Recent Progress in Studies of Porcine Reproductive and Respiratory Syndrome Virus 1 in China

Single-B-cell cloning and recombinant antibodies generation to analyze the antigenicity of porcine reproductive and respiratory syndrome virus nonstructural protein 12

The prevalence and variation of porcine reproductive and respiratory syndrome virus (PRRSV) in China are increasing. The rapid preparation of essential antibodies will effectively reveal the antigenicity, epitopes, and intracellular distribution of viral proteins. Single-B-cell antibody technology is a novel method for screening diverse functional monoclonal antibodies (mAbs). Herein, we successfully expressed PRRSV nonstructural protein 12 (Nsp12) in suspension-cultured Chinese hamster ovary (CHO) cells. Using single-B-cell antibody technology, we utilized fluorescence-activated cell sorting to collect individual immune B cells and prepared single-cell reverse transcription-polymerase chain reaction to clone the variable region of immunoglobulin heavy chain (IgH) and immunoglobulin light chain (IgK). Two recombinant mAbs were generated via transient transfection of CHO cells with the corresponding expression plasmids of IgH and IgK. A novel linear epitope (104YEFTGNGEDW113) of Nsp12 was identified using mAb1N14. This epitope was conserved in lineages 1, 5, and 8 of PRRSV-2 and was located on the surface of the Nsp12 spatial structure. The amino acid mutation in Nsp12 of lineage 3 PRRSV-2 affected the antigenicity of this linear epitope. A conserved conformational epitope was identified using mAb2S18, and the spatial structure of Nsp12 showed high similarity between PRRSV-1 and different lineages of PRRSV-2. During PRRSV infection, Nsp12 was distributed in the cytoplasm and accumulated in the nucleus. Overall, antigenicity analysis and novel epitope identification contributed to the in-depth exploration of the biological function of Nsp12 and will facilitate the development of detection assays and antiviral strategies.

Porcine reproductive and respiratory syndrome virus nsp5 inhibits the activation of the Nrf2/HO-1 pathway by targeting p62 to antagonize its antiviral activity

Porcine reproductive and respiratory syndrome virus (PRRSV) infections often trigger oxidative stress and cytokine storms, resulting in significant tissue damage that causes fatalities in piglets and reproductive issues in sows. However, it is still unknown how oxidative stress is regulated by viral and host factors in response to PRRSV infection. Here, we found that PRRSV induced cellular oxidative stress by triggering the production of reactive oxygen species and inhibiting the expression of antioxidant enzymes. Although Nrf2 is an important redox regulator that initiates the expression of downstream antioxidant genes, PRRSV can impair the Nrf2/HO-1 pathway. The overexpression of Nrf2 showed a significant anti-PRRSV effect, and inhibiting the expression of Nrf2 promoted the proliferation of PRRSV. Further analysis showed that Nrf2 positively regulated the production of type I interferons and interferon-stimulated genes, which may contribute to its anti-PRRSV effect. By screening the PRRSV-encoded protein, we found that the PRRSV nsp5 protein can degrade Nrf2 at the protein level. Mechanistically, nsp5 promotes Nrf2-Keap1 binding affinity by inhibiting p62-mediated Keap1 sequestration and increasing Keap1 expression. Subsequently, this increased Keap1-mediated degradation of Nrf2 ubiquitination through K48-linked polyubiquitin. Furthermore, we found that the residues Tyr146 and Arg147 of nsp5 are crucial for inhibiting the activation of the p62-mediated Nrf2 antioxidant pathway. Thus, our findings uncover a novel mechanism by which PRRSV disrupts the host antioxidant defense system and highlight the crucial role of the Nrf2/HO-1 antioxidant pathway in host defense against PRRSV.IMPORTANCEOxidative stress-induced redox imbalance is a crucial pathogenic mechanism in viral infections. Nrf2 and its antioxidant genes serve as the main defense pathways against oxidative stress. However, the role of Nrf2 in the context of porcine reproductive and respiratory syndrome virus (PRRSV) infection remains unclear. In this study, we demonstrated that PRRSV infection decreased the expression of antioxidant genes of the Nrf2 signaling pathway and overexpression of Nrf2 triggered a strong anti-PRRSV effect. PRRSV nsp5 enhanced Keap1-dependent degradation of Nrf2 ubiquitination, thereby weakening cellular resistance to oxidative stress and antagonizing the antiviral activity of Nrf2. Our study further revealed a new mechanism by which PRRSV evades host antiviral innate immunity by disturbing cellular redox homeostasis, providing a new target for developing anti-PRRSV drugs.

Emergence, prevalence and evolution of porcine reproductive and respiratory syndrome virus 1 in China from 1994 to 2024

Porcine reproductive and respiratory syndrome virus 1 (PRRSV-1) was first detected in Chinese swine herds during an epidemiological investigation since 1994. Even though PRRSV-1 has been existed in China for 30 years, much less attention was paid on PRRSV-1 than PRRSV-2. This review systematically evaluated the emergence, prevalence and evolution of Chinese PRRSV-1 from 1994 to 2024. Here we showed that PRRSV-1 has been detected in at least 28 regions of China, which can be divided into eight subgroups within subtype 1. During the evolution in Chinese swine herds, a large number of substitutions, insertions and deletions were identified. Recombination events were also commonly detected accompanying with nsp1-nsp3, nsp9-nsp10 and ORF2-ORF6 regions as the cross-over hotspots. Remarkably, Chinese PRRSV-1 isolates showed a trend of increasing in pathogenicity in recent years. At last, we discussed the differential detection methods and cross-protection strategies against PRRSV-1 isolates. Overall, PRRSV-1 has become one of the widely-spread viruses in China posing a significant threat to China's swine industry.

