first confirmed case of cat-to-human transmission

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In April 2022, hundreds of white-tailed deer tested positive for SARS-CoV-2. Scientists are therefore increasing research on animals that could serve as a natural reservoir for the virus in order to understand the mechanism of propagation on the one hand within the species, and on the other hand through different taxa. The aim is to prevent any zoonosis, that is to say the transmission of the virus from animals to humans. Recently, Thai scientists report the first solid evidence of a pet cat infecting a person with SARS-CoV-2, adding felines to the list of animals that can transmit the virus to humans.

In March 2021, nearly a year into the pandemic, a seemingly healthy wild mink tested positive for SARS-CoV-2 in Utah. No reports of the virus being contracted by an animal in the wild had previously occurred, although researchers have been monitoring this closely.

Since the virus began spreading around the world, scientists feared it could jump from humans to wild animals, meaning it could hide among various animal populations, and eventually mutate and then reappear in humans even after the pandemic is over.

Wild animals are not the only ones to have attracted attention. Studies have shown that SARS-CoV-2 can infect many domesticated and captive animals, from cats and dogs, cougars, gorillas and snow leopards in zoos, to farmed mink. Outbreaks in mink farms have already shown that infected animals can transmit the virus to humans. Recently, researchers reported the first confirmed case of transmission of the virus from a tabby cat to a human. The article is published in the journal Emerging Infectious Diseases.

Cats: suspects since the start of the pandemic

Studies early in the pandemic found that cats shed infectious virus particles and could infect other cats. And during the pandemic, countries have reported SARS-CoV-2 infections in dozens of pet cats. But establishing the direction of viral spread — cat to man or man to cat — is tricky.

They are surprised that it has taken so long to obtain irrefutable proof of effective transmission, given the scale of the pandemic, the ability of the virus to pass from one animal species to another and the close contact between cats and humans. Angela Bosco-Lauth, an infectious disease researcher at Colorado State University in Fort Collins, says in an article linked to the primary publication: “ We knew it was a possibility for two years “.

A fortuitous and rare discovery

The authors have precisely established the chronology of the facts, in order to determine whether indeed the contamination by SARS-CoV-2 was indeed due to the fact of close contact with a cat. In order to support the hypothesis established by the simple chronology, they then compared the genomes of the viruses present in the veterinarian and in the cat.

In August, a father and son from Bangkok who tested positive for SARS-CoV-2 were moved to an isolation ward at Prince of Songkla University Hospital due to unavailability of hospital beds. in Bangkok. Their ten-year-old cat was sent to the University Veterinary Hospital for an examination. He was swabbed and tested positive. For the examination, three veterinarians were present, but only one carried out the test. As the cat was being swabbed, it sneezed in front of a vet, who was wearing a mask and gloves but no eye protection.

Three days later, the vet developed a fever, runny nose and cough, and later tested positive for SARS-CoV-2, but none of her close contacts or the two vets also present during the examination have not developed COVID-19. This suggests that she was infected by the cat when he sneezed. Then, genetic analysis confirmed that the vet was infected with the same variant as the cat and its owners, and the viral genomic sequences were identical.

Phylogenetic tree of SARS-CoV-2 genome sequences of the veterinarian, father and son, and of the cat belonging to them (yellow shading), compared to reference sequences of COVID-19 patients from the province of Songkhla (Thailand), for July-September 2021. © T. Sila et al., 2022 (modified by Laurie Henry for Trust My Science)

Therefore, the authors established the chain of transmission of SARS-CoV-2 infections in this cluster from Bangkok. As mentioned earlier, cats are known to be susceptible to SARS-CoV-2 infection, especially when interacting closely with sick humans. Because infected cats have relatively short incubation and contagion periods, the study cat had probably contracted its infection no more than a week before transmitting the disease to the veterinarian.

Nevertheless, the scientists moderate the conclusions of their report. Indeed, the incidence of this route of transmission is relatively rare due to the short duration (approximately 5 days) during which cats shed viable virus. Nevertheless, to avoid the transmission of SARS-CoV-2 from humans to cats, the authors emphasize that people who test positive for COVID-19 must refrain from all contact with their cat. Additionally, eye protection is strongly recommended for caregivers in close interactions with cats suspected of being infected.

We know that other animals are suspected of infecting humans, such as farmed mink, hamsters and wild deer. Adding cats to the list expands our understanding of the zoonotic potential of this virus “, explains Leo Poon, virologist at the University of Hong Kong.

In conclusion, these events of transmission to humans are rare, animals do not yet play a significant role in the spread of the virus. Bosco-Lauth concludes: Humans are clearly still the main source of the virus “. Humans should take care of their pets instead of getting rid of them at the slightest opportunity (especially with the holidays coming up), while taking care of the nature around them.

Source: Emerging Infectious Diseases

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