Isolation, Molecular Characterization, and Pathogenicity Evaluation of a Genotype GI Feline Calicivirus with an Attenuated Phenotype

Feline calicivirus (FCV) is a highly heterogeneous pathogen and a primary cause of feline upper respiratory tract disease, necessitating continuous surveillance to track its evolutionary dynamics. In this study, a novel FCV strain, designated HN/ZZ/2025, was isolated from a cat trading market in Zhengzhou, China, and phylogenetically assigned to genotype GI. Comprehensive biological characterization using CRFK, F81, and Fc3Tg cell lines revealed efficient replication kinetics and typical calicivirus morphology, while genomic analysis identified distinct amino acid substitutions within the hypervariable E region of the VP1 capsid protein. Experimental feline infection induced characteristic clinical symptoms, including pyrexia, weight loss, and oral ulceration, accompanied by persistent viral shedding and systemic dissemination to the kidneys, spleen, and respiratory tract; however, the lack of mortality confirms an attenuated, low-pathogenicity profile compared to virulent systemic FCV variants. These findings offer critical insights into the molecular epidemiology, tissue tropism, and host–virus interactions of circulating FCV strains, providing a robust framework for improving diagnostic surveillance and future vaccine development strategies.