Genomic characteristics and epidemic trends of NADC30-like PRRSV in China

BACKGROUND

NADC30-like PRRSV was first identified in China in 2012 and had become the predominant circulating strain since 2016. Currently, the recombination patterns of NADC30-like PRRSV in China exhibit a high degree of complexity, characterized by low whole-genome sequence homology. The genomic features and epidemiological trends of these strains remain to be elucidated.

RESULTS

To evaluate the prevalence of NADC30-like PRRSV in China, this study acquired 30 whole-genome sequences of NADC30-like strains via Next-Generation Sequencing (NGS). These sequences were subsequently integrated with 224 whole-genome sequences from China available in the GenBank database. A comprehensive analysis of the genomic characteristics of contemporary NADC30-like PRRSV strains in China was conducted. Recombinant analysis indicated a yearly increase in the number of NADC30-like strains exhibiting recombination signals, whereas nonrecombinant NADC30-like strains have become nearly extinct. Among the recombination events, those involving L1C and L8E as parental strains are most prevalent. Based on the results of recombination and phylogenetic analyses, this study classified 120 Chinese NADC30-like strains with similar recombination characteristics into groups NADC30-R1 to R12. The intra-group genetic distances of the NADC30-R1 to R12 groups approximately 5.73% (SD ± 1.68), while the inter-group genetic distances between different groups are usually stably greater than 10%. The amino acid alignment of Nsp2 demonstrated that all NADC30-R1 to R12 strains exhibit a discontinuous deletion of 131 amino acids. These classifications do not exhibit consistent pathogenic characteristics within groups, with most NADC30-like PRRSVs showing moderate virulence. Geographical distribution analysis indicated that NADC30 whole-genome sequences in China originated from 19 provinces. Notably, the NADC30-R1 and NADC30-R2 strains are the most widely distributed and abundant, suggesting that these variants have established localized epidemics in specific regions.

CONCLUSION

In summary, the vast majority of NADC30-like strains in our country have undergone recombination, L1C + L8E is the most common recombination mode. The NADC30-like strains in China can be classified into 12 different recombination patterns, NADC30-R1 and NADC30-R2 strains are already showing pandemic trends. These findings provide a critical foundation for future NADC30-like PRRSV prevention and control strategies.

Genetic characterization and pathogenicity of two recombinant PRRSV-2 strains from lineages 1, 3, 5, and 8 emerged in China

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major economic threat to the global swine industry. Currently, NADC30-like PRRSV has undergone complex recombination with local Chinese strains, which has exacerbated the evolution of PRRSV. Recently, new recombinant PRRSV-2 strains from four lineages (lineages 1, 3, 5, and 8) have emerged in China. However, information on the pathogenicity of the novel isolate in China remains limited. To further our knowledge about the isolate, FJLIUY2017 and PRRSV2/CN/G8/2018 were selected to analyze their pathogenicity for piglets.

METHODS

The PRRSV FJLIUY2017 and PRRSV2/CN/G8/2018 strains were isolated by porcine alveolar macrophages (PAMs) and MARC-145CD163. Complete genomic sequence analyses were conducted using the DNASTAR 7.0 software and the phylogenetic tree was constructed with MEGA 7.0. Recombination events were detected using RDP V4.10 and SIMPLOT software 3.5.1. Five PRRSV-free per group were inoculated with 2 mL (2 × 105 TCID50) of the FJLIUY-2017 and PRRSV2/CN/G8/2018. Clinical signs of disease were recorded daily after challenge. Blood samples were collected from all piglets on days 0, 4, 7, 11, and 14 dpi for analysis of viral load by IFA and PRRSV-specific antibody levels by ELISA kit. Lung gross and microscopic lesions of the inoculated piglets were examined by scoring system for lung lesion.

RESULTS

Full-length genome analysis revealed that FJLIUY2017 and PRRSV2/CN/G8/2018 share 89.2% identity with each other, and in particular, they had a low degree of homology (< 92%) with PRRSV sequences available in GenBank. Phylogenetic and recombination analyses revealed that the two strains were recombinant viruses from lineages 1, 3, 5.1, and 8.7 strains. Animal studies indicated that FJLIUY-2017 resulted in the typical clinical signs of PRRSV, including persistent fever, higher viremia, severe lung lesions, and 20% mortality, whereas PRRSV2/CN/G8/2018 caused moderate clinical symptoms and no mortality during the challenge period. Hyper-immune sera against the major vaccine strains JXA1-R (lineage 8) and Ingelvac PRRS MLV (Lineage 5) failed to neutralize two strains.

CONCLUSIONS

FJLIUY-2017 caused persistent fever, higher viremia, 20% mortality and exhibited higher pathogenicity in piglets compared to PRRSV2/CN/G8/2018. Our results suggest that recombination between different PRRSV-2 lineages can result in the development of PRRSV variants with increased pathogenicity.

A serologic marker attenuated live vaccine protects piglets against highly pathogenic porcine reproductive and respiratory syndrome virus infection

Currently, there are no commercial serologic marker or differentiation of infected and vaccinated animal (DIVA) vaccines for the eradication of porcine reproductive and respiratory syndrome virus (PRRSV) infection from pig farms. In a previous study, a nanobody-based competitive ELISA (cELISA) was specifically developed to detect anti-genotype 2 PRRSV (PRRSV-2) antibodies. On the basis of the epitope recognized by the nanobody and the prevalence of PRRSV-2 infection in China, a DIVA vaccine candidate strain was designed and evaluated in the present study. First, an infectious cDNA clone based on the genomic sequence of the highly pathogenic PRRSV-2 (HP-PRRSV) isolate SX-HD was constructed and named rSX-HD. Using the infectious clone as the backbone, a chimeric infectious cDNA clone in which the gene encoding the nucleocapsid (N) protein was replaced with the gene encoding the genotype 1 PRRSV N protein was generated and named rSX-HD2M1. The chimeric PRRSV rSX-HD2M1 was subsequently rescued successfully in Marc-145 cells, which were then passaged for 120 generations for attenuation. A safety study indicated that rSX-HD2M1-F120 is not pathogenic to piglets. In vivo inoculation and challenge experiments suggested that rSX-HD2M1-F120 vaccination significantly reduced serum viral loads and lung tissue lesions and that vaccinated piglets did not show any clinical symptoms or histopathological changes. Furthermore, this recombinant marker virus, in conjunction with the previously developed nanobody-based cELISA, enables serological differentiation between marker virus-infected animals and those infected with wild-type PRRSV-2. These results suggest that rSX-HD2M1-F120 is a good candidate for providing a live attenuated DIVA vaccine against PRRSV-2 infection in piglets.

Pathogenicity and antigenic characterization of a novel highly virulent lineage 3 porcine reproductive and respiratory syndrome virus 2

BACKGROUND/PURPOSE

Porcine reproductive and respiratory syndrome virus (PRRSV) is a pathogen with a negative economic impact on the global swine industry. In 2019, a suspected highly pathogenic strain, NPUST-108-929/2019 (108-929), was isolated from a pig farm in Pingtung with an outbreak of high mortality and analyzed. The characteristics of PRRSV 108-929 have barely been studied.

METHODS

This study was to evaluate pathogenicity through animal challenge experiments using PRRSV 108-929 and antigenic characterization of this novel PRRSV.

RESULTS

This PRRSV strain is PRRSV 2, belonging to lineage 3 based on open reading frame 5 sequence analysis. Four putative N-linked glycosylation sites (N32, N35, N44 and N51) are located on glycoprotein 5. Experimental results revealed that high fever occurred at 3 days postinoculation (dpi) in the high-titer inoculation (HIN) group (2 × 104 TCID50/mL), 8 dpi in the high-titer contact (HC) group, 4 dpi in the low-titer inoculation (LIN) group (2 × 103 TCID50/mL) and 9 dpi in the low-titer contact (LC) group. All pigs in each PRRSV 108-929 challenge and contact group showed severe clinical signs, such as high fever (>40.5 °C) and significant weight loss. Deaths occurred only in the HIN group; the survival rate was 60 %. All the piglets except the control group piglets showed high viremia titers (6.04-8.28 log10 copies/μL).

CONCLUSION

The pathogenic characteristics of PRRSV 108-929 suggest that it is a highly virulent PRRSV strain at both the farm and laboratory levels.