Development of a triplex crystal digital PCR for the detection of PRCoV, PRRSV, and SIV

Porcine respiratory coronavirus (PRCoV), porcine reproductive and respiratory syndrome virus (PRRSV), and swine influenza virus (SIV) are important pathogens of significant infectious diseases. They cause similar clinical respiratory symptoms, including fever, cough, runny nose, and respiratory distress, which makes these diseases difficult to distinguish from each other. In this study, three pairs of specific primers and TaqMan probes were designed for the conserved regions of the PRCoV S gene, PRRSV N gene, and SIV M gene, respectively. The annealing temperature, primer and probe concentrations, and reaction cycle were optimized, and a triplex crystal digital PCR (cdPCR) assay was established for the detection of PRCoV, PRRSV, and SIV. According to the test results, the assay was capable of specifically detecting PRCoV, PRRSV, and SIV, and there was no cross-reaction with other control swine viruses. Based on the Poisson distribution analysis, the limits of detection (LODs) for PRCoV, PRRSV, and SIV were 6.00, 5.75 and 6.00 copies/reaction, respectively, and the sensitivity was 26 times higher than those of the corresponding multiplex RT-qPCR. The coefficients of variation (CVs) of the intra-assay and inter-assay ranged from 0.19 to 1.84%. The assay was used to test 1,657 clinical samples, and the positivity rates of PRCoV, PRRSV, and SIV were 1.15, 12.79, and 2.05%, respectively. It showed diagnostic sensitivity and specificity of 100 and 99.82% for PRCoV, 100 and 99.24% for PRRSV, and 100 and 99.69% for SIV, respectively. These results indicated that the triplex cdPCR assay has strong specificity, high sensitivity, and excellent repeatability, which provides a valuable tool for the detection and differentiation of PRCoV, PRRSV, and SIV.

A nucleocapsid monoclonal antibody based sandwich ELISA for the general detection of both PRRSV-2 and PRRSV-1

Porcine reproductive and respiratory syndrome virus (PRRSV) causes reproductive failure in sows and respiratory disease in growing pigs, leading to significant economic losses worldwide. Due to the constant mutation and recombination, PRRSV exhibits significant genetic diversity, the general detection of all PRRSV-2 and PRRSV-1 strains is thus needed. In our study, four monoclonal antibodies (mAbs) against PRRSV nucleocapsid (N) protein were generated and the precise and novel B cell epitopes (52KPHF55 and 109HHTVR113) were identified. The epitope 52KPHF55 is highly conserved across all strains of PRRSV-2 lineages and PRRSV-1 subtypes, and the corresponding two mAbs (6D7, 4D12) were selected to develop a sandwich ELISA that was able to detect all tested PRRSV-2 and PRRSV-1 strains. The developed sandwich ELISA demonstrated high specificity, sensitivity and repeatability. In detection of 133 clinical samples, the sandwich ELISA achieved 84.21 % coincidence with the real-time RT-PCR. In conclusion, the mAb based sandwich ELISA can be suitable for detection of potential all PRRSV-2 lineages and PRRSV-1 subtypes, providing a simple, quick and high content method for diagnosis of PRRS.

Porcine Reproductive and Respiratory Syndrome Virus: Challenges and Advances in Vaccine Development

Persistent infection of porcine reproductive and respiratory syndrome virus (PRRSV) significantly hampers both the quantity and quality of pork production in China. Although PRRSV is widely prevalent worldwide, the absence of effective vaccines has made it one of the major pathogens threatening the sustainable development of the global swine industry. Vaccination remains one of the most effective measures for controlling pathogen infections. However, the continuous genetic recombination and mutation of PRRSV demand more comprehensive strategies to address emerging threats, while ensuring the efficacy and safety of vaccines. This review provides an overview of the latest advances in PRRSV vaccine research, highlighting the importance of understanding the unique strengths and limitations of various vaccines in developing effective therapeutic approaches and vaccination strategies. Moreover, the development of adjuvants and antiviral drugs as adjuncts to combat PRRSV infection offers significant potential for enhancing disease control efforts. With the advancement of technologies such as proteolysis-targeting chimera (PROTAC) and mRNA, new avenues for controlling PRRSV and other pathogens are emerging, offering considerable hope. Ultimately, the goal of these vaccine developments is to alleviate the impact of PRRSV on animal health and the profitability of the swine industry.

Engineering a live-attenuated porcine reproductive and respiratory syndrome virus vaccine to prevent RNA recombination by rewiring transcriptional regulatory sequences

Recombination is a significant factor driving the evolution of RNA viruses. The prevalence and variation of porcine reproductive and respiratory syndrome virus (PRRSV) in China have been increasing in complexity due to extensive interlineage recombination. When this recombination phenomenon occurs in live vaccine strains, it becomes increasingly difficult to prevent and control PRRSV. Reverse genetic manipulation to engineer a different transcriptional regulatory sequence (TRS) circuit introduces genetic traps into the viral genome that are lethal to recombinant RNA progeny viruses. In this study, major interlineage recombination patterns were identified between lineage 1 (L1) PRRSVs and lineage 8 (L8) PRRSVs in China, from 2019 to 2023. The recombinant mutant virus, vA-TRSall, was constructed and successfully rescued by rewiring the entire TRS circuit without changing the amino acid-coding sequence in the genome of the PRRSV live vaccine strain vHuN4-F112. The vA-TRSall, with a brand new TRS circuit, provided effective immune protection against the highly pathogenic L8 PRRSV (vHuN4) and epidemic NADC30-like L1 PRRSV (vZJqz21). Recombination analysis in vitro and in vivo showed that, compared with the vHuN4-F112 and vZJqz21 co-infection groups, the incidence rates of mutation breakpoints and template-switching recombination in the vA-TRSall and vZJqz21 co-infected groups were effectively reduced. The results have enriched our understanding of the critical role of TRS circuits in PRRSV recombination mechanisms and indicate a successful redesign that can endow PRRSV live vaccines with recombination-resistant capabilities.

