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 can serve as a natural reservoir for the virus, in order to understand the mechanism of spread, on the one hand, within the species and, on the other, through different taxa. The objective is to prevent any zoonosis, that is, 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 after the pandemic, an apparently 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 the researchers monitored this closely.

Ever since the virus began to spread around the world, scientists have feared that it could jump from humans to wild animals, meaning it could hide among various animal populations and eventually mutate and reappear in humans even after it ends. of the pandemic.

Wild animals aren’t the only ones that attract 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 beginning of the pandemic

Studies early in the pandemic found that cats shed infectious viral particles and can 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 – from cat to man or from man to cat – is tricky.

They are surprised that it took so long to obtain irrefutable evidence 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 accurately established the chronology of the facts in order to determine if indeed the SARS-CoV-2 contamination was in fact due to close contact with a cat. 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 Bangkok father and son who tested positive for SARS-CoV-2 were transferred to an isolation ward at Prince of Songkla University Hospital due to unavailability of hospital beds in Bangkok. His ten-year-old cat was sent to the University Veterinary Hospital to be examined. He was tested and came back positive. For the examination, three veterinarians were present, but only one performed the test. As the cat was being scrubbed, he sneezed in front of a veterinarian, 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 his close contacts or the two vets also present during the exam did not develop 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 from veterinarian, father and son, and the cat belonging to them (shaded yellow), compared to reference sequences from COVID-19 patients from Songkhla Province (Thailand), for July-September 2021. © T. Sila et al., 2022 (modified by Laurie Henry for Trust My Science)

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

However, the scientists moderate the conclusions of their report. In fact, the incidence of this route of transmission is relatively rare due to the short duration (approximately 5 days) in which cats shed viable virus. However, to prevent transmission of SARS-CoV-2 from humans to cats, the authors emphasize that people who test positive for COVID-19 should refrain from any contact with their cat. In addition, 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, a virologist at the University of Hong Kong.

In conclusion, these transmission events to humans are rare, animals still do not 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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