Last week, I called out Maddie’s Fund and some of its partner organizations for fearmongering about whether people can get infected with SARS-COV-2 from dogs and cats, because the evidence clearly says they cannot.
News reports, however, have suggested that a new study conducted by government officials in China concludes the opposite for cats (though not dogs) — that they can get it from humans and then give it to one another. The headlines proclaim that “cats can get coronavirus.” But such headlines may obscure more than they illuminate and a closer reading of the study does not support the emphatic claims.
What did the study actually do? And what were the results?
In analyzing the study, I will focus on the methodology used and subsequent criticisms by epidemiological experts. What this article won’t dwell on — though it should go without saying — are the ethical issues inherent in any study that would deliberately attempt to inflict on sentient, non-human animals a disease so grave in terms of potential suffering and death that we have all collectively adopted extreme measures, including shutting down the economies of the world, to avoid contracting it ourselves.
What did the researchers do?
The study was designed to determine whether certain animals — cats, dogs, ferrets, chickens, pigs, and ducks — could contract COVID-19 and whether they could pass it on to others of their species. It was not looking to determine whether these animals could pass it along to people as the evidence from a broad range of sources — including the World Health Organization, the Centers for Disease Control, the U.S. Department of Agriculture, and the American Veterinary Medical Association — have largely ruled that out.
Researchers took six pairs of cats (and similar pairs of the other animals), and injected them, intranasally, with large amounts of particles of SARS-CoV-2, the virus that causes COVID-19, to see if they developed COVID-19. They were then placed next to other cats in cages to see if others of their species contracted it from them.
After a few days, the animals were killed and dissected. Based on the presence of lesions, antibodies, and other factors, the study authors determined which animals developed COVID-19 and which did not. None of the cats displayed outward symptoms of the disease.
What does the study show?
In a laboratory setting, when massive amounts of the virus was introduced directly into their nasal cavities, cats (and ferrets) were susceptible to COVID-19 and capable of transmitting it to other cats (and ferret-to-ferret). Dogs and the other other animals tested were determined not to be susceptible to COVID-19.
What does the study not show?
The study does not show that cats or other animals, infected or not, can transmit COVID-19 to humans. As stated, other research likely rules this out already. This study does not show that infection or transmission in non-laboratory conditions is probable.
What are the limitations of the study?
A typical human cough can spray roughly 3,000 large particles. A sneeze, by contrast, can result in upwards of 40,000. A human who is in the near presence of a sneezing human will inhale only a fraction of that. But the study in question injected the cats with 100,000 particles from a human patient directly up their noses, a massive dose and several orders of magnitude of what would be found in a community impacted by COVID-19.
And while the cats did have antibodies and lesions, none of the cats had outward symptoms. In addition, only one highly-stressed, caged “aggressive” cat who could not escape the other cat (or his captors) was determined to be infected by an injected cat, and again, the cat had to be killed in order to determine if lesions or antibodies were present because outward signs were not obvious; the cat did not appear to be ill.
In short, the study was done in extreme conditions, where the (feral and caged) cats were stressed and exposed to massive quantities of the virus that causes COVID-19. And (thankfully for the sake of the cats) the sample sizes were so low we have no information about what the transmission rate may be.
What do the experts say?
A professor of microbiology at the University of Pennsylvania’s School of Veterinary Medicine called for caution, saying: “All this study showed is that they could experimentally infect cats: It doesn’t mean that the virus is causing disease in the cat population, and it does not mean that cats can infect humans”. She also noted that the study does not prove contagion and transmission will naturally occur outside a laboratory environment.
The head of the Zoological Pathology Program at the University of Illinois veterinary school says, “Given the number of people in this country that have been infected with the virus and have become ill, and the number of people in this country that own domestic cats, it seems fairly improbable that cats are an important source of the virus:” (In distinguishing pet cats from the tiger at the Bronx New York Zoo which tested positive for the virus, she notes that tigers are of a different genus than pet cats and, once again, the tiger was in a confined, stressful, institutional setting.)
Likewise, the American Veterinary Medical Association, in a statement echoed by both the Centers for Disease Control and the U.S. Department of Agriculture, says, “that dogs and cats are not readily infected with SARS-CoV-2, we have little to no evidence that they become ill, and no evidence that those that may be naturally infected spread SARS-CoV-2 to other pets or people”.
What should we do?
Nothing in the study shows that we should fear cats, round up community cats, require surveillance of cats, quarantine cats, or stay away from our cats. Once again, the UPenn professor is instructive: “We can still play with our cats at home, snuggle with them, and pet them:” If we do one thing different, the professor suggests that “we wash our hands afterward.”
The study, Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS-coronavirus 2, is here.
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