Molecular insights into domestic cat hepatitis B virus linking genome to function.

Domestic cat hepatitis B virus (DCHBV) is a member of the Hepadnaviridae family and has been associated with hepatocellular carcinoma (HCC) in cats. This study aimed to determine the prevalence of DCHBV and associations with feline immunodeficiency virus (FIV), feline leukaemia virus (FeLV) and feline coronavirus (FCoV) infections in cats in Serbia, and to characterise the detected DCHBV genomes. Whole blood, serum and liver samples from 308 animals were screened by real-time (RT-)PCR for DCHBV, FIV, FeLV, and FCoV. The prevalence of DCHBV was 2.60%, with no significant associations observed between DCHBV infection and age, sex, or coinfection status. Three whole genome sequences were obtained, and phylogenetic analysis demonstrated that the Serbian strains belong to genotype A. Molecular analysis revealed three unique nonsynonymous substitutions in the S ORF. Within the C ORF, a 28-amino acid N-terminal precore region with conserved cysteine residues critical for protein maturation was identified, along with the C-terminal arginine-rich domain. A putative core promoter region was detected, containing two motifs analogous to the pgRNA and pcRNA initiator elements described in hepatitis B virus (HBV). DCHBV sequences contained two 11-bp direct repeats with DR2 located in X ORF and DR1 positioned in the C ORF. This study represents the first report of DCHBV in Serbia, providing new insights into its epidemiology and genomic features. The findings expand current knowledge of its molecular diversity and underscore the importance of genomic characterisation for understanding its role in liver disease development.