Analysis of the genetic evolution and recombination of the PRRSV-2 GP2 protein in China from 1996 to 2023

Porcine reproductive and respiratory syndrome (PRRS) is among the most serious infectious diseases of pigs worldwide. It is caused by PRRSV and frequently mutates and recombines. To date, however, there have been relatively few studies that have analyzed the GP2 membrane protein of this virus. In this study, we compared 570 nucleotide sequences of the PRRSV-2 GP2 protein obtained from the NCBI GenBank database, which were subjected to phylogenetic analysis. We selected 64 representative strains to investigate the genetic evolution and recombination of the GP2 protein in China. Lineages 1 and 8 were the most prevalent, while lineages 5 and 8 showed closer genetic relationships. The nucleotide similarities of the 570 GP2 sequences ranged from 83.0% to 100%, with amino acid similarities from 80.2% to 100%. Recombinant analysis indicated lineage 1 strains had the highest recombination probability. Comparison of amino acid sequences showed substitutions without deletions or insertions, with lineage 1 exhibiting the most substitutions and lineage 8 the fewest. These findings enhance understanding of PRRSV-2 genetic variation and provide a foundation for further studies on GP2 and vaccine development.

IMPORTANCE

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused significant losses and posed threats to the swine breeding industry. To date, there have been comparatively few studies on the GP2 protein of PRRSV-2, and consequently, many unanswered questions remain regarding its pathogenicity-associated mechanisms and effects. We collected 570 nucleotide sequences of the GP2 protein of this virus and used these data to perform multifaceted analytical work in order to facilitate the understanding of the genetic evolution of this virus and recombinant mutations. These provide basic data for the follow-up study of GP2 and lay a foundation for further in-depth studies of this virus and vaccine development.

The role of major and minor structural proteins of porcine reproductive and respiratory syndrome virus in induction of protective immunity

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV), an economically significant threat to the world pork production, is notoriously known for its heterogeneity, and therefore the current vaccines often fail to provide efficient cross-protection against diverse PRRSV strains.

Methods

By making chimeric viruses using HP-PRRSV-2 lineage 8 (JXwn06) and lineage 1 NADC30-like strains (CHsx1401) as model organisms, the recently results have shown that the viral structural protein-coding region is critical for induction of homologous immunity. In this study, the chimeric viruses were further constructed by exchanging the region coding for the minor (GP2/3/4) or major (GP5/M) structural proteins of JXwn06 on the backbone of CHsx1401 to generate two mutants CHsx1401-GP234JX and CHsx1401-GP5MJX.

Results

The subsequent animal experiment showed that all three chimeras could confer good protective immunity against the lethal challenge by HP-PRRSV strain JXwn06, and the survived pigs had much lower lung lesions, faster viremia clearance, and lower viral tissue load. However, the exchange of SP region as a whole performed better than either GP2/3/4 or GP5/M region alone, as the pigs in the latter groups showed transient fever following challenge and higher viral load in certain tissues, highlighting a synergistic role. Interestingly, as compared to the group CHsx1401-GP234JX, the group CHsx1401-GP5MJX showed excellent viremia clearance, comparable to the SP group.

Discussion

Our results in this report revealed the important role of ORFs2-4 and ORFs5-6 regions in induction of protective immunity and have important implications in understanding viral pathogenesis and further vaccine development.

Development of blocking ELISA for detection anti-PRRSV antibodies and serological investigation of PRRSV in China

Porcine reproductive and respiratory syndrome virus (PRRSV) demonstrates a significantly high prevalence among swine populations. Monoclonal antibodies (mAbs) with high affinity for conserved epitopes of PRRSV can facilitate the development of a broad-spectrum detection method for this virus. This study identified two PRRSV-specific mAbs, designated 2B1 and 2C6, which recognized two conformation-dependent epitopes through indirect immunofluorescence assay (IFA) and Western blot analysis. Further investigation via immunoprecipitation and eukaryotic expression studies confirmed that both mAbs specifically target the Nucleocapsid (N) protein of PRRSV. Importantly, these two epitopes exhibit high conservation across PRRSV isolates, including DV, CH-1a, HuN4, NADC30-like strains, NADC34-like strains and VR2332. The mAb 2C6 was effectively blocked by sera from pigs positive for PRRSV-1 and PRRSV-2. Consequently, a blocking enzyme-linked immunosorbent assay (b-ELISA) based on 2C6 was developed to detect anti-PRRSV antibodies, achieving enhanced sensitivity and specificity. The results obtained using this method demonstrated a higher concordance rate compared to those derived from commercial kit. Additionally, a total of 451 animals from various provinces in China were sampled, revealing an overall IgG antibody seropositivity against PRRSV of 77.38 % (349/451), with nursery pigs at 33.48 % (151), growing pigs at 15.96 % (72), fattening pigs at 39.69 % (179) and sows at 10.86 % (49). Collectively, the established b-ELISA represents an optimal method for large-scale serological investigations into PRRSV antibodies within farming operations.

Comparative Genomic and Biological Investigation of NADC30- and NADC34-Like PRRSV Strains Isolated in South Korea

Porcine reproductive and respiratory syndrome virus (PRRSV) is a globally endemic, costly swine arterivirus with wide genetic and antigenic variations, leading to the frequent appearance of novel virulent strains that hampers PRRSV control. Recently, NADC30-like (lineage 1C, L1C) and NADC34-like (lineage 1A, L1A) PRRSV strains were reported to be prevalent in mainland South Korea and became the main epidemic strains persistently attributed to PRRSV outbreaks nationwide, raising great concern in the domestic pork industry. Although the genotypic and pathotypic variability of NADC30- and NADC34-like viruses has been explored in the United States and China, their genomic and biological characteristics have been scarcely studied in South Korea. Here, NADC34-like GNU-2353 and NADC30-like GNU-2377 strains were independently identified from vaccinated swine herds experiencing high piglet mortality. Whole-genome sequencing and phylogenetic analysis revealed that GNU-2353 and GNU-2377 clustered into sublineages L1A (NADC34-like) and L1C (NADC30-like), respectively, sharing high genomic homology with their corresponding lineage-representative strains and harboring the same molecular signatures of continuous 100 and discontinuous 131 amino acid deletions in the nsp2-coding region, respectively. Recombination detection indicated that GNU-2353 and GNU-2377 were recombinants and evolved through natural interlineage recombination between NADC34-like (L1A, major parent) or NADC30-like (L1C, major parent) and RespPRRS modified live virus (MLV)-like (lineage 5, minor parent) strains, respectively. Both viruses displayed homogenous growth kinetics but replicated faster than the prototype VR-2332 in a porcine alveolar macrophage cell line (PAM-KNU). The transcriptional profiles of immune response genes in infected PAM-KNU cells varied between the isolates and VR-2332; particularly, interleukin-10 expression was dramatically upregulated in cells infected with GNU-2353 and GNU-2377. Piglets with GNU-2353 and GNU-2377 infection had high fever; weight loss; increased viremia and nasal shedding; viral distribution in various tissues; thymic atrophy; and apparent macroscopic and microscopic lung lesions, including interstitial pneumonia and viral colonization, compared with control piglets, suggesting that both isolates were virulent to pigs. Remarkably, GNU-2353 caused higher fever, mortality rate (40%) with cyanosis, viremia, and viral shedding within 2 weeks and significantly higher viral loads in several organs than GNU-2377 infection. Thus, NADC34-like GNU-2353 was more pathogenic than NADC30-like GNU-2377. Our findings provide insights into the current epizootic circumstance of NADC30- and NADC34-like PRRSV in South Korea and can aid in tailoring improved control strategies.

Porcine ISG15 fused IFN-λ3 as a novel antiviral agent for treating porcine reproductive and respiratory syndrome virus infection in vivo

IFN-λs hold promise as therapeutic candidates against mutable respiratory viruses, but their efficacy against porcine reproductive and respiratory syndrome virus (PRRSV) remains unclear. In this study, we expressed a recombinant fusion protein consisting of porcine ISG15 linked porcine IFN-λ3 (ISG15-IFN-λ3) via a rigid protein linker in Escherichia coli (E. coli). In vitro experiments demonstrated that treatment of porcine alveolar macrophage (PAM)-derived CRL-2843 cells with ISG15-IFN-λ3 induced upregulation of several Interferon-stimulated Genes (ISGs) proteins, including ISG15, ISG56, and HERC5. CRL-2843 cells pretreated with ISG15-IFN-λ3 exhibited heightened resistance to Newcastle disease virus infection, while PRRSV-permissive cells treated with ISG15-IFN-λ3 before and during PRRSV exposure showed significantly inhibited PRRSV replication as well. In animal experiments, at 21 days post-infection, ISG15-IFN-λ3-treated piglets displayed milder lung tissue pathology and significantly reduced serum PRRSV-RNA, indicating enhanced viral clearance and faster recovery. Additionally, PAMs collected from ISG15-IFN-λ3-treated piglets showed significantly reduced mRNA expression of representative cytokines, chemokines, suggesting that ISG15-IFN-λ3 treatment may mitigate pneumonia severity by reducing the levels of these inflammatory mediators. These findings indicate that recombinant ISG15-IFN-λ3 expressed in E. coli may serve as a novel, effective, and affordable agent for treating severe PRRSV infection in piglets, potentially benefiting the pork industry.

