Serological response to feline coronavirus in the UK domestic cat population

Feline coronavirus (FCoV) is a ubiquitous virus of cats, with highly variable seroprevalence, ranging between 4 and 95% worldwide in the domestic cat population. It is the causative agent of feline infectious peritonitis (FIP), a disease which, prior to the recent introduction of effective antiviral drug treatments, was invariably fatal. The recent outbreak of FIP, originating in Cyprus and caused by the novel recombinant FCoV-23, highlighted the need to increase understanding of the serological response to FCoV. This study aimed to characterize the serological response to the virus and to assess cross-neutralization of type II FCoV subtypes as well as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In serum samples of 1117 UK cats collected between 2020 and 2023, we detected an FCoV-II neutralizing antibody (nAb) seroprevalence of 13.6% and an overall seroprevalence of 59.5%; commonly cited risk factors (sex, age and breed) did not significantly impact the nAb seroprevalence nor nAb titre against FCoV-II. Antibodies against subtypes FIPV-79-1146 and FIPV-DF-2 were found to be cross-reactive and additionally neutralized both isoforms of FCoV-23. In contrast, no cross-neutralization was observed against SARS-CoV-2. Overall, these results highlight that although FCoV infection offers effective cross-protection between FCoV strains and subtypes, this does not extend to betacoronaviruses.