IMPORTANCE

Porcine reproductive and respiratory syndrome viruses (PRRSVs) are genetically diverse, and this is due in part to their extensive recombination. Live vaccines are widely used to prevent and control PRRS in China. However, owing to the wide variety of live vaccines, non-standard use, and the wild viruses prevalent on pig farms, new strains, generated via RNA recombination, are continuously emerging. Vaccine strains are also involved in PRRSV recombination, which leads to the emergence of new variants and alterations in virulence and pathogenesis. A recombination-resistant genome was engineered by rewiring the entire transcriptional regulatory sequence (TRS) circuit of the live PRRSV vaccine strain. Theoretically, after clinical application, once the virus recombines with the genome of the epidemic strain, the base pairing between the two sets of TRS circuits should be disrupted, resulting in a fatal genetic trap for the generation of an RNA recombinant progeny virus. Therefore, the remodeled PRRSV TRS mutant generated in this study can serve as a recombination-resistant platform for the rational design of safe PRRS vaccines in the future.

The neonatal Fc receptor (FcRn) is required for porcine reproductive and respiratory syndrome virus uncoating

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause substantial economic losses to the pig industry worldwide. Previous studies from other groups showed that CD163 is required for PRRSV uncoating and genome release. However, CD163 does not interact with nucleocapsid (N) protein. In this study, the neonatal Fc receptor (FcRn) was demonstrated to be irreplaceable for PRRSV infection by knockdown, overexpression, antibodies or IgG blocking, knockout, and replenishment assays. FcRn was further revealed to be involved in PRRSV uncoating for the first time rather than viral attachment and internalization. In detail, FcRn was determined to colocalize with CD163 and PRRSV virions in early endosomes and specially interact with N protein in early endosomes. Taken together, these results provide evidence that FcRn is an essential cellular factor for PRRSV uncoating, which will be a promising target to interfere with the viral infection.IMPORTANCEPRRSV infection results in a severe swine disease affecting pig farming in the world. Although CD163 has been implicated as the uncoating receptor for PRRSV but the uncoating mechanism of PRRSV remains unclear. Here, we identified that FcRn facilitated virion uncoating via interaction with viral N protein in early endosomes. Our work actually expands the knowledge of PRRSV infection and provides an attractive therapeutic target for the prevention and control of PRRS.

Lineage 7 Porcine Reproductive and Respiratory Syndrome Vaccine Demonstrates Cross-Protection Against Lineage 1 and Lineage 3 Strains

Background/Objectives: Porcine reproductive and respiratory syndrome virus (PRRSV) has a major impact on swine productivity. Modified-live vaccines (MLVs) are used to aid in control. We investigated the cross-protection provided by a lineage 7 PRRSV MLV against a lineage 1 isolate under laboratory conditions and a lineage 3 challenge under field conditions in Taiwan. Methods: In the first study, thirty PRRS antibody-negative conventional piglets were vaccinated via the intramuscular (IM) or the intradermal (ID) route, with the control group receiving a placebo. Four weeks after immunization, all groups were challenged with a Taiwanese lineage 1 strain. The standard protocol for detection of reversion to virulence was applied to the vaccine strain in the second study, using sixteen specific pathogen-free piglets. In the third study, on an infected pig farm in Taiwan (lineage 3 strain), three hundred piglets were randomly selected and divided into three groups, each injected with either the PrimePac® PRRS vaccine via the IM or the ID route, or a placebo. Results: In the first study, both vaccinated groups demonstrated reduced viraemia compared to the control group. The second study demonstrated that the MLV strain was stable. In the third study, piglet mortality, average daily weight gain, and pig stunting rate were significantly improved in the vaccinated groups compared to the control group. Conclusions: PrimePac® PRRS is safe to use in the field in the face of a heterologous challenge, successfully providing cross-protection against contemporary lineage 1 and lineage 3 PRRSV strains from Taiwan.

Isolation and Genomic Characterization of a Novel Porcine Reproductive and Respiratory Syndrome Virus 1 from Severely Diseased Piglets in China in 2024

Since the first isolation of the porcine reproductive and respiratory syndrome virus 1 (PRRSV-1) BJEU06-1 strain from a Beijing pig farm in 2006, more and more PRRSV-1 isolates have been identified in China. In this study, we performed the routine detection of PRRSV-1 using 1521 clinical samples collected in 12 provinces/cities from February 2022 to May 2024. Only three lung samples from severely diseased piglets collected in January 2024 were detected as PRRSV-1-positive (0.197%, 3/1521). A PRRSV-1 strain (AHEU2024-2671) was successfully isolated in primary alveolar macrophages (PAMs) but not in Marc-145 cells. Genome sequencing showed that the AHEU2024-2671 isolate shared the highest genome similarity (90.67%) with the SC2020-1 isolate but only 84.01% similarity with the predominant BJEU06-1 strain. Noticeably, the AHEU2024-2671-like isolates not only contained deletions in nsp2 and the GP3-GP4 overlap region, but also contained a unique 6 nt deletion between nsp12 and the ORF2 gene. Furthermore, a genome-based phylogenetic tree supported that the AHEU2024-2671-like isolates form a novel subgroup within subtype 1. Overall, this study not only supported the idea that PRRSV-1 is rapidly evolving in Chinese swine herds, but also pulled the alarm that novel PRRSV-1 isolates with potentially increased pathogenicity might already exist in China, although they are still rarely detected among Chinese pigs.