Current Status of Porcine Reproductive and Respiratory Syndrome Vaccines

Porcine reproductive and respiratory syndrome (PRRS), characterized by reproductive failures in breeding pigs and respiratory diseases in growing pigs, is a widespread and challenging disease. The agent, PRRSV, is a single-strand RNA virus that is undergoing continuous mutation and evolution, resulting in the global spread of multiple strains with different genetic characteristics and variable antigens. There are currently no effective measures to eradicate PRRS, and vaccination is crucial for controlling the disease. At present, various types of vaccine are available or being studied, including inactivated vaccines, modified live virus (MLV) vaccines, vector vaccines, subunit vaccines, DNA vaccines, RNA vaccines, etc. MLV vaccines have been widely used to control PRRSV infection for more than 30 years since they were first introduced in North America in 1994, and have shown a certain efficacy. However, there are safety and efficacy issues such as virulence reversion, recombination with field strains, and a lack of protection against heterologous strains, while other types of vaccine have their own advantages and disadvantages, making the eradication of PRRS a challenge. This article reviews the latest progress of these vaccines in the prevention and control of PRRS and provides scientific inspiration for developing new strategies for the next generation of PRRS vaccines.

Comparison of pathogenicity and host responses of emerging porcine reproductive and respiratory syndrome virus variants in piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly variable virus with genetic diversity. This study comparatively examines the pathogenicity and immunological impact of two emergent PRRSV strains, SD53 and HuN4, in piglets. Our results indicate that SD53 strain induces milder clinical syndromes and less severe tissue damage than HuN4, despite similar replication rates. Hematological tests showed less perturbations in peripheral blood cell profiles after SD53 infection, suggesting a less systemic impact. The neutrophil-to-lymphocyte ratio was notably lower in SD53-infected piglets, suggesting a less intense inflammatory reaction. Moreover, SD53 infection led to lower levels of pro-inflammatory cytokines, further supporting a less pronounced inflammatory profile. Both strains induced the production of PRRSV-specific antibodies. However, transcriptomic analysis of lung and lymph node tissues from infected piglets disclosed a more moderate up-regulation of core genes, including ISGs, in the SD53 group. Further analysis indicated that SD53 primarily enhanced immune-related signaling, particularly in T cell response modules, while HuN4 caused a more robust pro-inflammatory reaction and a dampening of T cell functionality. Flow cytometry analyses confirmed these findings, showing higher CD4/CD8 ratios and increased CD4+ T cell percentages in SD53-infected piglets, implying a more robust T cell response. Collectively, these findings broaden our comprehension of PRRSV pathogenesis and may inform the development of future therapeutic or prophylactic strategies for controlling PRRSV infections more effectively.

IMPORTANCE

The high mutation rate of porcine reproductive and respiratory syndrome virus (PRRSV) poses significant challenges to its accurate diagnosis and the implementation of effective control measures. This research explores the pathogenic profiles of two emerging PRRSV stains: the NADC30-like strain SD53 and the highly pathogenic strain HuN4. Our investigation reveals that SD53 initiates distinct immunopathological responses in vivo compared with those provoked by HuN4. By conducting a transcriptome analysis of differential gene expression in the lungs and lymph nodes of infected piglets, we unveil the intricate molecular mechanisms underlying the contrasting pathogenicity of these two strains. The comprehensive insights yielded by this study are instrumental in advancing our understanding of the dominant NADC30-like PRRSV strain, which has become increasingly prevalent in China's swine industry.

Recombinant characterization and pathogenicity of a novel L1C RFLP-1-4-4 variant of porcine reproductive and respiratory syndrome virus in China

Porcine reproductive and respiratory syndrome (PRRS) is one of the most significant diseases affecting the pig industry worldwide and is caused by the PRRS virus (PRRSV), which has complex genetic variation due to frequent mutations, indels, and recombination. The emergence of PRRSV L1C.5 in 2020 in the United States has raised worldwide concerns about PRRSV with the RFLP 1-4-4 pattern and lineage 1C. However, studies on the pathogenic characteristics, epidemiological distribution, and effectiveness of vaccines against PRRSV with L1C and RFLP1-4-4 pattern in China are still insufficient. In this study, a novel recombinant variant of PRRSV with RFLP 1-4-4 and lineage 1C features, different from L1C.5 in the United States, was isolated in China in 2021. In pathogenicity experiments in specific pathogen-free piglets or farm piglets, 60-100% of artificially infected experimental piglets died with high fever and respiratory symptoms. Inflammatory cytokine and chemokine levels were upregulated in infected piglets. A commercially modified live vaccine against highly pathogenic PRRSV did not provide effective protection when the vaccinated piglets were challenged with the novel L1C-1-4-4 variant. Therefore, this strain merits special attention when devising control and vaccine strategies. These findings suggest that extensive joint surveillance is urgently needed and that vaccine strategies should be updated to prevent the disease from spreading further.

Pathogenic Characteristics of Five Different Lineage of Korean PRRSV-2 Isolates (NADC30-Like, VR2332-Like, LKA, LKB, and LKC)

Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant pathogen in the worldwide swine industry. The virus shows high genetic variation coupled with a broad range of virulence in pigs. Although multiple lineages of the virus have been prevalent throughout in Korea, the characteristics of lineage-wise pathogenicity are largely unknown. Therefore, this study was designed to analyze and compare the pathogenicity of 11 representative Korean PRRSV-2 isolates selected from PRRSV-2 lineages circulating in Korea, NADC30-like, VR2332-like, and three nation-specific lineages (lineage KOR A (LKA), lineage KOR B (LKB), and lineage KOR C (LKC)), which have been continuously prevalent in the nation. Eleven groups of pigs were experimentally infected with one Korean PRRSV-2 isolate through four consecutive animal experiments. Body weight and body temperature were recorded during each 4-week challenge experiment period, and virological, serological, and histopathological tests were performed on the collected samples. The data from the animal experiments were integrated into two indicators-excretion and clinical signs-through correlation and principal component analysis (PCA). Meta-analysis was used to compare PRRSV-2 isolates using each indicator. Based on these analyses, while L1C viruses used in this study (JB15-N-P31-GB and JB15-N-PJ73-GN, similar to NADC30-like strains) exhibited low or moderate levels of excretion and clinical signs, lineage 5 (L5) or modified live vaccine (MLV)-variant strains exhibited high levels of excretion compared to other PRRSV-2 isolates. However, the L5 variants all caused mild clinical signs, except for JB15-N-PJ4-GN, which showed the 4th highest clinical sign indicator. Among the Korean lineages (LKA, LKB, and LKC), two LKB strains (GGYC45 and JB15-N-PJ10-GN) were the most virulent as they showed the highest mortality after the challenge. On the other hand, the LKA and LKC viruses displayed lower excretion indicators than L5 strains, but they had higher-ranked clinical sign indicators than low-virulence L5 MLV variants. In conclusion, PRRSV prevalent in Korea has diverse excretion and clinical characteristics, and certain lineage is highly pathogenic. These results will offer useful insights to prevent spread of PRRSV and improve the efficacy of vaccines in the future.

Genomic and pathogenicity analysis of two novel highly pathogenic recombinant NADC30-like PRRSV strains in China, in 2023

Porcine reproductive and respiratory syndrome viruses (PRRSVs) exhibit high mutability and recombination, posing challenges to their immunization and control. This study isolated two new PRRSV strains, GD-7 and GX-3, from samples collected in Guangdong and Guangxi in 2023. Whole-genome sequencing, along with phylogenetic and recombination analyses, confirmed that GD-7 and GX-3 are natural novel recombinant strains of NADC30 PRRSV. Moreover, we established a pathogenicity model for piglets and sows based on the two isolates. The results of piglet pathogenicity revealed that both GD-7 and GX-3 caused clinical symptoms such as fever, loss of appetite, depression, and slow weight gain. Moreover, we observed that the mortality rate of GD-7-inoculated group piglets was 33.3%, which was similar to that of piglets infected with other highly pathogenic PRRSV strains and exceeded the mortality rate of most NADC30-like PRRSV. In pregnant sow models, the survival rate of sows in the GD-7 group was 75%, in contrast to the GX-3 group, where no sow mortality was observed, and both strains resulted in abortion, mummified fetuses, and stillbirths. These results highlight the elevated pathogenicity of these recombinant strains in sows, with GD-7 mainly causing sows to abort, and GX-3 mainly causing sows to give birth to mummified fetuses. This study introduces two distinct clinical recombinant PRRSV strains that differ from the prevalent strains in China. This research furthers our understanding of the epidemiology of PRRSV and underscores the significance of ongoing monitoring and research in the face of evolving virus strains. Moreover, these discoveries act as early warnings, underscoring the necessity for active control and immunization against PRRSV.IMPORTANCESince the discovery of NADC30-like PRRSV in China in 2013, it has gradually become the dominant strain of PRRSV in China. NADC30-like PRRSV exhibits high recombination characteristics, constantly recombining with different strains, leading to the emergence of numerous novel strains. Of particular importance is the observation that NADC30-like PRRSV with different recombination patterns exhibits varying pathogenicity, which has a significant impact on the pig farming industry. This emphasizes the necessity of monitoring and responding to evolving PRRSV strains to develop effective immunization and control strategies. In this paper, we conducted pathogenicity studies on the isolated NADC30-like PRRSV and analyzed the differences in the genomes and pathogenicity of the different strains by recording clinical symptoms, temperature changes, detoxification tests, and changes in viremia and histopathology in infected pigs. This was done to provide a theoretical basis for the epidemiological situation and epidemic prevention and control of PRRSV.

