When it comes to studies about pets and COVID, it’s always something.

It turns out the relatively small number of cats and dogs who have tested positive in the US for SARS-CoV-2 (fewer than 50, according to a list maintained by the United States Department of Agriculture Animal and Plant Health Inspection Service) may not reflect the number of actual cases of pets who have SARS-CoV-2. Preliminary findings from a new study from the University of Guelph’s (UG) Ontario Veterinary College suggest that a “substantial proportion” of pets can catch the virus from infected people.

The researchers presented the study, which is yet to be peer reviewed or published, as an abstract at the European Society of Clinical Microbiology and Infectious Diseases Conference on Coronavirus Disease last week.

Their findings suggest that the reason for the potential undercount is the type of test predominantly used to detect SARS-CoV-2 in both animals and humans: a technique called polymerase chain reaction (PCR) that can miss cases that other tests will pick up, depending on when the infection was active.

Lead researcher Dorothee Bienzle, DVM, PhD, professor of veterinary pathology at UG, explained their findings to NEWStat.

“The virus SARS-CoV-2 is detected by a quantitative PCR assay in nasopharyngeal swabs in both humans and pets,” she said. “Antibodies to the virus develop two to four weeks after infection in the blood, and as far as is known, they last for at least six months.”

In this study, Bienzle and her colleagues collected swabs from 17 cats, 18 dogs, and 1 ferret from households where a human had tested positive for COVID-19. All PCR results were negative for current infection except those of 1 cat, whose results were considered inconclusive.

Blood samples were then taken from a subset of 8 cats and 10 dogs, and standard blood antibody enzyme-linked immunoassay tests were performed to detect recent or past infection.

The blood tests told a very different tale from the PCR tests.

Results of the blood tests indicated the presence of antibodies in seven of the cats, including the cat whose PCR test was indeterminate, indicating present or past infection, depending on the type of antibody. Two of the dogs tested positive for the antibodies that indicated past infection. One of whom was reported to have had an episode of respiratory disease, though it’s unknown if the episode was caused by the virus.

“Our study revealed that more than 50% of a small and targeted sample of [pets] living with persons who had COVID-19 were antibody positive,” Bienzle summarized. “That means they had been infected with SARS-CoV-2.” She said the infected cats and dogs most likely acquired the infection from the COVID-positive people. Furthermore, several of the infected pets had COVID-19-like respiratory symptoms at the same time their owner had COVID-19. “[This indicates] that cats are infectable by SARS-CoV-2 and that some experience transient disease.”

Bienzle said dogs appear to be less prone to SARS-CoV-2 infection than cats, and generally don’t appear to show COVID-19 symptoms. The one thing we do know for certain, she said, is that “persons who have COVID-19 can infect pets.”

Bienzle added that, as far we know, no pets have caught COVID-19. In other words, while a few have tested positive for the virus and even fewer have exhibited mild symptoms, none have actually been diagnosed with the disease.

In short, Bienzle said, “We should consider that people with COVID-19 are infectious to pets, not just to other people. Therefore, a cat who becomes infected in a household could spread infection.” As a result, she said, in keeping with public health recommendations, “Pets should be isolated from infected persons if possible.” And infected pets should be kept away from both other pets and people.

Because sadly, according to Bienzle, there’s one potential finding that remains frustratingly, maddeningly, elusive: “We cannot be certain that infected pets do not transmit the virus on to other pets, or back to people.”

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