First report of molecular epidemiology and phylogenetic characteristics of feline herpesvirus (FHV-1) from naturally infected cats in Kunshan, China.

BACKGROUND: Feline herpesvirus type 1 (FHV-1) is a life threatening highly contagious virus in cats and typically causes upper respiratory tract infections as well as conjunctival and corneal ulcers. Genetic variability could alter the severity of diseases and clinical signs. Despite regular vaccine practices against FHV-1 in China, new FHV-1 cases still commonly occur. The genetic and phylogenetic characteristics of FHV-1 in Kunshan city of China has not been studied yet. Therefore, this study was planned to investigate the prevalence, molecular characteristics of circulating strains, and phylogenetic analyses of FHV-1. This is the first report of molecular epidemiology and phylogenetic characteristics of FHV-1 from naturally infected cats in Kunshan, China. METHODS: The occulo-nasal swabs were collected from diseased cats showing respiratory distress, conjunctivitis, and corneal ulcers at different veterinary clinics in Kunshan from 2022 to 2023. Clinical data and general information were recorded. Swab samples were processed for preliminary detection of FHV-1. Thymidine kinase (TK), glycoprotein B (gB) and glycoprotein D (gD) genes were sequenced and analyzed to investigate genetic diversity and evolution of FHV-1. RESULTS: The FHV-1 genome was detected in 43 (43/200, 21.5%) samples using RT-PCR targeting the TK gene. Statistical analysis showed a significant correlation between age, vaccination status and living environment (p < 0.05) with FHV-1 positivity, while a non-significant correlation was observed for FHV-1 positivity and sex of cats (p > 0.05). Additionally, eight FHV-1 positive cats were co-infected with feline calicivirus (8/43,18.6%). FHV-1 identified in the present study was confirmed as FHV-1 based on phylogenetic analyses. The sequence analyses revealed that 43 FHV-1 strains identified in the present study did not differ much with reference strains within China and worldwide. A nucleotide homology of 99-100% was determined among gB, TK and gD genes nucleotide sequences when compared with standard strain C-27 and vaccine strains. Amino acid analysis showed some amino acid substitutions in TK, gB and gD protein sequences. A potential N-linked glycosylation site was observed in all TK protein sequences. Phylogenetic analyses revealed minor variations and short evolutionary distance among FHV-1 strains detected in this study. CONCLUSIONS: Our findings indicate that genomes of 43 FHV-1 strains are highly homogenous and antigenically similar, and the degree of variation in major envelope proteins between strains is low. This study demonstrated some useful data about prevalence, genetic characteristics, and evolution of FHV-1 in Kunshan, which may aid in future vaccine development.

Molecular epidemiology and phylogenetic analysis of feline calicivirus in Kunshan, China.

Feline calicivirus (FCV) is a highly contagious virus in cats, which typically causes respiratory tract and oral infections. Despite vaccination against FCV being a regular practice in China, new FCV cases still occur. Antigenic diversity of FCV hinders the effective control by vaccination. This is first report which aims to investigate the molecular epidemiology and molecular characteristics of FCV in Kunshan, China. The nasopharyngeal swabs were collected from cats showing variable clinical signs from different animal clinics in Kunshan from 2022 to 2023. Preliminary detection and sequencing of the FCV capsid gene were performed to study genetic diversity and evolutionary characteristics. FCV-RNA was identified in 52 (26%) of the samples using RT-PCR. A significant association was found between FCV-positive detection rate, age, gender, vaccination status and living environment, while a non-significant association was found with breed of cats. Nucleotide analysis revealed two genotypes, GI and GII. GII predominated in Kunshan, with diverse strains and amino acid variations potentially affecting vaccination efficacy and FCV detection. Notably, analysis pinpointed certain strains' association with FCV-virulent systemic disease pathotypes. This investigation sheds light on FCV dynamics, which may aid in developing better prevention strategies and future vaccine designs against circulating FCV genotypes.