Generation of an infectious cDNA clone for NADC30-like PRRSV

The porcine reproductive and respiratory syndrome virus (PRRSV) is a highly significant infectious disease that poses a substantial threat to the global pig industry. In recent years, the NADC30-like strain has gradually emerged as prevalent in China, causing a profound impact on the country's pig farming industry. Therefore, it is important to conduct an in-depth study on the characteristics and gene functions of the NADC30-like strain. An infectious cDNA clone is an indispensable tool for investigating the functions of viral genes. In this current study, we successfully isolated a NADC30-like strain and constructed its full-length infectious cDNA clone. The utilization of this clone will facilitate our investigation into the viral replication, pathogenesis, and immune response associated with the PRRSV NADC30-like strain.

Molecular epizootiology of porcine reproductive and respiratory syndrome virus in the Xinjiang Uygur Autonomous Region of China

Rapid evolution of porcine reproductive and respiratory syndrome virus (PRRSV) is the bottleneck for effective prevention and control of PRRS. Thus, understanding the prevalence and genetic background of PRRSV strains in swine-producing regions is important for disease prevention and control. However, there is only limited information about the epizootiological situation of PRRS in the Xinjiang Uygur Autonomous Region, China. In this study, blood or lung tissue samples were collected from 1,411 PRRS-suspected weaned pigs from 9 pig farms in Changji, Shihezi, and Wujiaqu cities between 2020 and 2022. The samples were first tested by RT-quantitative PCR, yielding a PRRSV-2 positive rate of 53.6%. Subsequently, 36 PRRSV strains were isolated through initial adaptation in bone marrow-derived macrophages followed by propagation in grivet monkey Marc-145 cells. Furthermore, 28 PRRSV-positive samples and 20 cell-adapted viruses were selected for high-throughput sequencing (HTS) to obtain the entire PRRSV genome sequences. Phylogenetic analysis based on the nucleotide sequences of the ORF5 gene of the PRRSV strains identified in this study grouped into sub-lineages 1.8 and 8.7 the former being the dominant strain currently circulating in Xinjiang. However, the NSP2 proteins of the Xinjiang PRRSV strains shared the same deletion patterns as sub-lineage 1.8 prototype strain NADC30 with the exception of 4 strains carrying 2-3 additional amino acid deletions. Further analysis confirmed that recombination events had occurred in 27 of 37 PRRSVs obtained here with the parental strains belonging to sub-lineages 1.8 and 8.7, lineages 3 and 5, with the recombination events having occurred most frequently in the 5' and 3' termini of ORF1a and 5' terminus of ORF1b.

Development of a Ferritin Protein Nanoparticle Vaccine with PRRSV GP5 Protein

Porcine reproductive and respiratory syndrome virus (PRRSV) presents a significant threat to the global swine industry. The development of highly effective subunit nanovaccines is a promising strategy for preventing PRRSV variant infections. In this study, two different types of ferritin (Ft) nanovaccines targeting the major glycoprotein GP5, named GP5m-Ft and (Bp-IVp)3-Ft, were constructed and evaluated as vaccine candidates for PRRSV. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) demonstrated that both purified GP5m-Ft and (Bp-IVp)3-Ft proteins could self-assemble into nanospheres. A comparison of the immunogenicity of GP5m-Ft and (Bp-IVp)3-Ft with an inactivated PRRSV vaccine in BALB/c mice revealed that mice immunized with GP5m-Ft exhibited the highest ELISA antibody levels, neutralizing antibody titers, the lymphocyte proliferation index, and IFN-γ levels. Furthermore, vaccination with the GP5m-Ft nanoparticle effectively protected piglets against a highly pathogenic PRRSV challenge. These findings suggest that GP5m-Ft is a promising vaccine candidate for controlling PRRS.

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.

Recombination of Porcine Reproductive and Respiratory Syndrome Virus: Features, Possible Mechanisms, and Future Directions

Recombination is a pervasive phenomenon in RNA viruses and an important strategy for accelerating the evolution of RNA virus populations. Recombination in the porcine reproductive and respiratory syndrome virus (PRRSV) was first reported in 1999, and many case reports have been published in recent years. In this review, all the existing reports on PRRSV recombination events were collected, and the genotypes, parental strains, and locations of the recombination breakpoints have been summarized and analyzed. The results showed that the recombination pattern constantly changes; whether inter- or intra-lineage recombination, the recombination hotspots vary in different recombination patterns. The virulence of recombinant PRRSVs was higher than that of the parental strains, and the emergence of virulence reversion was caused by recombination after using MLV vaccines. This could be attributed to the enhanced adaptability of recombinant PRRSV for entry and replication, facilitating their rapid propagation. The aim of this paper was to identify common features of recombinant PRRSV strains, reduce the recombination risk, and provide a foundation for future research into the mechanism of PRRSV recombination.

Characterization of a novel recombinant NADC30‑like porcine reproductive and respiratory syndrome virus in Shanxi Province, China

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens affecting the swine industry. In this report, a novel PRRSV strain SXht2012 was isolated from Shanxi province in China. To identify genetic characteristics of SXht2012, we conducted phylogenetic and homology analyses after sequencing its complete genome. The results revealed that SXht2012 belonged to NADC30-like strain and shared 91.3% nucleotide (nt) identity with strain NADC30. Notably, sequence alignment showed that a distinctive feature in the NSP2 region, where a 131-amino acid (aa) deletion was found in the hypervariable region (HVR). Additionally, variations were also detected in the GP5 protein, specifically in the decoy peptide, T cell peptide, and a potential glycosylation site (aa 32). Furthermore, we also found that SXht2012 was likely a recombination virus originating from NADC30-like and JXA1-like strains, and three recombination breakpoints were identified in the genome at nt positions 1516, 5280 and 6851, which correspond to the NSP2, NSP3, and NSP7 regions. Overall, these findings have significant implications for understanding the genetic variation and evolutionary dynamics of PRRSV strains.

Genomic Characterization of HLJDZD55: The First L1B PRRSV in China

Porcine reproductive and respiratory syndrome virus (PRRSV) critically threatens the pig industry in China. Lineage 1 PRRSV, which is divided into L1A-L1F and L1H-L1J, is widely recognized as the most extensively genetically diverse lineage globally. L1A (NADC34-like) and L1C (NADC30-like) PRRSVs have become the current major circulating strains in China. Notably, strains from other branches of L1 have not been reported in China. During our epidemiological investigation of PRRSV, we identified a new strain named HLJDZD55. Phylogenetic analysis of the ORF5 gene revealed that HLJDZD55 belongs to the L1B branch. Alignment of deduced amino acid sequences based on the Nsp2 gene indicated that HLJDZD55 has a discontinuous deletion of 131 amino acids (111 + 1 + 19). We further sequenced the whole genome of HLJDZD55, and phylogenetic analysis based on the whole-genome sequence revealed that HLJDZD55 belongs to the L1C branch. Recombination analysis of the whole genome demonstrated that HLJDZD55 is a recombinant strain of TJZH-1607 (L1C, identified in China) and Minnesota 14 (L1B, identified in the USA). These findings suggested that HLJDZD55 is a newly emerged lineage 1 PRRSV in China and is closely related to L1B PRRSV in the US, which may have been introduced from the U.S. strain and subsequently recombined with the local Chinese strain and underwent evolution. Taken together, these results demonstrated the emergence of L1B PRRSV in China for the first time.

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.

Mass Spectrometry-Based Proteomic Analysis of Potential Host Proteins Interacting with GP5 in PRRSV-Infected PAMs

Porcine reproductive and respiratory syndrome virus (PRRSV) is a typical immunosuppressive virus causing a large economic impact on the swine industry. The structural protein GP5 of PRRSV plays a pivotal role in its pathogenicity and immune evasion. Virus-host interactions play a crucial part in viral replication and immune escape. Therefore, understanding the interactions between GP5 and host proteins are significant for porcine reproductive and respiratory syndrome (PRRS) control. However, the interaction network between GP5 and host proteins in primary porcine alveolar macrophages (PAMs) has not been reported. In this study, 709 GP5-interacting host proteins were identified in primary PAMs by immunoprecipitation coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Bioinformatics analysis revealed that these proteins were involved in multiple cellular processes, such as translation, protein transport, and protein stabilization. Subsequently, immunoprecipitation and immunofluorescence assay confirmed that GP5 could interact with antigen processing and presentation pathways related proteins. Finally, we found that GP5 may be a key protein that inhibits the antigen processing and presentation pathway during PRRSV infection. The novel host proteins identified in this study will be the candidates for studying the biological functions of GP5, which will provide new insights into PRRS prevention and vaccine development.

