Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, belongs to the same species as the virus responsible for the SARS epidemic of 2003. The novel virus emerged in December 2019, in Wuhan, China, likely from bats, although some theories suggest that an intermediate species might have been involved.
Studies about the current COVID-19 pandemic have shown that SARS-CoV-2 infections can be transmitted from humans to domestic and non-domestic cats, dogs, and mink. Some in vivo experiments also show that while SARS-CoV-2 can infect ferrets, cats, and hamsters, other animals such as ducks, pigs, and chickens are not susceptible to the virus.
Cat-to-cat transmission of SARS-CoV-2 has been experimentally proven, but little is known about the significance of this novel virus as a feline pathogen or its reverse zoonotic potential. The establishment of new animal reservoirs of SARS-CoV-2 could pose serious problems for human health in the future.
Currently, we do not have evidence of cat-to-human transmission or that dogs, cats, or other pets play any significant role in the epidemiology of SARS-CoV-2 in humans. Although it is clear that the current pandemic is driven by human-to-human transmission, it is important to determine if domestic animals can get infected and if they pose any risk to humans, especially those with comorbidities who are more likely to progress to severe disease.
Domestic animals could also serve as a viral reservoir, thus enabling continued transmission of the virus, even when human-to-human transmission slows down. Recent studies from Dutch mink farms that reported both mink-to-cat and mink-to-human transmission of SARS-CoV-2 agree with this scenario.
“Although the ongoing SARS-CoV-2 pandemic is driven by human-to-human transmission, concerns have been raised that other species might have the potential to play a role by becoming a new reservoir for the virus.”
In a study published on the preprint server bioRxiv,* a team of researchers from the University of Glasgow used a combination of lab techniques to show that two domestic cats from households with positive COVID-19 cases showing symptoms of mild to severe respiratory disease were infected with SARS-CoV-2.
Lung of a cat infected with SARS CoV-2; a positive signal for nucleocapsid protein (green signal) was detected within the cytoplasm of the bronchiolar epithelium (A; bar, 10 µm) and viral RNA (red dots) of the spike gene was detectable in alveolar membranes (B; bar, 100 µm; haematoxylin counterstain).
Feline lung tissue tested positive for SARS-CoV-2 antigen and RNA
Two cats from different households in the UK with COVID-19 infection were studied using immunofluorescence, reverse transcriptase quantitative PCR, in situ hybridization, and viral genome sequencing. The lung tissue of cat 1 collected post-mortem showed pathological and histological findings consistent with viral pneumonia and also tested positive for SARS-CoV-2 RNA and antigens.
An oropharyngeal swab from cat 2 had viral RNA, and the cat showed signs of rhinitis and conjunctivitis. High throughput sequencing of the virus collected from cat 2 showed that the feline viral genome had 5 single nucleotide polymorphisms compared to the closest UK human SARS-CoV-2 sequence. A study comparing the viral genome from cat 2 with 9 other cat-derived SARS-CoV-2 sequences from various parts of the world showed no shared mutations.
The findings of the team confirmed that human-to-cat SARS-CoV-2 transmission is possible and can cause signs of respiratory disease in cats.
Findings highlight the need for a One Health approach
Previous reports of human-to-pet transmission of the SARS-CoV-2 virus have been sporadic might be because animal testing is limited. These reports underestimate the actual frequency of human-to-pet transmission. Reverse zoonotic transmission of SARS-CoV-2 represents a comparatively low risk to animal or public health in areas where transmission from human to human remains high.
Based on these findings of the study, the University of Glasgow team concluded that human-to-cat transmission of SARS-CoV-2 virus happened in the UK during the COVID-19 pandemic, with the cats developing mild to severe respiratory disease. The findings provide crucial insights into the management of cats by people who are at risk of developing severe disease.
Although we currently do not have evidence to show that domestic cats have any role in the epidemiology of the COVID-19, a better understanding of human-to-cat transmission mechanisms is possible only by monitoring cats in COVID-19-infected households.
“It will be important to investigate whether cat-to-human transmission is possible or likely, and to determine the duration of virus shedding and the level of contact with humans that is required for transmission to occur.”
The researchers feel that keeping in mind the versatility of the novel coronavirus, it is crucial to monitor cat-to-cat, human-to-cat, and cat-to-human transmission of the virus. The two reverse zoonotic infections reported in this study emphasize the need for a One Health approach between public health and veterinary organizations.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Respiratory disease in cats associated with human-to-cat transmission of SARS-CoV-2 in the UK Margaret J Hosie, Ilaria Epifano, Vanessa Herder, Richard Orton, Andrew Stevenson, Natasha Johnson, Emma MacDonald, Dawn Dunbar, Michael McDonald, Fiona Howie, Bryn Tennant, Darcy Herrity, Ana C Filipe, Daniel G Streicker, Brian J Willett, Pablo R Murcia, Ruth F Jarrett, David L Robertson, William Weir, COVID-19 Genomics UK Consortium bioRxiv 2020.09.23.309948; doi: https://doi.org/10.1101/2020.09.23.309948, https://www.biorxiv.org/content/10.1101/2020.09.23.309948v1