Epidemiological Investigation and Genetic Evolution Analysis of Feline Calicivirus during 2025–2026 in Shandong Province

Abstract Feline calicivirus (FCV) is a major viral pathogen associated with feline respiratory diseases. To characterize the epidemiological and evolutionary features of FCV in Shandong Province, China, 656 clinical feline specimens were collected during 2025–2026. RT-PCR was used to screen for common feline viral pathogens, and FCV-positive samples were subjected to virus isolation, purification and whole-genome sequencing. The overall FCV-positive rate was 1.67% (11/656). Co-infections predominated among FCV-positive specimens, with feline parvovirus (FPV) as the most frequent co-infecting agent. Eleven local FCV strains were isolated; genogroup analysis showed that both GI (six strains) and GII (five strains) were circulating. Four high-confidence recombination events were identified. Notably, strain F1481 (genogroup GI) originated from inter-genogroup recombination between a GII-type isolate (F1506) and a GI-type isolate (F1498), providing bioinformatic evidence for natural inter-genogroup recombination between GI and GII FCV strains. These findings indicate that recombination and antigenic drift are important evolutionary forces shaping local FCV populations and provide empirical evidence for regional disease control and the development of geographically matched vaccine candidates.