Study shows case of probable cat-to-human virus spread, but risk remains low


Study shows case of probable cat-to-human virus spread, but risk remains low

A veterinarian in Thailand likely contracted the coronavirus from an infected domestic cat last year, researchers conclude in a new study. It is the first documented case of suspected cat-to-human transmission, although experts stress that the overall risk of cats infecting humans with the virus remains low.

One of the cat’s two owners, who both had Covid-19, likely passed the virus on to the cat, which then sneezed in the vet’s face, according to the paper, authored by scientists from Thailand’s Prince of Songkla University. Genome sequencing confirmed that the cat and all three individuals were infected with an identical version of the virus, which was not widespread among the local population at the time.

Cats are much more likely to catch the virus from people than transmit it to them, scientists say. But the case is a reminder that people infected with the virus should take precautions around their pets – and that veterinarians and shelter workers who may come into contact with infected animals should do the same, said Dr. Scott Weese, an infectious disease veterinarian at the University of Guelph in Ontario.

“Too often when things become human diseases, we forget about everything else,” he said. “I think it’s important that we recognize that this virus can still move between species.”

Previous research has shown that pet owners can infect their cats and that, under certain conditions, cats can transmit the virus to each other. However, it has been difficult to prove that cat-to-human transmission occurs in natural settings. (Mink, hamsters, and deer have been reported to transmit the virus to humans.)

The new paper appeared this week in the journal Emerging Infectious Diseases, published by the US Centers for Disease Control and Prevention. It’s a strong argument for cat-to-human transmission, said Dr. Weese: “You have a pretty good story here.”

On August 4, a father and son in Bangkok developed symptoms of Covid-19 and subsequently tested positive for the virus. Due to a shortage of hospital beds in Bangkok, the two men were taken in a 20-hour ambulance ride on August 8 to a hospital in Songkhla, a province in southern Thailand. For unclear reasons, they brought their house cat with them.

When the men were hospitalized, the cat was sent to a veterinary clinic for examination. Although the cat appeared healthy, the vet, a 32-year-old woman, took nasal and rectal swabs that tested positive for the virus. As the vet wiped the cat’s nose, the animal sneezed in her face. (The vet wore gloves and a mask during the exam, but no face shield or eye protection.)

On August 13, the vet developed Covid-19 symptoms, including a fever and cough. Shortly after, she tested positive for the virus.

Genome sequencing revealed that the cat’s owners, cat and veterinarian were all infected with the same version of the delta variant, which differed from virus samples collected from other patients in Songkhla at the time.

PCR tests indicate the cat had a high viral load at the time of her vet exam. It is known that none of the vet’s close contacts had Covid-19 at the time and she had no previous encounters with the pet’s owners, supporting the theory that the cat was the source of the vet’s infection. (It wasn’t clear if she later met with the owners.)

The CDC recommends people infected with the virus avoid contact with their pets. “If you’re trying to stay away from people because you might be contagious,” said Dr. Weese, “just try to stay away from animals at the same time.”

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