Serological Study of SARS-CoV-2 Antibodies in Japanese Cats: Analysis of Risk Factors Among Cat Lifestyles

Background Little is known about the epidemic status of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in cats living in Japan, and about the influence of cat lifestyles on the SARS-CoV-2 infection epidemic in cats. Results We developed protein A/G-based ELISA, which was standardized using positive rabbit antibodies. The measured values of this ELISA were consistent with those of conventional anti-feline IgG-based ELISA. We then collected blood samples from 1,969 cats that visited veterinary clinics in Japan from June to July 2020 and examined for the presence of anti-SARS-CoV-2 antibodies. Using protein A/G-based ELISA, nine cats were found to have SARS-CoV-2 S1-specific IgG, among which four had RBD-specific IgG. Among those nine samples, one showed neutralizing activity. Based on these, we estimated that the prevalence of SARS-CoV-2 neutralizing antibodies in cats living in Japan was 0.05% (1/1,969 samples). This prevalence did not differ much from the prevalence of neutralizing antibodies for SARS-CoV-2 in humans conducted in Japan at that time. Furthermore, we searched for factors associated with the prevalence of neutralizing antibodies in cats using our data and information from five countries (China, Croatia, France, Germany, and Italy). The prevalence of SARS-CoV-2 in cats was correlated with the rate of keeping indoor-only. Conclusions Protein A/G-based ELISA has the potential to be a standardized method to measure anti-SARS-CoV-2 antibodies in cats. The infection status of SARS-CoV-2 in cats in Japan is linked to that in humans, and the epidemic of SARS-CoV-2 infection in cats may be controlled by their living environment.