Porcine reproductive and respiratory syndrome virus (PRRVS) is a major swine viral pathogen that affects the pig industry worldwide. Control of early PRRSV infection is essential, and different types of PRRSV-positive samples can reflect the time point of PRRSV infection. This study aims to investigate the epidemiological characteristics of PRRSV in China from Q4 2021 to Q4 2022, which will be beneficial for porcine reproductive and respiratory syndrome virus (PRRSV)control in the swine production industry in the future. A total of 7518 samples (of processing fluid, weaning serum, and oral fluid) were collected from 100 intensive pig farms in 21 provinces, which covered all five pig production regions in China, on a quarterly basis starting from the fourth quarter of 2021 and ending on the fourth quarter of 2022. Independent of sample type, 32.1% (2416/7518) of the total samples were PCR-positive for PRRSV, including 73.6% (1780/2416) samples that were positive for wild PRRSV, and the remaining were positive for PRRSV vaccine strains. On the basis of the time of infection, 58.9% suckling piglets (processing fluid) and 30.8% weaning piglets (weaning serum) showed PRRSV infection at an early stage (approximately 90% of the farms). The sequencing analysis results indicate a wide range of diverse PRRSV wild strains in China, with lineage 1 as the dominant strain. Our study clearly demonstrates the prevalence, infection stage, and diversity of PRRSV in China. This study provides useful data for the epidemiological understanding of PRRSV, which can contribute to the strategic and systematic prevention and control of PRRSV in China.

This study aimed to evaluate the effectiveness of combining load–close–homogenize (LCH), test and removal (T&R), and rollover strategies for PRRSV elimination in breeding herds using PRRSV-positive weaned gilts. Here, a novel strategy was explored for PRRSV elimination from more than 1500 weaned gilts, and we documented the process from PRRSV natural infection to elimination at the herd level. With LCH implementation, the herd achieved PRRSV-positive stability within 8 months. Consequently, by rolling in self-breeding PRRSV-naive gilts to replace PRRSV-positive weaned sows batch by batch, the time from being positive stable to negative was 13 months. A PRRSV-positive farm intending to retain its genes in its repopulate farrow to become a finished breeding farm can initiate PRRSV elimination from its weaned gilts; this will result in the first farrowing batch of piglets aged 8–10 weeks becoming PRRSV-negative after 8 months of herd closure. This approach offers a viable pathway for genetic retention and PRRSV elimination in breeding farms.

Porcine reproductive and respiratory syndrome virus (PRRSV) modified live virus (MLV) vaccination is used to control PRRSV. In China, farms conduct random sampling from sow herds every 4 to 6 months. They use the enzyme-linked immunosorbent assay (ELISA) method to monitor the immune status of the herd by tracking the positive rate or the sample-to-positive ratio. However, in farms that implement mass vaccination and have stable production, the positive rate of ELISA antibodies has decreased, especially in high-parity sows. This poses a considerable challenge to the current monitoring approach of PRRSV immunity. It remains unclear whether this reflects insufficient sensitivity of the kits for these special scenarios or the fact that the sows have truly lost immunity. In this study, 233 samples from four farms (A–D) across different regions of China were acquired. They were tested using four representative ELISA kits, two targeting the nucleocapsid protein (N) and two targeting the glycoprotein (GP) to evaluate PRRS immune status. The respective sample positive rates in A–D were 57.1–100%, 50.9–100%, 50–100%, and 75.7–100% using the kits. The positive rates using the four ELISA kits were 50.0–75.7%, 70.0–75.7%, 82.5–97.1%, and 100%, respectively, with poor agreement among them. The positive rates and humoral antibody levels for parity 1 and 2 sows were significantly lower than those with higher parities (>4). Eighty-eight ELISA-negative samples identified using ELISA kit A were verified using a viral neutralizing test (VNT), with only 15.9% of the samples testing negative. In conclusion, the ELISA antibody negativity issue existed, mostly occurring in specific farms tested using a specific kit. However, the low correlation with the VNT results and the poor agreements among the kits suggest that relying on one ELISA test is insufficient to monitor the immune status of PRRSV MLV-vaccinated herds.

Understanding how these viruses change is the starting point for rational control. Zhang et al. characterized the genetic diversity and pathogenicity of contemporary PRRSV-2 strains circulating in China. Their work highlights recombination as a major force shaping PRRSV diversity and shows why sequence data are most informative when interpreted alongside virological and pathogenicity findings. A newly detected strain matters not simply because it occupies a distinct position on a phylogenetic tree, but because of what it can do in the host: replicate, spread, evade immunity, and cause disease.At the molecular level, Zheng et al. reviewed the many functions of nonstructural protein 2 (NSP2), one of the most variable proteins in the PRRSV genome. NSP2 contributes to viral replication and interacts with host regulatory and immune pathways, while its extensive variability mirrors the broader evolutionary plasticity of PRRSV. Read together, these two contributions link populationlevel viral evolution with the molecular processes that support replication, adaptation, and immune evasion. They also underscore a point that is easy to overlook: genetic variation becomes meaningful only when its biological consequences are understood.As viruses evolve, surveillance must become more practical, more representative, and better suited to decisions made at herd level. Plut et al. evaluated oral fluid both as a non-invasive matrix for PRRS monitoring and as part of a controlled-exposure strategy during gilt acclimatization. Their findings show that oral fluid can provide a practical window into group-level infection dynamics, while also making clear that contaminated ropes alone are not a reliable substitute for effective exposure. This balance between promise and limitation is important. Diagnostic tools should be judged not only by analytical performance, but also by how they behave in the realities of commercial production.Turlewicz-Podbielska et al. extended the same field-oriented logic to PCV2 surveillance by evaluating testicular processing fluid for the detection of viral DNA and virus-specific antibodies. Because this material is already generated during routine procedures, it offers a way to gather herdlevel information without additional invasive sampling. The study also shows that matrix-specific cut-offs and careful attention to pooling are essential, particularly when low-level positives may otherwise be missed. Together, these two studies illustrate that innovation in diagnostics is not limited to inventing new assays; it also lies in making better use of specimens that farms already produce.Vaccination remains central to PRRSV and PCV control, but viral diversity means that vaccine performance must be revisited continually. Suh et al. assessed the reproductive protection conferred by a modified-live PRRSV vaccine against a heterologous Korean PRRSV-2 challenge in pregnant sows. Their study is especially valuable because reproductive disease is among the most damaging consequences of PRRS, and protection in breeding animals cannot be fully inferred from experiments in growing pigs. The observed improvements in reproductive outcome, virological measures, and cellular immune responses provide practical evidence for cross-protection in a biologically and economically relevant model. Liu et al. explored a different path by developing a baculovirus-engineered bivalent subunit vaccine candidate targeting the capsid antigens of PCV2 and PCV3. The study addresses an increasingly important need: broadening protection as more than one porcine circovirus contributes to field disease. The candidate induced humoral and cellular immune responses and reduced pathological damage following challenge, supporting further development. As with any new vaccine platform, field validation will be crucial, but the work offers a clear example of how antigen design can be adapted to an evolving epidemiological landscape.Taken together, the six articles present PRRSV and PCV control as a connected process rather than a collection of separate tasks. Genomic surveillance identifies emerging diversity; molecular studies help explain its biological significance; practical sampling strategies convert surveillance into herdlevel information; and vaccine studies test whether existing or newly designed tools remain fit for contemporary viruses. Progress in one area strengthens the others, and weaknesses in one can limit the whole system.