A feline calicivirus strain confers broad immunity

Feline calicivirus (FCV) typically causes severe respiratory infections and oral ulcers in cats, posing a significant threat to feline health. However, the high variability of FCV presents serious challenges to vaccine development and drug treatment. Currently available vaccines may not provide complete protection; thus, the need to screen for novel broad-spectrum vaccine strains to enhance cross-protection against multiple genotypes is urgent. This study successfully established animal models with a 100% disease incidence in genotypes GI and GII by isolating and identifying 56 endemic FCV strains from China and assessing the pathogenicity of different genotypes. We further evaluated the immunogenicity of 56 FCV strains and identified the dominant strain, FCV WH24, which exhibited the greatest immunogenicity and was found to elicit broad cross-neutralizing antibodies against heterologous strains. Moreover, in in vivo challenge experiments, the FCV WH24 immunization group showed good protection against both the GI and the GII FCV genotypes. Furthermore, in this study, the neutralizing antibody protection threshold was determined to be 2 6 . Genetic phylogenetic analysis was performed on 56 isolated FCV strains, along with NCBI reference strains and commercially available vaccine strains. The two major genotypes, GI and GII, were further subdivided into 14 groups. One strain was randomly selected from each group as a representative strain to verify the broad-spectrum neutralizing activity of FCV strain WH24, which showed a protection rate of 85.7% against FCV, compared with only 42.9% for commercially available vaccines. This study identified a broad-spectrum vaccine candidate strain, FCV WH24, which exhibits excellent cross-protective potential against both GI and GII FCV types. It holds promise as a novel vaccine strain and provides an important reference for subsequent FCV vaccine development.