Genetic Diversity and Biological Characteristics of a Novel Feline Calicivirus Strain Isolated From Zoo-Captive South China Tiger (Panthera tigris amoyensis).

Feline calicivirus (FCV) is a common pathogen causing upper respiratory tract disease in domestic cats. Nonetheless, its threat and genetic features in endangered wild felids remain poorly understood. In this study, a novel FCV strain from a captive South China tiger (Panthera tigris amoyensis) was isolated, designated as FCV LYH1224. Viral RNA was detected in multiple tissues of the deceased tiger, including the heart, liver, spleen, lungs, and kidneys, suggesting broad tissue tropism and FCV contributed substantially to the fatal outcome. In vitro growth kinetics showed that the virus replicates efficiently in Crandell-Rees feline kidney (CRFK) cells. Whole-genome sequencing and phylogenetic analysis indicated that it was classified as genotype II (GII) and exhibited unique evolutionary lineages. Within GII, it clusters closely with the previously reported tiger-derived strain FCV-YH/16 but exhibits an independent branch in the VP1 gene tree, suggesting complex genetic variation among FCV strains from diverse wildlife origins. Sequence identity analysis indicated that FCV LYH1224 was genetically distant from vaccine strains F9 and 2280, with whole-genome nucleotide identity of 76.6% and 77.0%, respectively. Notably, the VP1-E region displayed the lowest identity, with nucleotide identity of 68.1% and 66.7%, respectively. Analysis of key amino acid residues revealed distinct substitutions within the neutralizing epitope (aa 445-451) and common mutations at virulence-related positions 452A and 492I, which were absent in reference strains, suggesting potential antigenic diversity and host-specific adaptations. This study provides a comprehensive genomic characterization of FCV strain in South China tigers, highlighting the genetic diversity and distinctive antigenic properties observed in this isolate compared with existing strains. The considerable genetic divergence from vaccine strains emphasizes the importance of ongoing surveillance and the inclusion of wildlife-derived strains in vaccine development strategies.