Background: Porcine reproductive and respiratory syndrome (PRRS) has been present in China for about 30 years, and because of the high mutability of PRRSV, it causes huge economic losses to pig enterprises every year. PRRSV-2 is widely prevalent in China, and the detection rate of PRRSV-1 is also on the rise. Nonstructural protein 2 (NSP2) is a highly variable protein with multiple biological functions, such as PRRSV replication, which plays an important role in understanding PRRSV variation and epidemic alerts. Objectives: The epidemic characteristics and recombination of PRRSV-1 NSP2 are still unknown. The purpose of this study is to study the epidemic characteristics of PRRSV-1 NSP2 and lay a foundation for the prevention and control of PRRSV-1. Methods: In this study, we collected several PRRSV-1 and PRRSV-2 NSP2 gene sequences for gene sequence and recombination analyses, aiming to analyze the recombination pattern and genetic variation in the PRRSV-1 NSP2 genes in China. Results: The genetic similarity results showed that the 69 PRRSV-1 NSP2 gene sequences collected in this study showed nucleotide similarity ranging from 67.3% to 100.0% and amino acid similarity ranging from 64.3% to 100.0%. Amino acid sequence comparison showed that PRRSV-1 had more amino acid deletion or substitution sites than PRRSV-2. NSP2 also contains special amino acid regions such as the highly immunogenic region. PRRSV-1 can be categorized into four strains, NMEU09-1-like, BJEU06-1-like, HKEU-16-like and Amervac-like isolates, and are at different positions in the ML and NJ phylogenetic trees. In the ninety selected PRRSVs, six recombination events were detected using recombination analysis, two of which occurred in Chinese PRRSV-1 strains. Therefore, sequence analysis of NSP2 helps us to understand the prevalence and variation in PRRSV-1 in China over the past two decades and provides a theoretical basis for studying the epidemiology and evolution of NSP2.

Porcine reproductive and respiratory syndrome virus (PRRSV) poses a significant threat to the global swine industry. In this study, the genetic diversity, evolutionary dynamics, and key antigenic characteristics of the PRRSV-1 GP5 gene in China were systematically investigated. A total of 114 Chinese PRRSV-1 GP5 sequences, isolated between 1999 and 2024, were analyzed alongside global reference strains. The nucleotide and amino acid sequence similarities ranged from 60.03% to 100% and from 48.72% to 100%, respectively, with mutation and deletion hotspots concentrated in the N-terminal hypervariable region. Phylogenetic analysis further classified the Chinese strains into four major lineages: Amervac-like, BJEU06-1-like, HKEU16-like, and NMEU09-1-like. Notably, a preliminary phylogenetic observation indicated that several recent Chinese PRRSV-1 isolates clustered topologically close to PRRSV-2 strains. However, as this finding is based solely on a single-gene tree and has not been validated by formal tests for convergent evolution, homoplasy, or selection pressure, it should be interpreted with caution and warrants further investigation using whole-genome data. A Bayesian evolutionary analysis estimated the evolutionary rate at 1.94 × 10⁻³ substitutions per site per year and the time to the most recent common ancestor at approximately 1910. No statistically significant recombination events were identified within the GP5 gene. The transmembrane topology of GP5 was highly conserved, whereas B-cell linear epitopes were enriched in the N-terminal extracellular region. This study establishes a useful molecular foundation for understanding PRRSV-1 evolution in China and offers valuable insights for the development of broad-spectrum vaccines and effective control strategies.

Background/Objectives: Porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2) remains the predominant genotype circulating in China and continues to evolve through mutation and recombination. Although NSP1 is recognized as a multifunctional nonstructural protein involved in immune regulation, its genetic variation among PRRSV-2 strains circulating in China has not been comprehensively characterized. Methods: In this study, 425 complete NSP1 sequences, primarily representing PRRSV-2 strains circulating in China, were analyzed, and 48 representative strains were selected for pairwise percent-identity visualization. Results: Pairwise nucleotide identity among the 48 representative strains was found to range from 80.1% to 100.0%, with the lowest value detected between AHBZ and SD-R, whereas pairwise amino-acid identity ranged from 79.6% to 100.0%, with the lowest value detected between AHBZ and HNhx. Among the 425 aligned amino-acid sequences, 290 variable sites and 93 completely conserved sites were identified. The broad-lineage distribution was composed of Lineage 1 (n = 79), Lineage 3 (n = 4), Lineage 5 (n = 21), and Lineage 8 (n = 321). A global FEL dN/dS of approximately 0.2979 was estimated from 379 non-recombinant unique haplotypes, and seven high-confidence candidate positively selected sites—42, 239, 255, 302, 367, 370, and 378—were supported by MEME, FEL, and FUBAR. A descriptive lineage-biased pattern concentrated in Lineage 5 was observed for NSP1β Val19Ile, corresponding to full-length NSP1 V199I. Eight candidate recombination events were identified using RDP4, and six representative events were further examined using SimPlot. Conclusions: Overall, NSP1 was found to be under predominant purifying selection while retaining localized variability, lineage-biased residue patterns, and candidate recombination signals that should be interpreted cautiously and validated experimentally.

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRSV, remains a major threat to the global swine industry, and current control relies mainly on vaccination. GP5a, encoded by ORF5a, is a newly identified non-glycosylated envelope structural protein of PRRSV. This review summarizes published studies on the discovery, molecular characteristics, genetic evolution, biological functions, and applications of GP5a, with emphasis on its sequence variation, interactions with host and viral proteins, roles in replication and virulence, and co-evolution with GP5. GP5a is approximately 5–6 kDa and is the smallest PRRSV structural protein. Although relatively conserved, it shows amino acid variations mainly in transmembrane and intramembrane domains. GP5a interacts with host proteins and viral nonstructural proteins, participates in replication and transcription, regulates virulence, and influences immune responses. Silencing GP5a markedly reduces viral titers, and GP5a mutations are associated with attenuation and virulence reversion. GP5a co-evolves with GP5 through overlapping ORF5a/ORF5 and codon usage balance. Its immunogenicity and conserved epitopes make it a potential target for vaccines, diagnostics, and antiviral drugs, although neutralizing antibodies induced by GP5a are limited. Its structure, interactome, and precise molecular mechanisms should be clarified in further studies.