Discovery of a novel genogroup feline calicivirus through molecular evolution in group-housed cats in China.

Feline calicivirus (FCV) is a highly infectious pathogen that causes upper respiratory tract disease (URTD), with a higher prevalence in group-housed cats compared to those raised individually. In this study, 15 FCV strains were isolated from group-housed cats exhibiting URTD symptoms in Changzhou, China, in 2024. Phylogenetic analysis based on the VP1 sequences revealed that 13 of 15 strains clustered within genogroup I (G I), while none belonged to genogroup II (G II). Notably, the remaining two strains grouped with several recently published Chinese isolates, forming an independent branch distinct from both G I and G II, proposed as genogroup III (G III). The VP1 proteins of the 13 G I strains exhibited specific residues 377N, 539A, and 557G, consistent with the established G I-specific markers (377N/S, 539A/P, and 557G). In contrast, G II strains typically retain 377 K, 539 V, and 557S. Interestingly, the G III strains displayed 377N, 539A (specific to G I) and 557S (specific to G II). Recombinant analysis found that co-circulating G I and G III resulted in a recombinant strain. Furthermore, neutralization tests demonstrated poor cross-neutralization between G I and G III strains. This study provides valuable insights for the development of effective vaccination strategies.