Protective efficacy of a candidate live attenuated vaccine derived from the SD-R strain of lineage 1 porcine reproductive and respiratory syndrome virus against a lethal challenge with HP-PRRSV HuN4 in piglets

IMPORTANCE

Both highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) and NADC30-like PRRSV have caused tremendous economic losses to the Chinese pig industry. In this study, a good challenge model was established to evaluate the protection afforded by the candidate SD-R vaccine against infection with a representative HP-PRRSV strain (HuN4). The control piglets in the challenge experiment displayed obvious clinical symptoms of PRRSV infection, with a mortality rate up to 40%. In contrast, all the piglets in the vaccinated challenged group survived, and only some pigs had transient fever. The daily gain of SD-R immunized group piglets was significantly increased, and the pathological changes were significantly reduced. In addition, the viral replication levels in the serum of the immunized group were significantly lower than those of the challenged control group. The live attenuated vaccine SD-R strain can provide protection against HP-PRRSV challenge, indicating that the SD-R strain is a promising vaccine candidate for use in the swine industry.

Research Progress of Porcine Reproductive and Respiratory Syndrome Virus NSP2 Protein

Porcine reproductive and respiratory syndrome virus (PRRSV) is globally prevalent and seriously harms the economic efficiency of pig farming. Because of its immunosuppression and high incidence of mutant recombination, PRRSV poses a great challenge for disease prevention and control. Nonstructural protein 2 (NSP2) is the most variable functional protein in the PRRSV genome and can generate NSP2N and NSP2TF variants due to programmed ribosomal frameshifts. These variants are broad and complex in function and play key roles in numerous aspects of viral protein maturation, viral particle assembly, regulation of immunity, autophagy, apoptosis, cell cycle and cell morphology. In this paper, we review the structural composition, programmed ribosomal frameshift and biological properties of NSP2 to facilitate basic research on PRRSV and to provide theoretical support for disease prevention and control and therapeutic drug development.

A Longitudinal Study of NADC34-Like Strains in an Intensive Farm Unravels Divergent Evolution

NADC34-like porcine reproductive and respiratory virus (PRRSV) has had a significant impact on the pig industry, particularly in China. However, the evolutionary characteristics and pathogenicity of NADC34-like PRRSV strains within intensive farming systems are not well understood, particularly regarding the biological characteristic variation of successive outbreaks on a farm. In this study, we conducted continuous surveillance in an intensive farm that experienced a PRRSV outbreak. Two PRRSV strains, GDHZ109/2020 and GDYS162/2022, were isolated and fully sequenced from the same swine farm in Guangdong Province in 2020 and 2022, respectively. Evolutionary analysis based on the ORF5 gene revealed that both strains clustered with NADC34-like strains and shared 96.5% homology. Analysis of the full-length genome and NSP2 gene classified the strains into lineage 1.8, represented by the NADC30 strain. Recombination analysis suggested complex recombination patterns for both strains, involving NADC30-like, NADC34-like, and JXA1-like strains. Although many recombinant regions were nearly identical, there were differences observed in the NSP5-NSP7 region. Pathogenicity experiments conducted on piglets demonstrated that GDHZ109/2020 exhibited higher pathogenicity compared to GDYS162/2022. Piglets in the GDHZ109/2020 infected group had more severe clinical signs and higher mortality. Moreover, analysis of respiratory microbial diversity indicated a significant increase in the abundance of potentially pathogenic microbiota, such as Klebsiella and Erysipelothrix contributing to the respiratory tract of PRRSV-infected piglets, suggesting secondary infections due to differences in immune defense. These findings highlight the importance of NADC34-like recombinant strains' evolution during the farm's epidemic period, which may have contributed to changes in pathogenicity. This study improves our understanding of the current prevalence of PRRSV and provides novel insights into the prevention and control of PRRSV.

Characterization of Rongchang piglets after infection with type 2 porcine reproductive and respiratory syndrome virus strains differing in pathogenicity

Porcine reproductive and respiratory syndrome virus (PRRSV) affects the production and health of pigs and causes severe economic losses to the swine industry worldwide. Different pig breeds have been reported to have different levels of susceptibility to PRRSV, and different PRRSV strains may also influence the infectivity and pathogenicity of the virus. In this study, the susceptibility of Rongchang pigs (a prominent local pig breed in China) to PRRSV infection was thoroughly investigated. Rongchang piglets were exposed to two PRRSV strains: HuN4 (highly pathogenic PRRSV) and SD53-1603 (moderately virulent NADC30-like PRRSV). We observed that Rongchang pigs infected with HuN4 displayed significant clinical manifestations, including fever, reduced body weight, and interstitial pneumonia lesions. Routine blood tests revealed that HuN4-infected pigs exhibited slightly decreased levels of red blood cells, hemoglobin, reticulocytes, and a notable increase in monocytes than control pigs. Additionally, the Rongchang pigs exhibiting severe clinical signs presented a higher neutrophil-to-lymphocyte ratio and a lower lymphocyte-to-monocyte ratio. In contrast, SD53-1603 infection did not cause considerable harm to Rongchang pigs, only resulting in slightly elevated leukocytes and lymphocytes. Furthermore, these two PRRSV strains elicited divergent cytokine responses, such that SD53-1603 infection induced higher levels of TNF-α and IFN-γ, whereas HuN4 infection upregulated IL-1β. These dissimilarities in clinical symptoms, pathological changes, viremia, cytokine expression, and routine blood indices between HuN4 and SD53-1603 infections are critical in understanding the mechanisms of PRRSV infection and developing rational prevention and control strategies against PRRSV.

Epidemiological investigation and pathogenicity of porcine reproductive and respiratory syndrome virus in Sichuan, China

Porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2) lineage 8 was first detected in mainland China in 2006 and has since rapidly spread to become the primary epidemic strain in the country. In this study, samples such as lung tissue, hilar lymph nodes, abortion fetuses, and blood were collected from large-scale pig farms across 11 prefecture-level cities in Sichuan province between 2019 and 2020 for antigen detection and PRRS virus isolation. The antigen detection results indicated that the positive rate of HP-PRRSV (JXA1-Like strain) was 44.74% (51/114), NADC30-Like PRRSV was 17.54% (20/114), and classical PRRSV (VR2332-Like strain) was 37.72% (43/114). The predominant strain was HP-PRRSV. Positive samples were further inoculated into Marc-145 cells for virus isolation and identification, leading to the isolation of a new JXA1-Like PRRSV strain named SCSN2020. The strain was characterized by RT-qPCR, indirect immunofluorescence assay (IFA), plaque purification, electron microscopy, and whole genome sequencing. The total length of the viral genome was determined to be approximately 15,374 bp. A comparison of the SCSN2020 genome with VR2332 revealed that both strains had the same discontinuous 30-amino acid deletion on the Nsp2 gene. ORF5 genotyping classified the SCSN2020 strain as sublineage 8.7, with a whole genome sequence identity of 99.34% with JXA1. Furthermore, we evaluated the pathogenicity of the SCSN2020 strain in 28-day-old piglets and observed persistent fever from day 4 to day 10, weight loss started on day 7, dyspnea and severe lung lesions began started on day 14. The results of this study highlight the current PRRSV epidemic situation in Sichuan province and provide a scientific reference for subsequent prevention and control measures.

Genetic variation and recombination analysis of the GP5 (GP5a) gene of PRRSV-2 strains in China from 1996 to 2022

Porcine reproductive and respiratory syndrome virus (PRRSV) has been prevalent in China for more than 25 years and remains one of the most significant pathogens threatening the pig industry. The high rate of mutation and frequent recombination of PRRSV have exacerbated its prevalence, particularly with the emergence of highly pathogenic PRRSV (HP-PRRSV) has significantly increased the pathogenicity of PRRSV, posing a serious threat to the development of Chinese pig farming. To monitor the genetic variation of PRRSV-2 in China, the GP5 sequences of 517 PRRSV-2 strains from 1996 to 2022 were analyzed and phylogenetic trees were constructed. Furthermore, a total of 60 PRRSV strains, originating from various lineages, were carefully chosen for nucleotide and amino acid homologies analysis. The results showed that the nucleotide homologies of the PRRSV GP5 gene ranged from 81.4 to 100.0%, and the amino acid homologies ranged from 78.1 to 100.0%. Similarly, the PRRSV GP5a gene showed 78.0 ~ 100.0% nucleotide homologies and 70.2 ~ 100.0% amino acid homologies. Amino acid sequence comparisons of GP5 and GP5a showed that some mutations, such as substitutions, deletions, and insertions, were found in several amino acid sites in GP5, these mutations were primarily found in the signal peptide region, two highly variable regions (HVRs), and near two T-cell antigenic sites, while the mutation sites of GP5a were mainly concentrated in the transmembrane and intramembrane regions. Phylogenetic analysis showed that the prevalent PRRSV-2 strains in China were divided into lineages 1, 3, 5, and 8. Among these, strains from lineage 8 and lineage 1 are currently the main prevalent strains, lineage 5 and lineage 8 have a closer genetic distance. Recombination analysis revealed that one recombination event occurred in 517 PRRSV-2 strains, this event involved recombination between lineage 8 and lineage 1. In conclusion, this analysis enhances our understanding of the prevalence and genetic variation of PRRSV-2 in China. These findings provide significant insights for the development of effective prevention and control strategies for PRRS and serve as a foundation for future research in this field.

