Molecular analysis of Newcastle disease virus isolates reveals a novel XIId subgenotype in Vietnam.

Eight Vietnamese Newcastle disease virus field isolates from 2008-2015 and 3 vaccine specimens were genotyped based on their full F gene sequences and compared to 80 reference strains representing all 18 genotypes. Three isolates formed a novel subgenotype XIId, identified for the first time in Vietnam; while the others clustered as follows: four in subgenotypes VIId and VIIh; two in Genotype I; and two in Genotype II. Evolutionary distance calculations confirmed the Vietnamese XIId isolates were distinct from XIIa and XIIb by 0.062-0.070; and from other genotypes by 0.089-0.245. This data demonstrated that a novel XIId subgenotype emerged in Vietnam indicating considerable genetic diversity, thus highlighting the need to implement antigenic matching during vaccination against NDVs.