A Simple and Sensitive RT-qPCR Technology for Rapid Detection of Porcine Reproductive and Respiratory Syndrome Virus

To establish a rapid and sensitive detection method for the porcine reproductive and respiratory syndrome virus (PRRSV), gene-specific primers and a TaqMan probe were designed based on the M gene of PRRSV, and a new stable fully pre-mixed reverse transcription real-time fluorescence quantitative PCR (RT-qPCR) reaction mixture was developed. A simple and rapid RT-qPCR detection method for PRRSV was developed by optimizing nucleic acid amplification conditions. The results showed that the method was able to specifically detect PRRSV without cross-reactivity with the other 11 porcine susceptible viruses. The sensitivities of the assay were 3.12 × 100 copies/μL and 100 TCID50/μL for M gene and virus, respectively, and the repeatability and reproducibility (relative standard deviation, CV) of the assay were less than 2.5%. Based on the new fullly pre-mixed RT-qPCR reaction mixture, the RT-qPCR detection method may provide a new, simple, and rapid method for accurately detecting PRRSV.

A Quadruplex RT-qPCR for the Detection of African Swine Fever Virus, Classical Swine Fever Virus, Porcine Reproductive and Respiratory Syndrome Virus, and Porcine Pseudorabies Virus

African swine fever virus (ASFV), classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), and porcine pseudorabies virus (PRV) induce similar clinical signs in infected pigs, including hyperthermia, anorexia, hemorrhage, respiratory distress, neurological symptoms, and/or abortions in pregnant sows. The differential diagnosis of these diseases relies on laboratory examinations. In this study, a quadruplex RT-qPCR was established using four pairs of specific primers and probes aimed at the B646L (p72) gene of ASFV, the 5' untranslated region (5'UTR) of CSFV, the ORF6 gene of PRRSV, and the gB gene of PRV for the detection and differentiation of ASFV, CSFV, PRRSV, and PRV. The assay exhibited great sensitivity with limits of detection (LODs) of 134.585, 139.831, 147.076, and 142.331 copies/reaction for ASFV, CSFV, PRRSV, and PRV, respectively. The assay exclusively identified ASFV, CSFV, PRRSV, and PRV, yielding negative results for the other control swine viruses used in this study. The intra-assay and inter-assay coefficients of variation (CVs) were not higher than 1.12%, indicating good reproducibility of the assay. The quadruplex RT-qPCR assay was used to analyze 3116 clinical tissue samples from pigs in Guangxi province, China, from April 2023 to September 2024. ASFV, CSFV, PRRSV, and PRV had positivity rates of 10.84% (338/3116), 0.80% (25/3116), 14.92% (465/3116), and 1.38% (43/3116), respectively, demonstrating a coincidence rate of ≥99.45% with the previously described RT-qPCR assays, which were also used to test these same samples. The established assay was rapid, sensitive, and accurate in detecting and differentiating ASFV, CSFV, PRRSV, and PRV.

Development of a Multiplex RT-qPCR Method for the Identification and Lineage Typing of Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen that causes porcine reproductive and respiratory syndrome (PRRS), leading to abortion of sows and the manifestation of respiratory diseases in piglets. PRRSV strains are categorized into two distinct genotypes: PRRSV-1 and PRRSV-2. PRRSV-2 can be further classified into several lineages, including sub-lineage 1.8 (NADC30-like), sub-lineage 1.5 (NADC34-like), lineage 8 (HP-PRRSV-like), lineage 5 (VR-2332-like), and lineage 3 (QYYZ-like), all of which are prevalent in China. In order to identify PRRSV-1 and PRRSV-2, two primer-probe combinations were designed, targeting the M gene. In order to further differentiate the five lineages of PRRSV-2, another five primer-probe combinations were designed, targeting the Nsp2 gene. A TaqMan-based multiplex RT-qPCR assay was subsequently developed, integrating the aforementioned seven sets into two primer pools. Following the optimization of primer concentration and annealing temperature, a comprehensive evaluation was conducted to assess the assay's amplification efficiency, specificity, repeatability, and sensitivity. The developed multiplex RT-qPCR method exhibited excellent repeatability, with coefficients of variation (CVs) less than 2.12%. The detection limits for all seven targets were found to be less than 5 copies/μL. Ultimately, the method was utilized for the detection of a total of 1009 clinical samples, with a PRRSV-positive rate of 7.63% (77/1009). Specifically, the reference method was utilized to further confirm the status of the 77 PRRSV-positive samples and another 27 samples suspected of PRRSV infection. The sensitivity of the method was 97.40% (75/77), and the specificity was 96.30% (26/27), resulting in an overall coincidence rate of 97.12% (101/104). All the PRRSV-positive samples were typed as NADC30-like strains, and the accuracy of this typing was further confirmed by Sanger sequencing. In conclusion, A one-step multiplex RT-qPCR method was successfully constructed, evaluated, and applied to detect clinical samples. The assay provides an easy-to-operate, time-saving, and highly efficient way for the quick identification of PRRSV and simultaneous detection of five PRRSV-2 lineages prevalent in China. The method could offer guidance for PRRSV prevention and control measures.

