Efficacy of a live attenuated highly pathogenic PRRSV vaccine against a NADC30-like strain challenge: implications for ADE of PRRSV

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.

Reverse genetics construction and pathogenicity of a novel recombinant NADC30-like PRRSV isolated in China

China has the largest pig herd in the world which accounts for more than 50% of the global pig population. Over the past three decades, the porcine reproductive and respiratory syndrome virus (PRRSV) has caused significant economic loss to the Chinese swine industry. Currently, the prevalent PRRSV strains in the field are extremely complicated, and the NADC30-like strains, NADC34-like strains, and novel recombinant viruses have become a great concern to PRRS control in China. In this study, a novel NADC30-like PRRSV, named GS2022, was isolated from the lung of a dead pig collected from a farm that experienced a PRRS outbreak. The complete genome of GS2022 shares the highest identity with the NADC30 strain and contains a discontinuous deletion of 131 aa in nsp2. Novel deletion and insertion have been identified in ORF7 and 3'UTR. Recombination analysis revealed that the GS2022 is a potential recombinant of NADC30-like and JXA1-like strains. Both inter-lineage and intra-lineage recombination events were predicted to be involved in the generation of the GS2022. An infectious cDNA clone of GS2022 was assembled to generate the isogenic GS2022 (rGS2022). The growth kinetics of rGS2022 were almost identical to those of GS2022. The pathogenicity of the GS2022 and rGS2022 was evaluated using a nursery piglet model. In the infection groups, the piglets exhibited mild clinical symptoms, including short periods of fever and respiratory diseases. Both gross lesions and histopathological lesions were observed in the lungs and lymph nodes of the infected piglets. Therefore, we reported a novel recombinant NADC30-like PRRSV strain with moderate pathogenicity in piglets. These results provide new information on the genomic characteristics and pathogenicity of the NADC30-like PRRSV in China.

Fidelity Characterization of Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus and NADC30-like Strain

The porcine reproductive and respiratory syndrome virus (PRRSV) has significantly impacted the global pork industry for over three decades. Its high mutation rates and frequent recombination greatly intensifies its epidemic and threat. To explore the fidelity characterization of Chinese highly pathogenic PRRSV JXwn06 and the NADC30-like strain CHsx1401, self-recombination and mutation in PAMs, MARC-145 cells, and pigs were assessed. In vitro, CHsx1401 displayed a higher frequency of recombination junctions and a greater diversity of junction types than JXwn06. In vivo, CHsx1401 exhibited fewer junction types yet maintained a higher junction frequency. Notably, JXwn06 showed more accumulation of mutations. To pinpoint the genomic regions influencing their fidelity, chimeric viruses were constructed, with the exchanged nsp9-10 regions between JXwn06 and CHsx1401. The SJn9n10 strain, which incorporates JXwn06's nsp9-10 into the CHsx1401 genome, demonstrated reduced sensitivity to nucleotide analogs compared to CHsx1401. Conversely, compared with JXwn06, the JSn9n10 strain showed increased sensitivity to these inhibitors. The swapped nsp9-10 also influences the junction frequency and accumulated mutations as their donor strains. The results indicate a propensity for different types of genetic variations between these two strains and further highlight the nsp9-10 region as a critical determinant of their fidelity.

Genomic similarity and antibody-dependent enhancement of immune serum potentially affect the protective efficacy of commercial MLV vaccines against NADC30-like PRRSV

Porcine reproductive and respiratory syndrome (PRRS) is one of the most significant diseases affecting the pig industry worldwide. The PRRSV mutation rate is the highest among the RNA viruses. To date, NADC30-like PRRSV and highly pathogenic PRRSV (HP-PRRSV) are the dominant epidemic strains in China; however, commercial vaccines do not always provide sufficient cross-protection, and the reasons for insufficient protection are unclear. This study isolated a wild-type NADC30-like PRRSV, SX-YL1806, from Shaanxi Province. Vaccination challenge experiments in piglets showed that commercial modified live virus (MLV) vaccines provided good protection against HP-PRRSV. However, it could not provide sufficient protection against the novel strain SX-YL1806. To explore the reasons for this phenomenon, we compared the genomic homology between the MLV strain and HP-PRRSV or NADC30-like PRRSV and found that the MLV strain had a lower genome similarity with NADC30-like PRRSV. Serum neutralization assay showed that MLV-immune serum slightly promoted the homologous HP-PRRSV replication and significantly promoted the heterologous NADC30-like PRRSV strain replication in vitro, suggesting that antibody-dependent enhancement (ADE) might also play a role in decreasing MLV protective efficacy. These findings expand our understanding of the potential factors affecting the protective effect of PRRSV MLV vaccines against the NADC30-like strains.

