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New York City's mostly indoor cats easily caught SARS-CoV-2 during the first wave of the COVID-19 epidemic—and most were asymptomatic and were likely infected by their owners, according to a new study from a sample of cats that visited an Upper East Side veterinary clinic.

The study, in the International Journal of Infectious Diseases One Health, confirms that cats can efficiently catch SARS-CoV-2 from humans, though very few cases of humans catching it from cats have been reported.

Their results point to the importance of including pets in public health surveillance—as well as the low public health risk infected cats pose.

"The big concern at the time was that people would be putting their cats out onto the street, and overwhelming the shelters," said Gary Whittaker, the James Law Professor of Virology in the College of Veterinary Medicine (CVM) and the study's senior author. "It turned out that wasn't a concern. Cats do get exposed, but there's no reason to panic about that."

Humans are known to infect a wide range of animal species with SARS-CoV-2, including cats, dogs, mink and deer. Currently, very few studies have addressed the prevalence of SARS-CoV-2 in domestic cats during early stages of the pandemic, so this retrospective research addresses that gap. The study underscores the importance of a One Health approach to public health, which emphasizes the need to monitor diseases across people, animals and the environment to better understand and prevent pandemics, according to the paper.

In the study, blood samples were collected by clinicians from 79 domestic cats (33 male, 46 female) who visited the Sutton Animal Hospital for routine checkups. Samples were sent for testing to the Animal Health cDiagnostic Center (AHDC) at CVM. Bettina Wagner, a co-author of the paper and professor of population medicine and diagnostic sciences at CVM, and colleagues at the AHDC, who at the time were developing an advanced assay designed to detect human antibodies, which was then modified to measure antibodies that fight SARS-CoV-2 in cats.

During the study period, from June 2020 to May 2021, the samples revealed that 16% of the cats had antibodies to SARS-CoV-2, providing evidence of previous infection. Cats sampled in fall 2020 showed a 44% positive antibody rate, timing that coincided with a surge of human cases in New York City.

The animal practice was located near New York Presbyterian Hospital/Weill Cornell Medicine, where early COVID-19 patients were treated. While the cats' owners were anonymous, anecdotally, many of them lived nearby and worked at the hospital. Also, all but one of the cats had stayed at home, suggesting it was highly likely owners had exposed their cats to the virus. "The likely transmission route is from the hospital to the owner to the cat," Whittaker said.

The study found no link between a cat's age, breed or sex and likelihood of infection. Only two cats had signs of respiratory infection along with high levels of antibodies.

"There's information here for the future, in terms of the potential for the susceptibility of cats to this human virus and the fact that it spreads asymptomatically," Whittaker said.