Identification of new antigenic epitopes of porcine reproductive and respiratory syndrome virus nsp12 protein using monoclonal antibodies

Porcine reproductive and respiratory syndrome virus (PRRSV), a member of the arteritis virus family, significantly impacts the swine industry due to its high infectiousness. nsp12, the nonstructural protein encoded by PRRSV, is a membrane-associated protein, with limited knowledge about its antigenic properties and functions. In this study, we used the expressed and purified nsp12 protein as antigen to immunize mice, and successfully screened five positive hybridoma cell lines that stably secrete anti-nsp12 monoclonal antibodies using immunological assays such as indirect ELISA and IFA. The antigenic epitopes recognized by the five monoclonal antibodies were identified using the fusion expression of peptides derived from the overlapping truncators of the nsp12 gene. The results showed that monoclonal antibodies 3G11 and 9C2 recognized the antigenic epitope 93TWGFESDTAY102, 2E3 recognized 115DYNDAFRARQ124, and 10G6 and 2A4 recognized 142PGPVIEPTL150. Furthermore, the three newly identified antigenic epitopes were all immunodominant and located on the surface of nsp12 protein. Notably, the antigenic epitopes 93-102 aa are all highly conserved across PRRSV-2 strains, making them suitable targets for PRRSV-2 detection. In conclusion, our findings advance the understanding of the antigenic properties of the PRRSV nsp12 protein and facilitate the development of assays for PRRSV detection.

Prevalence and genetic diversity of PRRSV in Sichuan province of China from 2021 to 2023: Evidence of an ongoing epidemic transition

Porcine reproductive and respiratory syndrome (PRRS) significantly impacts the global swine industry. Sichuan province, a key pig breeding center in China, has limited data on the molecular epidemiology of PRRS Virus (PRRSV). To address this, 1618 suspected PRRSV samples were collected from 2021 to 2023, with a prevalence rate of 39.74% (643/1618). Phylogenetic analysis showed PRRSV-2 as dominant (95.65%, 615/643), with PRRSV-1 at 4.35% (28/643). PRRSV-2 strains were further classified into NADC30-like (74.18%), NADC34-like (11.98%), C-PRRSV (5.44%), and HP-PRRSV (4.04%). The significant change in the proportions of different lineages indicates genomic divergence. NADC30-like strains exhibited significant amino acid mutations in ORF5, aiding immune evasion. Recombination analysis revealed complex patterns, primarily involving NADC30-like strains. This study highlights the genomic divergence of PRRSV in Sichuan, with NADC30-like strains becoming predominant and emerging strains like NADC34-like showing potential for further spread.

The evolution and diversity of porcine reproductive and respiratory syndrome virus in China

The porcine reproductive and respiratory syndrome virus (PRRSV) has emerged as a significant pathogen in the global pork industry since the late 1980s, causing substantial economic losses due to its high contagiousness and genetic variability. China, with its complex epidemiological landscape, has witnessed the emergence of four distinct lineages of PRRSV-2 (Lineages 1, 3, 5, and 8) and occasional occurrences of PRRSV-1. This review summarizes the historical context and epidemiological trends that have led to the diversification of PRRSV in China, discusses the evolutionary dynamics behind the establishment of diverse genetic variants, as well as the impact of recombination and modified live vaccines (MLVs) on the virus's rapid evolution. The implications for disease management, including strategies to reduce the complexity of PRRSV epidemics and improve prevention and control measures, are also suggested. Understanding the evolutionary pattern and factors contributing to PRRSV diversity is crucial for enhancing our knowledge, control capabilities, and prevention strategies, which could be integrated into swine health management practices.

Effects of herd closure and medication programs on the infection of NADC30-like PRRSV in pig farms

IMPORTANCE

The porcine reproductive and respiratory syndrome virus (PRRSV) poses a significant threat to swine production, particularly with emerging strains such as the highly virulent NADC30-like strain.

OBJECTIVE

This study examined the impact of PRRSV NADC30-like strains on pig farms in Fujian, China.

METHODS

The effectiveness of strategic management protocols, including herd closure, medication programs, monitoring of processing fluids (pig testicular fluid), and collection of production data, were analyzed. The prevalent strain in the pig farm was identified as a NADC30-like strain of the PRRSV through genetic sequencing comparison analysis.

RESULTS

The quantitative real-time reverse-transcription polymerase chain reaction results showed that the PRRSV cycle threshold (Ct) values of the processing fluid samples were relatively low from September to early October 2021. After implementing the intervention measures (October 2021), the Ct value increased gradually and reached a negative in March 2022, lasting six months. In addition, the average survival rate of the pigs before the intervention was 84.1%, while the average survival rate after the intervention was 93.1%.

CONCLUSIONS AND RELEVANCE

The use of 12-month intervals for pig herd closure, drug planning, and other strategic management agreements (multi-point production and active monitoring of production data, McREBEL) helped stabilize the subsequent pig farm production, providing a basis for clinical disease prevention and control.