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.

Target Discovery of Matrine against PRRSV in Marc-145 Cells via Activity-Based Protein Profiling

Porcine reproductive and respiratory syndrome (PRRS) seriously endangers the sustainable development of the pig industry. Our previous studies have shown that matrine can resist porcine reproductive and respiratory syndrome virus (PRRSV) infection. This study aimed to explore the anti-PRRSV targets of matrine in Marc-145 cells. Biotin-labeled matrine 1 and 2 were used as probes. MTT assay was used to determine the maximum non-cytotoxic concentration (MNTC) of each probe in Marc-145 cells. The anti-PRRSV activity of each probe was evaluated via MTT, qPCR and Western blot, and its anti-inflammatory activity was evaluated via qPCR and Western blot. The targets of matrine in Marc-145 cells were searched using activity-based protein profiling (ABPP), and compared with the targets predicted via network pharmacology for screening the potential targets of matrine against PRRSV. The protein-protein interaction networks (PPI) of potential targets were constructed using a network database and GO/KEGG enrichment analysis was performed. ACAT1, ALB, HMOX1, HSPA8, HSP90AB1, PARP1 and STAT1 were identified as potential targets of matrine, and their functions were related to antiviral capacity and immunity. Matrine may play an anti-PRRSV role by directly acting on ACAT1, ALB, HMOX1, HSPA8, HSP90AB1, PARP1 and STAT1.

Antiviral and Immunomodulatory Activities of Clinacanthus nutans (Burm. f.) Lindau

Clinacanthus nutans (Burm. f.) Lindau has been used as a traditional herbal medicine for treating snake bites, scalds, burns, and viral and bacterial infections. It has been attracting an increasing amount of attention because of its biological activities, including its antidiabetic, antioxidant, antibacterial, anticancer, anti-inflammatory, antiviral, and immunoregulatory activities. Here, we conducted a panoramic survey of the literature regarding the immunoregulatory, anti-inflammatory, and antiviral activities of C. nutans. We discovered that C. nutans extracts have virucidal activities against herpes simplex virus types 1 and 2, varicella-zoster virus, cyprinid herpesvirus 3, porcine reproductive and respiratory syndrome virus, mosquito-borne chikungunya virus, and potentially SARS-CoV-2; such activities likely result from C. nutans interfering with the entry, penetration, infection, and replication of viruses. We also reviewed the phytochemicals in C. nutans extracts that exhibit anti-inflammatory and immunoregulatory activities. This updated review of the antiviral, anti-inflammatory, and immunoregulatory activities of C. nutans may guide future agricultural practices and reveal clinical applications of C. nutans.

Progress in PRRSV Infection and Adaptive Immune Response Mechanisms

Since its discovery, Porcine reproductive and respiratory syndrome (PRRS) has had a huge impact on the farming industry. The virus that causes PRRS is Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and because of its genetic diversity and the complexity of the immune response, the eradication of PRRS has been a challenge. To provide scientific references for PRRSV control and vaccine development, this study describes the processes of PRRSV-induced infection and escape, as well as the host adaptive immune response to PRRSV. It also discusses the relationship between PRRSV and the adaptive immune response.

Allicin Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection In Vitro and Alleviates Inflammatory Responses

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important pathogens to the swine industry worldwide over the past three decades. No approved effective antiviral drug is available to control this virus. The antiviral effects of allicin (diallyl thiosulfinate) on many human and animal viruses have been documented. However, the antiviral effect of allicin on PRRSV infection remains unknown. In this study, we found that allicin exhibited an inhibitory effect on HP-PRRSV and NADC30-like PRRSV in a dose-dependent manner by interfering with viral entry, replication, and assembly. Furthermore, allicin alleviated the expression of pro-inflammatory cytokines (IFN-β, IL-6, and TNFα) induced by PRRSV infection. The pro-inflammatory signaling pathways, TNF signaling pathway and MAPK signaling pathway, up-regulated by PRRSV infection were restored by allicin treatment. Taken together, these results demonstrate that allicin has antiviral activity against PRRSV and ameliorates inflammatory responses induced by PRRSV infection, suggesting that allicin is a promising drug candidate for anti-PRRSV therapy in vivo.

