ORF5-Based Molecular Characterization of PRRSV Reveals Multiple Co-circulating Lineages in Vietnam, 2021-2026.
Porcine reproductive and respiratory syndrome virus (PRRSV) continues to pose a major challenge to swine production in Vietnam because of its rapid evolution and genetic diversity. Here, we analyzed 69 PRRSV-positive samples collected from 20 provinces in Vietnam between 2021 and 2026 using ORF5 gene sequencing to characterize the genetic diversity of circulating strains. Phylogenetic analysis demonstrated the co-circulation of multiple PRRSV-2 lineages (L1, L3, L5, L8, and L10), together with a limited presence of PRRSV-1, indicating a genetically diverse PRRSV population within the analyzed diagnostic samples. Among the PRRSV-2 strains, lineage 8 (L8), particularly sub-lineage L8E, was the most frequently detected, whereas lineage 10 (L10) accounted for 24.6% of the sequenced isolates and was detected only in samples collected from 2023 onwards. Independent maximum-likelihood phylogenetic and pairwise ORF5 distance analyses showed that the Vietnamese L10 strains formed a distinct monophyletic cluster within lineage 10. Analysis of the GP5 protein identified amino acid variation in previously described antigenic regions, providing descriptive information on the genetic diversity of circulating Vietnamese PRRSV strains. Collectively, these findings provide updated insights into the molecular epidemiology of PRRSV in Vietnam and highlight the value of continuous molecular surveillance for monitoring the emergence and distribution of PRRSV lineages.