Genetic and In Vitro Characteristics of a Porcine Circovirus Type 3 Isolate from Northeast China

Porcine circovirus 3 (PCV3) is an emerging virus first discovered in the United States in 2015, and since then, PCV3 has been found in many regions of the world, including America, Asia, and Europe. Although several PCV3 investigations have been carried out, there is a lack of knowledge regarding the pathogenicity of PCV3, mostly due to the limited number of PCV3 isolates that are readily available. In this study, PCV3-DB-1 was isolated in PK-15 cells and characterized in vitro. Electron microscopy revealed the presence of PCV-like particles, and in situ hybridization RNA analysis demonstrated the replication of PCV3 in PK-15 cell culture. Based on phylogenetic analysis of PCV3 isolates from the Heilongjiang province of China, PCV3-DB-1 with 24 alanine and 27 lysine in the Cap protein was originally isolated and determined to belong to the clade PCV3a.

Therapeutic efficacy of tylvalosin combined with Poria cocos polysaccharides against porcine reproductive and respiratory syndrome

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important infectious diseases of pigs worldwide. Vaccination and various management measures have been implemented to control PRRS. However, due to high genetic diversity and insufficient understanding of the pathogenesis and immunological mechanisms, PRRS is still a challenge to the pig industry. Therefore, it is important to develop novel strategies to combat PRRS virus (PRRSV) infection. In this study, our data show that tylvalosin, a third-generation animal-specific macrolide, could inhibit PRRSV replication in MARC-145 cells, and suppress the PRRSV-induced NF-κB activation and cytokines expression. The pig infection experiment further demonstrated that tylvalosin could significantly reduce the virus loads in serum and tissues, and alleviate lung lesions of pigs infected with highly pathogenic PRRSV strains. The fever and loss of daily gain (LoDG) of the pigs were decreased as well. Considering the feature of immune suppression of PRRSV, a combination of tylvalosin with the immunopotentiator Poria cocos polysaccharides (PCP) was developed. Pig experiment showed this combination had a better therapeutic efficacy against PRRSV infection than tylvalosin and PCP alone in attenuating lung lesions, alleviating fever, and suppressing cytokines production. This study suggests that tylvalosin has significant antiviral and anti-inflammatory effects against PRRSV infection, and the combination of tylvalosin and PCP provides a promising strategy for PRRS treatment.

Research Progress on the Development of Porcine Reproductive and Respiratory Syndrome Vaccines

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease in the pig industry, but its pathogenesis is not yet fully understood. The disease is caused by the PRRS virus (PRRSV), which primarily infects porcine alveolar macrophages and disrupts the immune system. Unfortunately, there is no specific drug to cure PRRS, so vaccination is crucial for controlling the disease. There are various types of single and combined vaccines available, including live, inactivated, subunit, DNA, and vector vaccines. Among them, live vaccines provide better protection, but cross-protection is weak. Inactivated vaccines are safe but have poor immune efficacy. Subunit vaccines can be used in the third trimester of pregnancy, and DNA vaccines can enhance the protective effect of live vaccines. However, vector vaccines only confer partial protection and have not been widely used in practice. A PRRS vaccine that meets new-generation international standards is still needed. This manuscript provides a comprehensive review of the advantages, disadvantages, and applicability of live-attenuated, inactivated, subunit, live vector, DNA, gene-deletion, synthetic peptide, virus-like particle, and other types of vaccines for the prevention and control of PRRS. The aim is to provide a theoretical basis for vaccine research and development.

Isolation, identification, and pathogenicity of a NADC30-like porcine reproductive and respiratory disorder syndrome virus strain affecting sow production

Since it was first reported in 1987, porcine reproductive and respiratory syndrome virus (PRRSV) has caused several economic crises worldwide. The current prevalence of PRRSV NADC30-like stains causing clinical disease outbreaks in Chain is highly concerning. Immunization against and the prevention of this infection are burdensome for farming organizations as the pathogen frequently mutates and undergoes recombination. Herein, the genetic characterization of a NADC30-like strain (termed BL2019) isolated from a farm in Guangdong Province, China, was analyzed and its pathogenicity for piglets and sows was assessed. Results revealed that BL2019 exhibits a nucleotide homology of 93.7% with NADC30 PRRSV and its NSP2 coding region demonstrates the same 131aa deletion pattern as that of NADC30 and NADC30-like. Furthermore, we identified two recombination breakpoints located nt5804 of the NSP5-coding region and nt6478 of NSP2-coding region, the gene fragment between the two breakpoints showed higher homology to the TJ strain(a representative strain of highly pathogenic PRRSV) compared to the NADC30 strain. In addition, BL2019 infection in piglets caused fever lasting for 1 week, moderate respiratory clinical signs and obvious visual and microscopic lung lesions; infection in gestating sows affected their feed intake and increased body temperature, abortion rates, number of weak fetuses, and other undesirable phenomena. Therefore, we report a NADC30-like PRRSV strain with partial recombination and a representative strain of HP-PRRSV, strain TJ, that can provide early warning and support for PRRS immune prevention and control.

A New Porcine Reproductive and Respiratory Syndrome Virus with N-Linked Glycosylation Site Deletion in GP5 44th Amino Acid from JXA1, NADC30-Like, and JM Triparental Recombination

Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant pathogen causing substantial financial losses in the global swine industry. The prevention of PRRSV is hampered due to frequent gene recombination among different strains of PRRSV. In this study, a new PRRSV strain, PRRSV-HQ-2020, was identified from nursery piglets in Yunnan Province, China, in 2020. The complete genome analysis revealed that PRRSV-HQ-2020 is highly similar to JXA1-like (lineage 8.7 PRRSV, isolated from China in 2008) in the 5'UTR, nsp1-9, and nsp11 coding regions. Additionally, it has a resemblance to JM (lineage 3 PRRSV, isolated from Taiwan, China, in 2010) in the nsp12-M coding region and NADC30 (lineage 1.8 PRRSV, isolated from North American in 2008) in the nsp10, N, and 3'UTR, suggesting a natural recombination event. Furthermore, recombination analyses showed three interlineage recombination events among lineages 8.7, 1.8, and 3. Notably, the GP5 protein of PRRSV-HQ-2020 exhibited a crucial mutation at position 44, leading to the deletion of a key glycosylation site. These findings provide direct evidence for the natural occurrence of recombination events among three lineages of PRRSV-2 in Chinese swine herds, leading to the emergence of unique genetic properties of PRRSV variants, and providing a theoretical basis for developing better PRRSV prevention strategies.

Comparison of the cross-protection of PPRSV sublineage 8.7 MLV vaccines against the recombinant NADC30-like strain

The emergence of recombinant porcine reproductive and respiratory syndrome virus (PRRSV) has caused a substantial threat to the swine industry in recent years. However, the protective efficacy of different sublineage 8.7 PRRSV modified-live virus (MLV) vaccines against emerging strains were still obscure. In this study, a broad epidemiological investigation of PRRSV showed the prevalence of NADC30-like strain increased in Shandong Province, China from 2018 to 2020. Through piglet trial for vaccination and challenge with recombinant NADC30-like SDlz1601 strain, CH-1R MLV vaccine showed better protective effect than JXA1-R and TJM-F92 MLV vaccines in terms of clinical score and pathological observation. Moreover, all three MLV vaccines could reduce virus loads in the serum of piglets. This study provides valuable insights into the prevalence of the NADC30-like strain and the protective effect of PRRS MLV vaccines against recombinant NADC30-like strains, which could help to improve the prevention and control of PRRSV infections.