Synergistic pathogenicity by coinfection and sequential infection with JXA1-like HP-PRRSV and PCV2d in PCV2 antibody-positive post-weaned pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) and Porcine circovirus (PCV) are two important pathogens, which caused respiratory disease in pigs. PRRSV and PCV2 had caused great economic losses to the pig industry. Pigs coinfection with PCV2 and PRRSV were common in the clinic, PCV2 antibodies can be detected in most of the pigs. PCV2d and HP-PRRSV(JXA1-like) were two major viruses circulating in the pigs in China. In this study, HP-PRRSV (JXA1-like) and PCV2d were used to coinfect and (or) sequential infect 5-week-old weaned PCV2-antibody positive pigs and the clinical indications, pathological, virus load, and specific antibodies of the challenged post-weaned piglets were evaluated. Thirty 5-week-old post-weaned pigs were divided into six groups infected with PBS, PCV2, PRRSV, PCV2-PRRSV, PRRSV-PCV2, and Co-PRRSV-PCV2 according to the PCV2 specific antibodies. Pigs infected with PRRSV can experience diarrhea, increased body temperature, weight loss, and even death. The pigs in PRRSV and PRRSV-PCV2 infected groups showed severe clinical symptoms, high mortality, and low average daily gain. The main pathological changes were widening of the lung interstitium, lung adhesion, and so on. The PRRSV-PCV2-infected group showed high levels of TNF-α and IL-2. In conclusion, PRRSV and PRRSV-PCV2 sequential infected pigs showed most pathogenic signs, and PCV2-PRRSV sequential infected pigs showed less pathogenicity than pigs of PCV2 and PRRSV coinfection and PRRSV monoinfection from day 10-14, partially suppressing the cytokine storm produced by PRRSV.

A Recombinant Porcine Reproductive and Respiratory Syndrome Virus Stably Expressing a Gaussia Luciferase for Antiviral Drug Screening Assay and Luciferase-Based Neutralization Assay

The reverse genetics system is a valuable tool in the virological study of RNA viruses. With the availability of reverse genetics, the porcine reproductive and respiratory syndrome virus (PRRSV) has been utilized as a viral vector for the expression of foreign genes of interest. Here, we constructed a full-length cDNA clone of a highly pathogenic PRRSV (HP-PRRSV) TA-12 strain. Using this cDNA clone, we generated a reporter virus expressing a gaussia luciferase (Gluc) via an additional subgenomic RNA between ORF7 and 3′UTR. This reporter virus exhibited similar growth kinetics to the wild-type (WT) virus and remained genetically stable for at least ten passages in MARC-145 cells. In cells infected with this reporter virus, the correlation between the expression levels of Gluc in culture media and the virus titers suggested that Gluc is a good indicator of the reporter virus infection. With this reporter virus, we further established the Gluc readout-based assays for antiviral drug screening and serum neutralizing antibody detection that exhibited comparable performance to the classical assays. Taken together, we established a reverse genetics system of HP-PRRSV and generated a novel reporter virus that could serve as a valuable tool for antiviral drug screening and serum neutralizing antibody detection.

The Construction and Immunogenicity Analyses of Recombinant Pseudorabies Virus With NADC30-Like Porcine Reproductive and Respiratory Syndrome Virus-Like Particles Co-expression

Porcine reproductive and respiratory syndrome (PRRS) and pseudorabies (PR) are highly infectious swine diseases and cause significant financial loss in China. The respiratory system and reproductive system are the main target systems. Previous studies showed that the existing PR virus (PRV) and PRRS virus (PRRSV) commercial vaccines could not provide complete protection against PRV variant strains and NADC30-like PRRSV strains in China. In this study, the PRV variant strain XJ and NADC30-like PRRSV strain CHSCDJY-2019 are used as the parent for constructing a recombinant pseudorabies virus (rPRV)-NC56 with gE/gI/TK gene deletion and co-expressing NADC30-like PRRSV GP5 and M protein. The rPRV-NC56 proliferated stably in BHK-21 cells, and it could stably express GP5 and M protein. Due to the introduction of the self-cleaving 2A peptide, GP5 and M protein were able to express independently and form virus-like particles (VLPs) of PRRSV in rPRV-NC56-infected BHK-21 cells. The rPRV-NC56 is safe for use in mice; it can colonize and express the target protein in mouse lungs for a long time. Vaccination with rPRV-NC56 induces PRV and NADC30-like PRRSV specific humoral and cellular immune responses in mice, and protects 100% of mice from virulent PRV XJ strain. Furthermore, the virus-neutralizing antibody (VNA) elicited by rPRV-NC56 showed significantly lower titer against SCNJ-2016 (HP-PRRSV) than that against CHSCDJY-2019 (NADC30-like PRRSV). Thus, rPRV-NC56 appears to be a promising candidate vaccine against NADC30-like PRRSV and PRV for the control and eradication of the variant PRV and NADC30-like PRRSV.