A Virulent Systemic Feline Calicivirus Strain Isolated in China Could Produce Broadly Neutralizing Antibodies Against Multiple Strains

Feline calicivirus (FCV) is a significant pathogen in cats, with sporadic outbreaks of infections with virulent systemic (VS-FCV) strains causing significant health problems. Nineteen FCV strains were isolated and identified in China from 2021 to 2022. The nucleotide and amino acid phylogenetic analysis of the VP1 gene showed that 16 strains were GI genotype and three strains were GII genotype. HBDL2 strain was further found to be in the same clade as the reported VS-FCV SH/2014 strain, with 87.1% nucleotide sequence identity and 93.0% amino acid sequence identity. However, given that phylogenetic and homology analysis alone is insufficient to predict virulence, the pathogenic potential of HBDL2 was subsequently assessed through experimental infection in cats. The results revealed that HBDL2 was able to cause systemic clinical signs and caused severe tracheal and lung damage, with a similar characterization as the VS-FCV strain. Serum neutralization assays confirmed that HBDL2 elicited broad-spectrum neutralizing antibodies in cats against multiple FCV strains, including diverse GI and GII genotypes. Notably, neutralizing antibody titers against the VS-FCV strains were elevated. Additionally, we established an infectious clone of HBDL2 as a critical technical tool. These findings indicate that the HBDL2 strain holds promise for use in vaccine development against FCV infection.