Isolation and identification, genome-wide analysis and pathogenicity study of a novel PRRSV-1 in southern China

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused severe economic losses to the global swine industry. In recent years, the incidence of PRRSV-1 has been gradually increasing in China, but there are still few studies on it. In this study, clinical samples for PRRS virus isolation were collected from a pig farm in South China in 2022. We effectively isolated a strain of PRRSV utilizing PAM cells and demonstrated its consistent transmission capability on Marc-145 cells. The isolated strain was confirmed as PRRSV-1 by RT-qPCR, IFA, electron microscopy, etiolated spot purification and whole genome sequencing, the strain was named GD2022. The length of GD2022 genome is 15058nt; Based on the genome-wide genetic evolutionary analysis of GD2022, the strain was classified as PRRSV-1. Further genetic evolutionary analysis of its ORF5 gene showed that GD2022 belonged to PRRSV-1 subtype 1 and formed an independent branch in the evolutionary tree. Compared with the sequence of the classical PRRSV-1 strain (LV strain), GD2022 has several amino acid site mutations in the antigenic region from GP3 to GP5, these mutations are different from those of other PRRSV-1 strains in China. Recombination analysis showed no recombination events with GD2022. In addition, piglets infected with GD2022 displayed clinical respiratory symptoms and typical pathological changes. In this study, a strain of the PRRSV-1 virus was isolated using both PAM cells and Marc-145 and proved to be pathogenic to piglets, providing an important reference for the identification, prevention, and control of PRRSV-1.

Porcine reproductive and respiratory syndrome developments: An in-depth review of recent findings

The porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) belonging to the Arteriviridae family is the cause of PRRS disease. After being discovered for the first time in the United States in 1987, this illness quickly expanded to Canada. The disease was initially discovered in late 1990 in Germany, from where it quickly spread throughout Europe. The consequences of PRRSV lead to a number of epidemiological issues, including a sickness with a delayed immune response that permits extended viremia, which facilitates viral transmission. The virus penetrates the nasal epithelium, tonsils, lung macrophages, and uterine endometrium through the oronasal and genital pathways. Abortions performed late in pregnancy and premature or delayed deliveries resulting in dead and mummified fetuses, stillborn pigs, and weakly born piglets are indicative of reproductive syndrome. In the meanwhile, dyspnea, fever, anorexia, and lethargic behavior are signs of respiratory syndrome. The virus can be isolated from the tissue or serum of animals that have been infected to confirm the diagnosis. Pig movements and potential airborne dissemination are two ways that the virus can enter new herds and propagate through nose-to-nose contact or aerosols. Various supportive therapies may enhance infant survival, and antibiotics may or may not lessen the impact of secondary bacterial infections. The absence of simple diagnostic tests, the virus's airborne transmission, the occurrence of subclinical infections, and the virus's persistence in infected populations have all contributed to the failure of control efforts for PRRS.

Molecular mechanism of autophagy in porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome virus (PRRSV), a significant pathogen affecting the swine industry globally, has been shown to manipulate host cell processes, including autophagy, to facilitate its replication and survival within the host. Autophagy, an intracellular degradation process crucial for maintaining cellular homeostasis, can be hijacked by viruses for their own benefit. During PRRSV infection, autophagy plays a complex role, both as a defense mechanism of the host and as a tool exploited by the virus. This review explores the current understanding of the molecular mechanisms underlying autophagy induction under PRRSV infection, its impact on virus replication, and the potential implications for viral pathogenesis and antiviral strategies. By synthesizing the latest research findings, this article aims to enhance our understanding of the intricate relationship between autophagy and PRRSV, paving the way for novel therapeutic approaches against this swine pathogen.

Lineage 1 PRRSVs infection induces hemorrhagic injury in intestines of piglets: Effects on complement and coagulation cascades

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly transmissible disease of significant concern in the pig industry. Previous studies have demonstrated that the XM-2020 strain (a lineage 1.8 PRRSV IA/2012/NADC30) can induce special hemorrhagic injury in the small intestines. However, the specific mechanism underlying this injurious effect remains incompletely understood. In this study, we examined the pathogenic properties of XM-2020 and YC-2020 strains (a lineage 1.5 PRRSV IA/2014/NADC34) in piglets. Animal pathogenic tests revealed that with either Lineage 1 PRRSVs strains XM-2020 or YC-2020 demonstrated pronounced intestinal hemorrhage and suppression of peripheral immunological organs, comparing to JXA1 infection. Transcriptome analysis of diseased small intestines unveiled that PRRSV infection stimulated oxidative and inflammatory reactions. Remarkably, we also observed activation of the complement system alongside a notable down-regulation of complement and coagulation cascade pathways in the Lineage 1 PRRSVs infection group. Based on these findings, we propose that the primary mechanism driving the hemorrhagic injury of the small intestine caused by Lineage 1 PRRSVs is the suppression of complement and coagulation cascades resulting from immunosuppression. This discovery deepens our understanding of the pathogenicity of PRRSV in the small intestine and provides promising ways out for the development of innovative strategies aimed at controlling PRRSV.

Genetic Characterization and Pathogenicity of a Recombinant Porcine Reproductive and Respiratory Syndrome Virus Strain in China

Since it was first reported in 2013, the NADC30-like PRRSV has been epidemic in China. Hubei Province is known as China's key hog-exporting region. To understand the prevalence and genetic variation of PRRSV, herein, we detected and analyzed 317 lung tissue samples from pigs with respiratory disease in Hubei Province, and demonstrated that the NADC30-like strain was the second-most predominant strain during 2017-2018, following the highly pathogenic PRRSV (HP-PRRSV). Additionally, we isolated a new NADC30-like PRRSV strain, named CHN-HB-2018, which could be stably passaged in Marc-145 cells. Genetic characterization analysis showed that compared with the NADC30 strain, the CHN-HB-2018 strain had several amino acid variations in glycoprotein (GP) 3, GP5, and nonstructural protein 2 (NSP2). Moreover, the CHN-HB-2018 strain showed a unique 5-amino acid (aa) deletion in NSP2, which has not previously been reported. Gene recombination analysis identified the CHN-HB-2018 strain as a potentially recombinant PRRSV of the NADC30-like strain and HP-PRRSV. Animal experiments indicated that the CHN-HB-2018 strain has a mild pathogenicity, with no mortality and only mild fever observed in piglets. This study contributes to defining the evolutionary characteristics of PRRSV and its molecular epidemiology in Hubei Province, and provides a potential candidate strain for PRRSV vaccine development.

