In a recent study published in the United States (U.S.) Centers for Disease Control and Prevention’s (CDC) Emerging Infectious Disease Journal, researchers from Scotland tested the seroprevalence and antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in pet cats in the United Kingdom (U.K.).

Study: SARS-CoV-2 Seroprevalence and Cross-Variant Antibody Neutralization in Cats, United Kingdom. Image Credit: AfricaStudio/Shutterstock.com

Background

Since the onset of the coronavirus disease 2019 (COVID-19) pandemic, the World Health Organization (WHO) has reported that about 26 animal species are believed to be susceptible to SARS-CoV-2 infections.

Determining the susceptibility of animal species to SARS-CoV-2 is important to understand the risk of onward transmission of the virus within animal populations and the probability of animal populations serving as viral reservoirs.

Studies have reported animal-to-animal transmission within hamster, mink, and white-tailed deer populations.

Felids comprise approximately 30% of species believed to be susceptible to SARS-CoV-2. However, whether pet cats, which frequently come in close contact with humans, are susceptible to the different variants of SARS-CoV-2 and whether or not cats develop clinical symptoms of SARS-CoV-2 infections remains unclear.

About the study

In the present study, the researchers used enzyme-linked immunosorbent assay (ELISA) to measure the antibodies against the SARS-CoV-2 spike protein receptor binding domain and pseudoviral neutralization assay (PVNA) to determine the neutralizing antibody titers in pet cats between April 2020 and February 2022.

The viral pseudotypes comprised a lentiviral backbone and the spike proteins of the dominant circulating SARS-CoV-2 variants in the U.K.

Blood samples from 2,309 domestic cats were screened using ELISA and PVNA; the pseudotypes comprised spike proteins from the ancestral strain (D614G) and the Alpha, Delta, and Omicron variants.

Results

The results indicated that with time, the SARS-CoV-2 seroprevalence increased in domestic cats in the U.K., the seroprevalence being the highest between September and November 2021 (5.3%), and between December 2021 and February 2022 (5.2%).

Furthermore, the viral titers showed variant-specific differences between individual samples, with 41.3% having the highest antibody titers against the Alpha variant, 36% being Delta dominant, and 22.7% having the highest antibody titers against the ancestral strain.

When the pseudotyped viruses were used to determine the neutralization titers, the Delta dominant blood samples had higher neutralization titers against the pseudovirus carrying the Delta spike protein.

Since the number of samples collected after the emergence of the Omicron variant was quite low, no seropositive samples that were Omicron-dominant were found.

While the emergent variants were detected in cats only after they were detected in humans, significant neutralizing antibody titers against extinct SARS-CoV-2 variants were found in cats, despite a decline in the number of human cases due to that variant.

The cross-variant neutralization was also lower, with the neutralizing antibody titers in the Alpha, Delta, Omicron, and D614G dominant samples being lower against all pseudotyped viruses other than their dominant pseudoviruses.

Although the results were insignificant, the study found that the proportion of seropositive pedigree cats was greater than that of non-pedigree cats. The authors believe pedigree cats are more likely to be completely indoors, increasing the contact with owners and the risk of contracting SARS-CoV-2 from humans.

Conclusions

The study evaluated the neutralizing antibody titers and seroprevalence against SARS-CoV-2 among domestic cats in the U.K. to determine the risk of animal-to-animal and animal-to-human transmission.

The results indicated that the SARS-CoV-2 seroprevalence in domestic cats increased during the COVID-19 pandemic in the U.K.

This suggests an increased risk of transmission of emerging SARS-CoV-2 variants from humans to cats and highlights the need to monitor SARS-CoV-2 infections among pet cats that frequently come in contact with their owners.