Co-circulation and evolution of genogroups I and II of respiratory and enteric feline calicivirus isolates in cats

Feline calicivirus (FCV) is a highly infectious pathogen that causes upper respiratory tract disease (URTD), but the enteric FCVs raise concerns regarding their role of an enteric pathogen. In this study, between 2019 and 2020, 101 clinical samples from domestic cats with symptoms of URTD, with or without enteritis, were collected for FCV-specific detection. The FCV-positive rate reached to 42.4% (28/66) in cats with respiratory symptoms. The rates were 11.1% (3/27) and 12.5% (1/8) when faeces and serum samples were measured using reverse transcription polymerase chain reaction (RT-PCR), respectively. Ten FCV strains were successfully isolated from respiratory and enteric sources in domestic cats from Guangxi. Phylogenetic analysis based on the genome sequences of 11 isolates (including GX01-13 isolated in 2013) indicated that the newly characterized FCV strains had two recombinant events in comparison with other FCVs and were of respiratory and enteric origins. These strains displayed high genetic diversity, and they were divided into two genogroups (I and II). Of these, the GXNN02-19 isolate was grouped with previously published Chinese isolates that were identified as genogroup II, which contained three specific amino acid residues (377K, 539V and 557S) in the VP1 protein. In addition, the three enteric viruses appeared genetically heterogeneous to each other. All isolates were found to be more sensitive when exposed to low pH conditions, but they were resistant to treatment with trypsin and bile salts. Furthermore, there were no significant differences between the respiratory and enteric FCVs. Our results showed that the genetically distinct FCV strains with genogroups I and II from respiratory and enteric origins were co-circulating in this geographical area. Also, it was revealed that the potential recombinant events between the enteric and respiratory FCVs suggested an important role of enteric FCV during the evolution.