Synthetic Peptides Elicit Humoral Response against Porcine Reproductive and Respiratory Syndrome Virus in Swine

The aim of this study was to analyze the immunogenic response elicited in swine by two synthetic peptides derived from GP5 to understand the role of lineal B epitopes in the humoral and B-cell-mediated response against the porcine reproductive and respiratory syndrome virus (PRRSV). For inoculation, twenty-one-day-old pigs were allocated into six groups: control, vehicle, vaccinated (Ingelvac-PRRSV, MLV®), non-vaccinated and naturally infected, GP5-B and GP5-B3. At 2 days post-immunization (dpi), the GP5-B3 peptide increased the serum concentrations of cytokines associated with activate adaptive cellular immunity, IL-1β (1.15 ± 1.15 to 10.17 ± 0.94 pg/mL) and IL-12 (323.8 ± 23.3 to 778.5 ± 58.11 pg/mL), compared to the control group. The concentration of IgGs anti-GP5-B increased in both cases at 21 and 42 dpi compared to that at 0 days (128.3 ± 8.34 ng/mL to 231.9 ± 17.82 and 331 ± 14.86 ng/mL), while IgGs anti-GP5-B3 increased at 21 dpi (105.1 ± 19.06 to 178 ± 15.09 ng/mL) and remained at the same level until 42 dpi. Also, antibody-forming/Plasma B cells (CD2+/CD21-) increased in both cases (9.85 ± 0.7% to 13.67 ± 0.44 for GP5-B and 15.72 ± 1.27% for GP5-B3). Furthermore, primed B cells (CD2-/CD21+) from immunized pigs showed an increase in both cases (9.62 ± 1.5% to 24.51 ± 1.3 for GP5-B and 34 ± 2.39% for GP5-B3) at 42 dpi. Conversely the naïve B cells from immunized pigs decreased compared with the control group (8.84 ± 0.63% to 6.25 ± 0.66 for GP5-B and 5.78 ± 0.48% for GP5-B3). Importantly, both GP5-B and GP5-B3 peptides exhibited immunoreactivity against serum antibodies from the vaccinated group, as well as the non-vaccinated and naturally infected group. In conclusion, GP5-B and GP5-B3 peptides elicited immunogenicity mediated by antigen-specific IgGs and B cell activation.

Current Status of Vaccines for Porcine Reproductive and Respiratory Syndrome: Interferon Response, Immunological Overview, and Future Prospects

Porcine reproductive and respiratory syndrome (PRRS) remains a formidable challenge for the global pig industry. Caused by PRRS virus (PRRSV), this disease primarily affects porcine reproductive and respiratory systems, undermining effective host interferon and other immune responses, resulting in vaccine ineffectiveness. In the absence of specific antiviral treatments for PRRSV, vaccines play a crucial role in managing the disease. The current market features a range of vaccine technologies, including live, inactivated, subunit, DNA, and vector vaccines, but only modified live virus (MLV) and killed virus (KV) vaccines are commercially available for PRRS control. Live vaccines are promoted for their enhanced protective effectiveness, although their ability to provide cross-protection is modest. On the other hand, inactivated vaccines are emphasized for their safety profile but are limited in their protective efficacy. This review updates the current knowledge on PRRS vaccines' interactions with the host interferon system, and other immunological aspects, to assess their current status and evaluate advents in PRRSV vaccine development. It presents the strengths and weaknesses of both live attenuated and inactivated vaccines in the prevention and management of PRRS, aiming to inspire the development of innovative strategies and technologies for the next generation of PRRS vaccines.

Prevalence, Time of Infection, and Diversity of Porcine Reproductive and Respiratory Syndrome Virus in China

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.

Isolation and pathogenicity comparison of two novel natural recombinant porcine reproductive and respiratory syndrome viruses with different recombination patterns in Southwest China

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses in the swine industry. Frequent mutations and recombinations account for PRRSV immune evasion and the emergence of novel strains. In this study, we isolated and characterized two novel PRRSV-2 strains from Southwest China exhibiting distinct recombination patterns. They were designated SCABTC-202305 and SCABTC-202309. Phylogenetic results indicated that SCABTC-202305 was classified as lineage 8, and SCABTC-202309 was classified as lineage 1.8. Amino acid mutation analysis identified unique amino acid substitutions and deletions in ORF5 and Nsp2 genes. The results of the recombination analysis revealed that SCABTC-202305 is a recombinant with JXA1 as the major parental strain and NADC30 as the minor parental strain. At the same time, SCABTC-202309 is identified as a recombinant with NADC30 as the major parental strain and JXA1 as the minor parental strain. In this study, we infected piglets with SCABTC-202305, SCABTC-202309, or mock inoculum (control) to study the pathogenicity of these isolates. Although both isolated strains were pathogenic, SCABTC-202305-infected piglets exhibited more severe clinical signs and higher mortality, viral load, and antibody response than SCABTC-202309-infected piglets. SCABTC-202305 also caused more extensive lung lesions based on histopathology. Our findings suggest that the divergent pathogenicity observed between the two novel PRRSV isolates may be attributed to variations in the genetic information encoded by specific genomic regions. Elucidating the genetic determinants governing PRRSV virulence and transmissibility will inform efforts to control this devastating swine pathogen.IMPORTANCEPorcine reproductive and respiratory syndrome virus (PRRSV) is one of the most critical pathogens impacting the global swine industry. Frequent mutations and recombinations have made the control of PRRSV increasingly difficult. Following the NADC30-like PRRSV pandemic, recombination events involving PRRSV strains have further increased. We isolated two novel field PRRSV recombinant strains, SCABTC-202305 and SCABTC-202309, exhibiting different recombination patterns and compared their pathogenicity in animal experiments. The isolates caused higher viral loads, persistent fever, marked weight loss, moderate respiratory clinical signs, and severe histopathologic lung lesions in piglets. Elucidating correlations between recombinant regions and pathogenicity in these isolates can inform epidemiologic tracking of emerging strains and investigations into viral adaptive mechanisms underlying PRRSV immunity evasion. Our findings underscore the importance of continued genomic surveillance to curb this economically damaging pathogen.

