Cats appear to be more susceptible to Covid-19 infection than dogs, and kittens may be more susceptible than older cats, say researchers investigating infection and transmission in domesticated animals. Other scientists say there is still no conclusive evidence to suggest the virus can be passed from pets to humans, but people should keep their animals indoors as much as possible to reduce the possibility of exposing them to infection. In a new study, Chinese researchers have found that though cats may be “highly susceptible” to the virus and can transmit it to other cats, they are not a major factor in spreading the disease. It has previously been reported that cats could be infected after pets in both Belgium and Hong Kong tested positive. In a series of laboratory experiments by the research team from the Chinese Academy of Agricultural Sciences’ Harbin Veterinary Research Institute in northeast China, cats inoculated with the virus developed obvious infections. The team’s non peer-reviewed article was published on Biorxiv.org on Tuesday. They found that cats that did not receive the inoculation but were kept near the infected cats also became infected. “The researchers in Harbin used two strains of viruses, one from the environment sample collected from Huanan Seafood Market in Wuhan, which was linked to the initial outbreak, and one from a human patient from Wuhan. These were then used to infect six cats, while 12 others were used for a transmission test. Of the six, lesions were found in two juveniles.” The experiments were conducted in the institute’s biosafety level 4 animal laboratory, China’s only veterinary laboratory at this high level. The human virus was inoculated via the nose into the subadult feline subjects. In three to five days, the viral RNA was detected in their faeces, and after the cats died or were euthanised, the infectious virus was also widely detected in their organs, including nasal turbinates, soft palates, tonsils, and trachea. RNA – or ribonucleic acid – is a molecule that carries genetic codes in some viruses. After experiments were conducted on two younger cats, aged 70-100 days and designated as “juvenile cats”, massive lesions were found in the nasal and tracheal mucosa epitheliums, as well as the lungs. “These results indicate that SARS-CoV-2 can replicate efficiently in cats, with younger cats being more permissive,” the researchers said. In the transmissibility experiments, cats that were placed in separate cages next to the virus-inoculated cats were also found infected later, which suggested the cat-to-cat transmission took place not through direct contact, but possibly via respiratory droplets – in the same way the disease transmits between humans, according to the researchers. In similar experiments, dogs showed low susceptibility. Although inoculated beagles tested positive to the viral RNA in their rectal swabs, no infectious virus was found. No trace of the virus was detected in their organs after euthanasia. Researchers also carried out virus inoculation and transmissibility experiments on ferrets and other common animals. Livestock that have close contact with humans, including pigs, chickens and ducks, were found not susceptible to the virus, while ferrets, an animal frequently used for the study of human respiratory viruses, were found “highly susceptible”, much like the cats. A separate evaluation by US-based Idexx Laboratories showed no positive results in either cats or dogs from 3,500 cat and dog specimens in South Korea and all 50 US states, suggesting that Covid-19 is primarily transmitted person-to-person. The research follows reports that a cat in Belgium developed breathing difficulties and tested positive to coronavirus and that a cat living with an infected woman in Hong Kong tested positive but showed no signs of the disease. The two cases triggered concerns over whether pets were a key factor in spreading the disease, but there is no evidence that cats can spread the deadly virus to humans. Hong Kong has reported two dogs testing positive but neither had apparent symptoms, suggesting limited reproduction of the virus in these pets. Other scientists said the research findings were valid, but that the results did not suggest cat owners should be alarmed. Edgar Wayne Johnson, a veterinarian and senior technical consultant at Enable Ag-Tech Consulting in Beijing, said it was important not to overreact to the findings as the cats had been exposed to a large dose of the virus. “It is an interesting study, but I suggest calmness in the face of this report,” he said. “Since I don’t hear of any reports of feline illness in households with SARS2, I am not ready to suggest to people that they take their cats to the vet for examination or anything.” He said cat owners were advised to keep their pets inside so as to reduce the chances of exposure to an infected animal. “At this point I would advise benign neglect. Take care of your pets much the same as you would any other day. If you pet is ill, seek professional assistance,” he said. The most important message of the research was that dogs are quite unlikely to spread the disease, he said. “There had indeed been a great deal of concern about dogs and this virus.” Muhammad Munir, a virologist at Lancaster University in northern England, said it was too early to say if Covid-19 was spreading among animals, but it was advisable for animals to be tested to see if they were capable of causing infection or carried the virus on their bodies. The question was whether the virus could be transmitted between animals and humans, and if animals showed any clinical signs if infected, he said. “This is a new disease and it’s only three and a half months old, so we need to be keeping an eye open to all of the possibilities,” he said. “On the safe side, it would be best to be testing animals, the same way as we do for humans … that would be advisable in the situation, when we are not 100 per cent clear cut about the circulation of Covid-19 in animals, and until we know, it is advisable to screen those animals, especially cats, based on this study.” Munir advised pet owners to have their cats and dogs tested for Covid-19, and to quarantine them if they tested positive. Linda Saif, a virologist at the Ohio State University in Wooster, was quoted by Nature as saying that there was no direct evidence that infected cats would spread the coronavirus to humans. The research findings were based on lab experiments and deliberate use of high doses of the virus, which did not suggest genuine interactions between human and pets, she said. Additional reporting by Sarah Zheng Sign up now and get a 10% discount (original price US$400) off the China AI Report 2020 by SCMP Research. Learn about the AI ambitions of Alibaba, Baidu & JD.com through our in-depth case studies, and explore new applications of AI across industries. The report also includes exclusive access to webinars to interact with C-level executives from leading China AI companies (via live Q&A sessions). Offer valid until 31 May 2020.