Recombination and Mutation in a New HP-PRRSV Strain (SD2020) from China

A new HP-PRRSV strain (SD2020) was isolated from pigs with suspected highly pathogenic porcine reproductive and respiratory syndrome disease in a pig farm in Shandong Province, China, and its genome was sequenced. This pig farm has been using the VR-2332 vaccine strain to immunize pigs for a long time. The phylogenic and single nucleotide polymorphisms (SNPs) analysis of the viruses isolated from dead pigs showed that SD2020 was a natural recombinant virus of the VR-2332 vaccine strain and the JXA1 similar strain, and that two splicing fragments highly homologous to JXA1 in the virus genome were probably derived from the JXA1 wild strain and JXA1-R vaccine strain, respectively. Therefore, the possible recombination events of SD2020 and its mutation site might be related to high pathogenicity.

Variations in the NSP4 gene of the type 2 porcine reproductive and respiratory syndrome virus isolated in China from 1996 to 2021

Porcine reproductive and respiratory syndrome virus (PRRSV) has continuously mutated since its first isolation in China in 1996, leading to difficulties in infection prevention and control. Infections caused by PRRSV-2 strains are the main epidemic strains in China, as determined by phylogenetic analysis. In this study, we focused on the prevalence and genetic variations of the non-structural protein 4 (NSP4) from PRRSV-2 over the past 20 years in China. The fundamental biological properties of the NSP4 were predicted, and an analysis and comparison of NSP4 homology at the nucleotide and amino acid levels was conducted using 123 PRRSV-2 strains. The predicted molecular weight of the NSP4 protein was determined to be 21.1 kDa, and it was predicted to be a stable hydrophobic protein that lacks a signal peptide. NSP4 from different strains exhibited a high degree of amino acid (85.8-100%) and nucleotide sequence homology (81.0-100%). Multiple amino acid substitutions were identified in NSP4 among 15 representative PRRSV-2 strains. Phylogenetic analysis showed that the lineage 8 and 1 strains, the most prevalent strains in China, were indifferent clades with a long genetic distance. This analysis will help fully elucidate the parameters of the PRRSV NSP4 epidemic in China to lay a foundation for adequate understanding of the function of NSP4. Genetic information results from the accumulation of conserved and non-conserved sequences. The high conservation of the NSP4 gene determines the most basic life traits and functions of PRRSV. Analyzing the spatial structure of NSP4 protein and studying the genetic evolution of NSP4 not only provide the theoretical basis for how NSP4 participates in the regulation of the innate response of the host but also provide a target for genetic manipulation and a reasonable target molecule and structure for new drug molecules.

Molecular Characteristics and Pathogenicity of a Novel Recombinant Porcine Reproductive and Respiratory Syndrome Virus Strain from NADC30-, NADC34-, and JXA1-Like Strains That Emerged in China

Recently, the emergence of a NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV), which causes a large number of abortions in swine herds, has raised great concern in China. In this study, a PRRSV variant strain, PRRSV/CN/FJGD01/2021, evolved from recombination between NADC30-like, NADC34-like, and JXA1-like viruses was isolated in Fujian province in 2021, and its pathogenicity in piglets was examined. Animal experiments demonstrated that PRRSV/CN/FJGD01/2021 infection could induce 100% morbidity and cause higher viremia, a persistently higher fever (>40°C for 14 consecutive days), significant weight loss, and severe histopathological lung lesions compared to the NADC30-like FJZ03 strain and NADC34-like FJ0908 strain in piglets. The PRRSV/CN/FJGD01/2021 strain displayed higher pathogenicity than the FJZ03 and FJ0908 strains, but lower pathogenicity than the Chinese highly pathogenic (HP)-PRRSVs in piglets. Moreover, the Ingelvac PRRS modified live vaccine (MLV) provides incomplete cross-protection against heterologous PRRSV/CN/FJGD01/2021 in piglets. Our findings contribute to the understanding of the current epidemic situation of NADC34-like PRRSV in China. IMPORTANCE The pathogenicity of NADC34-like PRRSV has broad variations in virulence. Importantly, NADC34-like PRRSV has undergone complex recombination with local strains since it first emerged in 2017 in China. However, the pathogenicity of the recombinant NADC34-like virus was rarely experimentally evaluated in pigs. In this study, a novel PRRSV strain, PRRSV/CN/FJGD01/2021, was isolated from sows enduring a high-abortion-rate (20%) period in China in 2021. Notably, phylogenetic and recombination analyses revealed that PRRSV/CN/FJGD01/2021 is a recombinant virus from NADC30-, NADC34-, and JXA1-like isolates. PRRSV/CN/FJGD01/2021 was shown to cause higher virus load, persistent fever, significant weight loss, moderate respiratory clinical signs, and severe histopathological lung lesions in piglets. PRRSV/CN/FJGD01/2021 exhibited higher pathogenicity than NADC30-like FJZ03 and NADC34-like FJ0908, but lower than Chinese HP-PRRSVs for piglets. These data indicated that PRRSV/CN/FJGD01/2021 has intermediate virulence for piglets. Furthermore, the Ingelvac PRRS MLV could partly provide protective efficacy against PRRSV/CN/FJGD01/2021 challenge in piglets.

Characterization and Pathogenicity of Two Novel PRRSVs Recombined by NADC30-like and NADC34-like Strains in China

Porcine reproductive and respiratory syndrome viruses (PRRSVs) pose a serious threat to the swine industry in China, which has caused great difficulties for porcine reproductive and respiratory syndrome (PRRS) immune prevention and control, due to its easily mutable and recombinant nature. In this study, two novel PRRSV strains, which were named GD-H1 and GD-F1, were isolated and fully sequenced from pig farms in Guangdong province, China. The phylogenetic analysis and recombination analysis revealed that the GD-H1 and GD-F1 were generated by the recombination of NADC30-like and NADC34-like strains which were different from the previously prevalent strain. Further pathogenic studies on piglets and sows found that the recombinant strains could cause piglets high fever, loss of appetite and lung lesions, but no piglets died. However, the recombinant strains could cause acute death and abortion in pregnant sow infection models together with average survival rates of 62.5% and 37.5% abortion rates, respectively. These findings indicated that the recombinant strains were extremely pathogenic to sows. Therefore, we report two clinical novel recombinant strains of PRRSV that are different from the traditional epidemic strains in China, which may provide early warning and support for PRRS immune prevention and control.

Porcine Reproductive and Respiratory Syndrome Virus (PRRSv): A Cross-Sectional Study on ELISA Seronegative, Multivaccinated Sows

Vaccination against Porcine Reproductive and Respiratory Syndrome virus (PRRSv) is widely used to control clinical disease, but the effectiveness appears in some cases to be suboptimal. Field reports have stated the presence of routinely PRRSv-vaccinated but ELISA seronegative sows: the ELISA non-responders. The real extent of this phenomenon (prevalence–origin–consequences) was not yet investigated. In this study, the prevalence of ELISA non-responders was assessed by measuring PRRSv-specific antibodies in 1400 sows, originating from 70 PRRSv-vaccinating sow herds, using IDEXX ELISA (ELISA 1) and CIVTEST E/S ELISA (ELISA 2). Neutralizing antibodies (NAbs) were quantified in a virus neutralization assay. Univariable logistic regression was used to identify herd risk factors for the presence of ELISA non-responders. The global prevalence of non-responders varied from 3.5% (ELISA 1) to 4.1% (ELISA 2), the herd-level prevalence was 40% and the within-herd prevalence ranged from 5% to 20% (ELISA 1) and from 5% to 30% (ELISA 2). The ELISA non-responders had significantly lower NAbs than the ELISA responders. Herds using the combination of one modified live vaccine and one killed vaccine had a significantly reduced risk of having ELISA non-responders. A first assessment of the prevalence and possible consequences of ELISA non-responders has been provided by this study. The clinical importance, origin and underlying immunological mechanisms warrant further research.

Evolutionary Analysis of Four Recombinant Viruses of the Porcine Reproductive and Respiratory Syndrome Virus From a Pig Farm in China

The porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens causing substantial economic losses to the Chinese swine industry. In this study, we analyzed the complete genome sequences of four PRRSV isolates (PRRSV2/CN/SS0/2020, PRRSV2/CN/SS1/2021, PRRSV2/CN/L3/2021, and PRRSV2/CN/L4/2020) isolated from a single pig farm from 2020 to 2021. The genomes of the four isolates were 14,962–15,023 nt long, excluding the poly (A) tails. Comparative analysis of the genome sequences showed that the four isolates shared 93.2–98.1% homology and they had no close PRRSV relatives registered in the GenBank (&lt;92%). Furthermore, PRRSV2/CN/SS0/2020 and PRRSV2/CN/SS1/2021 had characteristic 150-aa deletions (aa481+aa537-566 +aa628–747) that were identical to the live attenuated virus vaccine strain TJM-F92 (derived from the HP-PRRSV TJ). Further analysis of the full-length sequences suggests that the four isolates were natural recombinant strains between lineages 1 (NADC30-like), 3 (QYYZ-like), and 8.7 (JXA1-like). Animal experiments revealed discrepancies in virulence between PRRSV2/CN/SS0/2020 and PRRSV2/CN/L3/2021. The strain with high homology to HP-PRRSV demonstrates higher pathogenicity for pigs than the other isolate with low homology to HP-PRRSV. Taken together, our findings suggest that PRRSVs have undergone genome evolution by recombination among field strains/MLV-like strains of different lineages.

