Sequencing and phylogenetic analysis reveal the prevalence of duck hepatitis a virus genotype-3 in vietnam

Duck hepatitis A virus (DHAV) causes an acute and highly contagious disease in young ducklings worldwide. Despite the widespread use of the DHAV vaccine, many outbreaks still occur in Vietnam. In this study, we determined the full-length genome sequence of two DHAV isolates (NC and NT) obtained from infected ducks in 2009 and 2013, and compared them with the attenuated DHAV-1 vaccine strain (namely, VXXT) currently used in Vietnam. The NC and NT strains belong to the virulent DHAV-3 genotype, and their genomes consist of 7791 and 7790 nucleotides (nt), respectively. Both genomes contain one large open reading frame (ORF) of 6756 nt, encoding a polyprotein of 2251 amino acids and possess a typical picornavirus genome organization. The majority of predicted C-terminal cleavage sites in the polyprotein were Q/S or Q/G. Phylogenetic analysis of the nucleotide sequence of the full ORF revealed that all virulent Vietnamese strains are closely related to Chinese DHAV-3 strains. Noticeably, the virulent Vietnamese DHAV-3 strains had relatively low nucleotide identity with the DHAV-1 vaccine strain (73.5%). The study showed that an antigenicity-matched DHAV-3 vaccine is urgently required for use in Vietnam.