SARS-CoV-2 in UK domestic cats
5 July 2023
THE AIMS OF THE STUDY
In late 2019, a novel coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), emerged, resulting in a global pandemic and causing substantial threat to public health. SARS-CoV-2 is highly transmissible in humans, but other species, such as felids, are also susceptible. Although domestic cats are not frequently tested for SARS-CoV-2 in the UK, several studies show that they can become infected via close contact with infected people or other infected cats. Like humans, cats can mount neutralising antibody responses against SARS-CoV-2 that block viral entry and resist reinfection, but the characteristics of these immune responses are still poorly understood.
At the MRC-University of Glasgow Centre for Virus Research (Glasgow, UK), Professor Margaret Hosie and PhD student Grace Tyson are working on uncovering the nature of the feline antibody response to SARS-CoV-2 in the UK. In June 2022, I joined their team as a BVMS summer research student to investigate the presence, strength, and cross-neutralising ability of feline antibodies against four different SARS-CoV-2 pseudotypes (B.1, Alpha, Delta, and Omicron BA.1) using pseudotype-based neutralisation assays on residual serum samples collected in the spring and summer of 2022.
WHAT WE LEARNED FROM THE STUDY
Thirty-two of 806 cats (4%) sampled between February 1 and July 7, 2022, tested positive for SARS-CoV-2 neutralising antibodies. This corresponds to a small decline in seroprevalence compared to earlier phases of the pandemic (e.g., 5% in winter 2021-2022). Neutralising antibody titres also tended to decrease in more recent seasons. A decrease in seroprevalence and neutralising antibody titres may reflect waning immunity.
Spring-Summer 2022 was a time period characterized by the Omicron wave in the UK’s human population, but most newly detected seropositive cats had higher neutralising antibodies against B.1, Alpha, and Delta variants, and significantly lower titres against Omicron. This suggests that the neutralising antibody response against older variants is either long-lived or boosted by subsequent infections, and that either responses against Omicron are weak or fewer cats are infected with Omicron.
Twenty-four of 32 seropositive samples (75%) produced neutralising antibody titres against more than one
SARS-CoV-2 pseudotype. This suggests that antibodies produced in response to SARS-CoV-2 infection can
recognise and target viral variants with slight antigenic differences. But cross-neutralisation was stronger between B.1, Alpha, and Delta variants, and weaker with Omicron. Because several mutations within the Omicron RBD are associated with decreased antibody binding for neutralisation in human studies, existing antibodies produced by older variants may not recognize and target Omicron very well. Previously infected cats may therefore be vulnerable to reinfection when exposed to newer SARS-CoV-2 variants.
We also found that likelihood of seropositivity was not associated with sex, age, or pedigree of cats, which means that all feline demographic groups should be treated as equally susceptible to SARS-CoV-2 infection.
Our ability to detect seropositivity in 4% of cats sampled is significant given that we were not actively seeking out cats from COVID-positive households. Our study utilised residual serum samples sent to the University of Glasgow’s Veterinary Diagnostic Services laboratory for routine testing for conditions unrelated to suspected SARS-CoV-2 infection, therefore our data potentially underestimates the overall seropositivity of domestic cats in the UK. While the data were diverse, cats visiting veterinary clinics and getting their blood drawn for testing are more likely to be unwell, suffering from underlying medical conditions, and at higher risk of contracting infectious diseases. Pedigree cats are also often overrepresented in veterinary clinics. Therefore, our study population is not fully representative of the UK feline population. Additionally, it cannot be concluded that SARS-CoV-2 seropositive cats have been infected via contact with their infected owners without infection history and sequence data from individual households, which was not possible in this study.
WHY IS THIS RESEARCH IMPORTANT?
Information about current seroprevalence and antibody responses in cats can help veterinarians include SARS-CoV-2 as a possible differential diagnosis, understand how their patients might be affected by new circulating variants, encourage submission of samples for SARS-CoV-2 testing, and help increase pet-owner awareness.
These findings also reinforce the importance of following the recommendations of the European Advisory Board on Cat Diseases to avoid close contact with cats when testing positive for SARS-CoV-2, maintain good hygiene when handling their supplies, and keep cats from positive households indoors to prevent spread. Additionally, adopting a One-Health strategy that involves monitoring both humans and their pets could help to control the COVID-19 pandemic, given the concerns about animal infections spilling back to humans.
CONSIDER PETSAVERS FOR YOUR RESEARCH
This project was supported by an award from BSAVA PetSavers, which helped cover the cost of the stipend and lab consumables required to fill the gap in knowledge in our understanding of antibody responses to SARS-CoV-2 in UK domestic cats. Similar types of projects investigating small animal diseases using residual samples lend themselves well to PetSavers-funded research. Not only does PetSavers financially support student projects, but they also facilitate opportunities for professional growth via publication of findings and participation at the annual BSAVA Congress. I strongly encourage fellow UK veterinary students to consider their Student Research Project (SRP) funding option.
ABOUT THE AUTHOR
I am a third-year veterinary student at the University of Glasgow School of Biodiversity, One Health & Veterinary Medicine. My experiences prior to vet school formed the foundation for my current interests. Early on, I worked with NGOs, wildlife rescue centres, and conservation programs in Canada and New Zealand which helped me consider the broad ecological perspectives of animal health and disease. During my BSc, I completed an Honours Research Project studying behavioural syndromes in wild songbirds. During my MSc, I studied stress physiology and parental care in wild songbirds, and after graduation, I worked as an ecology research technician at CNRS’s biology station in Midi-Pyrénées, France. These experiences helped focus my ambitions to pursue a career in animal health and welfare. During vet school, at the height of the COVID-19 pandemic, my interests for infectious diseases, pathology, and veterinary diagnostics flourished. This unique moment in history created an opportunity to study how our household pets respond to SARS-CoV-2 infections, and I jumped on the opportunity to participate. I am grateful to have worked alongside such a dedicated and hardworking team of researchers at the University of Glasgow’s Centre for Virus Research.
In participating in this research project, I gained a deeper understanding of immune responses to viral infections, gained valuable experience in molecular laboratory techniques, and practised science communication. These skills will be invaluable for my progression from veterinary student to veterinary practitioner as I hope to continue exploring the field of pathology and disease investigation in the future.