Diltiazem HCl suppresses porcine reproductive and respiratory syndrome virus infection in susceptible cells and in swine

Porcine reproductive and respiratory syndrome virus (PRRSV) is a pathogen for swine, resulting in substantial economic losses to the swine industry. However, there has been little success in developing effective vaccines or drugs for PRRSV control. In the present study, we discovered that Diltiazem HCl, an inhibitor of L-type Ca2+ channel, effectively suppresses PRRSV replication in MARC-145, PK-15CD163 and PAM cells in dose-dependent manner. Furthermore, it demonstrates a broad-spectrum activity against both PRRSV-1 and PRRSV-2 strains. Additionally, we explored the underlying mechanisms and found that Diltiazem HCl -induced inhibition of PRRSV associated with regulation of calcium ion homeostasis in susceptible cells. Moreover, we evaluated the antiviral effects of Diltiazem HCl in PRRSV-challenged piglets, assessing rectal temperature, viremia, and gross and microscopic lung lesions. Our results indicate that Diltiazem HCl treatment alleviates PRRSV-induced rectal temperature spikes, pulmonary pathological changes, and serum viral load. In conclusion, our data suggest that Diltiazem HCl could serve as a novel therapeutic drug against PRRSV infection.

Simultaneous Detection of Porcine Respiratory Coronavirus, Porcine Reproductive and Respiratory Syndrome Virus, Swine Influenza Virus, and Pseudorabies Virus via Quadruplex One-Step RT-qPCR

Porcine respiratory coronavirus (PRCoV), porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), and pseudorabies virus (PRV) are significant viruses causing respiratory diseases in pigs. Sick pigs exhibit similar clinical symptoms such as fever, cough, runny nose, and dyspnea, making it very difficult to accurately differentially diagnose these diseases on site. In this study, a quadruplex one-step reverse-transcription real-time quantitative PCR (RT-qPCR) for the detection of PRCoV, PRRSV, SIV, and PRV was established. The assay showed strong specificity, high sensitivity, and good repeatability. It could detect only PRCoV, PRRSV, SIV, and PRV, without cross-reactions with TGEV, PEDV, PRoV, ASFV, FMDV, PCV2, PDCoV, and CSFV. The limits of detection (LODs) for PRCoV, PRRSV, SIV, and PRV were 129.594, 133.205, 139.791, and 136.600 copies/reaction, respectively. The intra-assay and inter-assay coefficients of variation (CVs) ranged from 0.29% to 1.89%. The established quadruplex RT-qPCR was used to test 4909 clinical specimens, which were collected in Guangxi Province, China, from July 2022 to September 2023. PRCoV, PRRSV, SIV, and PRV showed positivity rates of 1.36%, 10.17%, 4.87%, and 0.84%, respectively. In addition, the previously reported RT-qPCR was also used to test these specimens, and the agreement between these methods was higher than 99.43%. The established quadruplex RT-qPCR can accurately detect these four porcine respiratory viruses simultaneously, providing an accurate and reliable detection technique for clinical diagnosis.

Tissue expression of porcine transient receptor potential mucolipin protein channels and their differential responses to porcine reproductive and respiratory syndrome virus infection in vitro

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) infection results in a serious disease, posing a huge economic threat to the global swine industry. The transient receptor potential mucolipin proteins (TRPMLs) have been shown to be strongly associated with virus infection and other physiological processes in humans, but their tissue distribution and responses to PRRSV in pigs remain unknown.

Material and Methods

Quantitative reverse-transcription PCR analysis was undertaken to determine the optimal primer for TRPML expression detection and for quantifying that expression individually in different pig tissue samples. Meat Animal Research Center 145 (MARC-145) monkey kidney cells and the TRPML-specific activator mucolipin synthetic agonist 1 (ML-SA1) were used to reveal the relationship between TRPML and PRRSV-2 infection.

Results

The best primers for each TRPML gene used in a fluorescence-based quantitative method were identified and TRPML1 was found to be highly expressed in the kidneys and liver of pigs, while TRPML2 and TRPML3 were observed to be primarily expressed in the kidney and spleen tissues. The expression of TRPML2 was upregulated with the rise in PRRSV-2 infection titre but not the expression of TRPML1 or TRPML3, and ML-SA1 inhibited PRRSV-2 in a dose-dependent manner.

Conclusion

Our research revealed the gene expression of TRPMLs in pigs and identified that TRPML channels may act as key host factors against PRRSV infection, which could lead to new targets for the prevention and treatment of pig infectious diseases.