs to remain firmly on reducing the risk of human-to-human transmission.”

Previous studies of the virus that caused severe acute respiratory syndrome, SARS, have shown that cats can be infected with SARS-CoV and pass it on to other cats. But “there was no indication that during the SARS pandemic that SARS-CoV became widespread in house cats or was transmitted from cats to humans”, says Saif.

The United States Centers for Disease Control and Prevention recommends that people infected with COVID-19 limit contact with their pets, including avoiding petting, being licked and sharing food and utensils.

“These are precautionary as would be advised for any new emerging disease where only limited information is available,” says Saif.

Other animals

The researchers also found that ferrets are also highly susceptible to coronavirus SARS-CoV-2 infection, which they suggest makes them a suitable model for testing potential vaccines and drugs. Several labs have already started COVID-19 research on them.

Dogs, however, were less susceptible to the virus. The researchers infected five young dogs and found that two excreted viral RNA in faeces, but none contained infectious virus.

Similar investigations in pigs, chickens and ducks identified no viral RNA in animals deliberately infected with the virus, or those exposed to the infected animals.

These findings suggest that none of these species plays a role in the epidemiology of COVID-19 infection, says Pfeiffer.

This article is reproduced with permission and was first published on April 1 2020.

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