Paraoxonase-1 Facilitates PRRSV Replication by Interacting with Viral Nonstructural Protein-9 and Inhibiting Type I Interferon Pathway

Paraoxonase-1 (PON1), an esterase with specifically paraoxonase activity, has been proven to be involved in inflammation and infection. Porcine reproductive and respiratory syndrome virus (PRRSV) is still a major concern in pigs and causes severe economic losses to the swine industry worldwide. In this study, the role of PON1 was investigated in porcine alveolar macrophages (PAMs) during PRRSV infection. The results showed that PRRSV replication downregulated PON1, and the knockdown of PON1 significantly decreased PRRSV replication. Similarly, PON1 overexpression could enhance PRRSV replication. Interestingly, we observed that PON1 interacted with PRRSV nonstructural protein 9 (Nsp9), the RNA-dependent RNA polymerase, and the knockdown of PON1 lowered the RNA binding ability of Nsp9, suggesting that PON1 can facilitate Nsp9 function in viral replication. In addition, the knockdown of PON1 expression led to the amplification of type I interferon (IFN) genes and vice versa. In summary, our data demonstrate that PON1 facilitates PRRSV replication by interacting with Nsp9 and inhibiting the type I IFN signaling pathway. Hence, PON1 may be an additional component of the anti-PRRSV defenses.

Evolution Characterization and Pathogenicity of a Porcine Reproductive and Respiratory Syndrome Virus Isolate from a Pig Farm in Shandong Province, China

In recent years, porcine reproductive and respiratory syndrome virus (PRRSV) strains have been experiencing extensive recombination in Chinese swine farms. This recombination usually happens in NADC30/34 strains and highly pathogenic (HP) PRRSV strains. This study identified a new PRRSV isolate that shared 99% and 99.1% nucleotide identity with CH-1a and CH-1R at the genomic level, respectively. After purification by viral plaque assay, this isolate was named PRRSV CSR1801. The isolate did not experience any recombination with other PRRSV strains common in swine herd epidemics in China, which means it still maintains the stable features of the classical PRRSV strain and did not easily recombine with other PRRSV strains. Further analysis of the pathogenicity of the PRRSV isolate CSR1801 was performed in piglets. The results indicated that none of the inoculated piglets showed the typical clinical manifestations of PRRS, which presented with runny noses, rough back hair, rectal temperatures always below 40.5 °C, and no deaths. Additionally, no obvious histopathological lesions such as severe interstitial pneumonia could be observed in the lungs of the piglets. Hence, the PRRSV isolate CSR1801 should be classified as a classical-like PRRSV strain. This classical PRRSV strain showed genetic stability and maintained low pathogenicity. This study may provide new clues for further understanding the genetic evolution and pathogenicity of PRRSV and may also be an important reference for the prevention and control of PRRS in swine farms.

Lineage 1 Porcine Reproductive and Respiratory Syndrome Virus Attenuated Live Vaccine Provides Broad Cross-Protection against Homologous and Heterologous NADC30-Like Virus Challenge in Piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that endangers the swine industry worldwide. Recently, lineage 1 PRRSVs, especially NADC30-like PRRSVs, have become the major endemic strains in many pig-breeding countries. Since 2016, NADC30-like PRRSV has become the predominant strain in China. Unfortunately, current commercial vaccines cannot provide sufficient protection against this strain. Here, an attenuated lineage 1 PRRSV strain, named SD-R, was obtained by passaging an NADC30-like PRRSV strain SD in Marc-145 cells for 125 passages. Four-week-old PRRSV-free piglets were vaccinated intramuscularly with 105.0TCID50 SD-R and then challenged intramuscularly (2 mL) and intranasally (2 mL) with homologous NADC30-like PRRSV SD (1 × 105.0TCID50/mL) and heterologous NADC30-like PRRSV HLJWK108-1711 (1 × 105.0TCID50/mL). The results showed that antibodies against specific PRRSVs in 5 of 5 immunized piglets were positive after a 14-day post-vaccination and did not develop fever or clinical diseases after NADC30-like PRRSV challenges. Additionally, compared with challenge control piglets, vaccinated piglets gained significantly more weight and showed much milder pathological lesions. Furthermore, the viral replication levels of the immunized group were significantly lower than those of the challenge control group. These results demonstrate that lineage 1 PRRSV SD-R is a good candidate for an efficacious vaccine, providing complete clinical protection for piglets against NADC30-like PRRSVs.

A rescued NADC30-like virus by reverse genetic manipulation exhibits moderate virulence and a promising application perspective

NADC30-like porcine reproductive and respiratory syndrome virus (PRRSV), which is highly homologous to the NADC30 strain isolated in the United States. The NADC30-like PRRSV was first reported in 2014 in China, where it spread and gradually caused an epidemic. Currently, growing research has shown that NADC30-like strains have greater propensity to recombine with other PRRSV strains, particularly the PPRSV vaccine virus used clinically, making the prevention and control of PRRSV highly complex. To carry out an in-depth molecular biology and virulence analysis, a full-length infectious clone of the NADC30-like strain was successfully constructed and rescued by reverse genetic manipulation. The rescued virus, rZJqz, was indistinguishable from its parental virus, ZJqz21, based on virological characteristics. Further animal experiments demonstrated that rZJqz retained similar pathogenicity and induced the typical clinical symptoms and viral shedding observed in the ZJqz21 challenge model. Together, these results provide a useful tool for further study of the biological characteristics and pathogenicity of NADC30-like strains. Moreover, these findings also provide a solid foundation for studying the recombination of different PRRSVs and developing new and effective universal vaccines in the future.

Epidemiological and Genetic Characteristics of Porcine Reproductive and Respiratory Syndrome Virus in South China Between 2017 and 2021

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major threat to the swine industry in China and has caused enormous losses every year. To monitor the epidemiological and genetic characteristics of PRRSV in South China, 6,795 clinical samples from diseased pigs were collected between 2017 and 2021, and 1,279 (18.82%) of them were positive for PRRSV by RT-PCR detecting the ORF5 gene. Phylogenetic analysis based on 479 ORF5 sequences revealed that a large proportion of them were highly-pathogenic PRRSVs (409, 85.39%) and PRRSV NADC30-like strains (66, 13.78%). Furthermore, 93.15% of these highly-pathogenic strains were found to be MLV-derived. We next recovered 11 PRRSV isolates from the positive samples and generated the whole genome sequences of them. Bioinformatic analysis showed that seven isolates were MLV-derived. Besides, six isolates were found to be recombinant strains. These eleven isolates contained different types of amino acid mutations in their GP5 and Nsp2 proteins compared to those of the PRRSVs with genome sequences publicly available in GenBank. Taken together, our findings contribute to understanding the prevalent status of PRRSV in South China and provide useful information for PRRS control especially the use of PRRSV MLV vaccines.

The Antiviral Effect of Isatis Root Polysaccharide against NADC30-like PRRSV by Transcriptome and Proteome Analysis

(1) Background: In recent years, the porcine reproductive and respiratory syndrome virus (PRRSV) has become a virulent pathogen that has caused devastating diseases and economic losses worldwide in the swine industry. IRPS has attracted extensive attention in the field of virology. However, it is not clear that IRPS has an antiviral effect on PRRSV at gene and protein levels. (2) Methods: We used transcriptomic and proteomic analysis to investigate the antiviral effect of IRPS against PRRSV. Additionally, a microbiome was used to explore the effects of IRPS on gut microbes. (3) Results: IRPS significantly extenuated the pulmonary pathological lesions and inflammatory response. We used transcriptomic and proteomic analysis to investigate the antiviral effect of IRPS against PRRSV. In the porcine model, 1669 differentially expressed genes (DEGs) and 370 differentially expressed proteins (DEPs) were identified. Analysis of the DEG/DEP-related pathways indicated immune-system and infectious-disease (viral) pathways, such as the NOD-like receptor (NLR) signaling pathway, toll-like receptor (TLR) signaling pathway, and Influenza A-associated signaling pathways. It is noteworthy that IRPS can inhibit NLR-dependent gene expression, then reduce the inflammatory damage. IRPS could exert beneficial effects on the host by regulating the structure of intestinal flora. (4) Conclusions: The antiviral effect of IRPS on PRRSV can be directly achieved by omics techniques. Specifically, the antiviral mechanism of IPRS can be better elucidated by screening target genes and proteins using transcriptome and proteome sequencing, and then performing enrichment and classification according to DEGs and DEPs.