Phylogenotyping of infectious bursal disease virus in Vietnam according to the newly unified genotypic classification scheme

Since 1987, infectious bursal disease virus (IBDV) has circulated and evolved in Vietnam, but little is known about the genotypes present. IBDV samples were collected in 1987, 2001-2006, 2008, 2011, 2015-2019, and 2021 in 18 provinces. We conducted phylogenotyping analysis based on an alignment of 143 VP2-HVR (hypervariable region) sequences from 64 Vietnamese isolates (26 previous and 38 additional sequences and two vaccines, and alignment of 82 VP1 B-marker sequences, including one vaccine and four Vietnamese field strains. The analysis identified three A-genotypes, A1, A3, and A7, and two B-genotypes, B1 and B3, among the Vietnamese IBDV isolates. The lowest average evolutionary distance (8.6%) was seen between the A1 and A3 genotypes, and the highest (21.7%) was between A5 and A7, while there was a distance of 14% between B1 and B3 and 17% between B3 and B2. Unique signature residues were observed for genotypes A2, A3, A5, A6, and A8, which could be used for genotypic discrimination. A timeline statistical summary revealed that the A3-genotype predominated (79.8% presence) in Vietnam from 1987 to 2021 and that it remained the dominant IBDV genotype over the last five years (2016–2021). The current study contributes to a better understanding of the circulating genotypes and evolution of IBDV in Vietnam and worldwide.