first documented case of transmission of SARS-CoV-2 from cats to humans – Biomedical Realities

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This is the story of a Thai veterinarian 32-year-old who presented himself on August 15, 2021 at the university hospital of Songkhla, a city located in the south of the country. She has had a fever, a clear runny nose and a productive cough for two days. She tells doctors that she and two of her colleagues examined a cat brought by two men to the university veterinary hospital where she practices.

The two men, who reside in Bangkok, are a father and son, aged 64 and 32 respectively. They have a cat who used to sleep with them.

On August 7, both were diagnosed positive for the SARS-CoV-2 coronavirus. Symptoms of Covid-19 began on August 4.

On August 8, the father and his son were transported from Bangkok to Songkhla by ambulance. They are transferred to the Prince of Songkhla hospital, 900 km away, because there are no more beds available in the hospitals of the capital. Their cat is part of the trip which lasts 20 hours. Upon arrival, the two patients were immediately placed in hospital isolation, while the cat was taken to a university veterinary clinic for examination on August 10.

The clinical state of the animal does not inspire any concern. The 32-year-old veterinarian takes a nasopharyngeal and rectal swab from the feline, while two of her colleagues hold the animal. During the nasal swab, the animal sneezes in the face of the veterinarian. She and her two assistants are wearing disposable gloves and an FFP2 mask. None of the three veterinarians is equipped with a visor or goggles. The face-to-face with the animal lasted about ten minutes.

On August 13, three days after being in close contact with the cat, the young female veterinarian began to show symptoms. She does not consult immediately. It was not until August 15 that she decided to go to the hospital where she learned that the results of the RT-PCR test carried out on the nasal and rectal swab of the cat she had examined were positive for SARS. -CoV-2*. The veterinarian’s nasopharyngeal swab is also positive for the coronavirus.

The veterinarian, as well as the two men who own the cat, then find themselves in isolation in the hospital. RT-PCR tests performed on the vet’s two colleagues are negative for SARS-CoV-2.

Epidemiological and genomic surveys

An epidemiological investigation (contact tracing) is immediately carried out among the 30 people working at the veterinary hospital. It is then that the existence of a case of Covid-19 is detected in another veterinarian practicing in another service, in this case the one which takes care of large animals. On August 13, this patient developed a fever and tested positive for SARS-CoV-2, the day before the cat was examined. This person had no direct or indirect contact with the cat or his three other veterinary colleagues.

Molecular biologists then undertook to sequence the viral genome from samples taken from the cat and the four veterinarians, as well as from other Covid-19 patients in Songkhla province. They thus succeed in constructing a phylogenetic tree, making it possible to establish the genetic relationship between the genomic sequences. It turns out that the viral genomes found in the father, the son, and their cat are identical to those identified in the young female veterinarian. On the other hand, the sequences differ from those identified in other Covid-19 patients residing in the same province.

The identity of the genomic sequences obtained from the veterinarian, the cat and its two owners, as well as the temporality of the symptoms between the infections observed in humans and the feline, shows the existence of an epidemiological link between the contaminations.

The study authors point out that the veterinarian had never previously met the father and son, owners of the cat. She was probably contaminated when the cat sneezed on her face. Similarly, the genomic sequences identified in his nasopharyngeal sample differ from those from the biological samples of his colleague infected in the same veterinary hospital and who had presented the first symptoms of Covid-19 four days earlier.

Several studies, published in 2020 in the Proceedings of the American Academy of Sciences (PNAS)the New England Journal of Medicine and the review Sciencehave shown that cats can be infected with SARS-CoV-2, especially during close contact with infected and symptomatic patients.

Infected cats have a relatively short incubation period. The duration of contagiousness is also short. Studies have shown the presence of SARS-CoV-2 RNA in the nasal cavities of these felines for a period generally not exceeding five days. It is therefore likely that the cat contracted the infection less than a week before transmitting SARS-CoV-2 to the veterinarian who examined him.

The authors believe that animal-to-human transmission occurred when the cat sneezed when it was very close to the vet. According to Tanit Sila and colleagues from Songkhla University Faculty of Medicine, who reported this case in an article posted online on June 6, 2022 in the journal Emerging Infectious Diseases, the contamination of the veterinarian, protected by an FFP2 mask and gloves, undoubtedly took place through the eyes. She wore gloves and washed her hands before and after examining the animal, but did not wear eye protection. Thereby, “the ocular surface was vulnerable to infection via droplets expelled by the cat”, say the authors.

According to them, the vet’s infection underscores the importance of wearing goggles or a face shield in addition to a mask when interacting closely with cats suspected of being infected.

“In summary, we have provided evidence that cats can transmit SARS-CoV-2 infection to humans. However, the incidence of this mode of transmission is relatively rare due to the short duration (median of 5 days) in which cats shed viable virus. Nevertheless, to prevent transmission of SARS-CoV-2 from humans to cats, people with suspected or confirmed Covid-19 should refrain from contact with their cat,” conclude the authors.

A final word: the veterinarian, as well as the owners of the cat, left the hospital one to two weeks after their admission and remained isolated at home for 28 days.

Mark Gozlan (Follow me on TwitterFacebook, LinkedInand on my new blog ‘Diabetes in all states’, devoted to the thousand and one facets of diabetes. Already 13 tickets)

* The viral load present in the nasal and rectal swab from the cat was found to be elevated as the Ct (Cycle threshold) was relatively low (respectively 17 and 21 in the PCR reaction targeted on the ORF1ab gene and 16 and 15 in the PCR reaction targeted on the N gene). It is recalled that the Ct is the number of amplification cycles to reach the detection threshold during the PCR reaction. The lower the Ct value, the more virus there is in the sample analyzed.

To know more :

Sila T, Sunghan J, Laochareonsuk W, et al. Suspected Cat-to-Human Transmission of SARS-CoV-2, Thailand, July-September 2021. Emerg Infect Dis. 2022 Jul;28(7):1485-1488. doi: 10.3201/eid2807.212605

Bosco-Lauth AM, Hartwig AE, Porter SM, et al. Experimental infection of domestic dogs and cats with SARS-CoV-2: Pathogenesis, transmission, and response to reexposure in cats. Proc Natl Acad Sci US A. 2020 Oct 20;117(42):26382-26388. doi: 10.1073/pnas.2013102117

Halfmann PJ, Hatta M, Chiba S, et al. Transmission of SARS-CoV-2 in Domestic Cats. N Engl J Med. 2020 Aug 6;383(6):592-594. doi: 10.1056/NEJMc2013400

Shi J, Wen Z, Zhong G, et al. Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS-coronavirus 2. Science. 2020 May 29;368(6494):1016-1020. doi: 10.1126/science.abb7015

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