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

Genetic evolution and alterations in pathogenicity of highly pathogenic porcine reproductive and respiratory syndrome virus

Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) and HP-PRRSV variant strains remain prevalent in China and Southeast Asian countries. However, their epidemiological aspects, genomic characteristics, relationships with vaccine strains, and changes in pathogenicity remain unclear. In this study, 2509 global L8.7 ORF5 sequences were utilized for analysis, we classified L8.7 into 7 groups (L8.7.1-L8.7.7). L8.7.1-L8.7.3 strains corresponded to previously reported classical PRRSVs, intermediate strains, and HP-PRRSVs, respectively, whereas L8.7.4-L8.7.7 were designated HP-like PRRSVs. Statistical analysis revealed that HP-like PRRSVs were the most prevalent among L8.7 strains, and L8.7.5 and L8.7.6 strains accounted for the highest proportions in recent years. A comprehensive analysis of the genome revealed that the majority (72.15%) of L8.7 strains presented a wild-type phenotype. Evolution rate analysis revealed that the evolution rate of L8.7.3-L8.7.7 PRRSV in China was reduced by about 4.1 times after the use of HP-PRRSV MLV. Pathogenicity test results indicate that in comparison with HP-PRRSV (L8.7.3: HuN4), the HP-like PRRSV strains (L8.7.5: DLF; L8.7.6: DLW) presented reduced pathogenicity in piglets while maintaining relatively high virulence. In summary, this study systematically elucidated the epidemiological dynamics, evolutionary trends, relationships with vaccine strains, and changes in pathogenicity associated with L8.7 strains, providing crucial data to support prevention and control strategies against L8.7 PRRSV.

Recombinant PRV Expressing GP3 and GP5 of PRRSV Provides Effective Protection Against Coinfection With PRV and PRRSV

Porcine Reproductive and Respiratory Syndrome (PRRS) and Pseudorabies (PR) are highly contagious diseases caused by Porcine Reproductive and Respiratory Syndrome virus (PRRSV) and Pseudorabies virus (PRV). Due to the limited protective ability of currently commercialized vaccines against NADC30-like PRRSV and PRV variants, the pathological damage caused by coinfection of these two viruses has a significant impact on China's pig farming industry. In this study, six recombinant PRV stains with TK and gI/gE deletions and fused expression of GM-CSF and GP3 and GP5 proteins from NADC30-Like PRRSV were constructed by using the HDR-CRISPR/Cas9D10A system. After assessing growth characteristics and genetic stability, four strains demonstrating stable proliferation and expression of the GM-CSF, GP3, GP5 fusion protein in BHK-21 cells were selected. Evaluation of their ability to induce specific humoral and cellular immune responses in mice led to the selection of two strains with superior immunogenic effects: rPRV-ΔTK-GP3-GP5-eGFP-ΔgI/gE-mCHERRY-B and rPRV-ΔTK-eGFP-ΔgI/gE-GP3-GP5-mCHERRY-B. These strains were found to enhance NADC30-like PRRSV and PRV-specific immune responses in piglets, reduce pathological damage, and accelerate symptom resolution. In general, PRV is a promising viral vector for expressing PRRSV genes, and the data from this study provides references for new candidate vaccines against PRRSV.

Role of Glycoprotein 3 in neutralizing antibody recognition of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has been causing significant economic losses in the global swine industry since its emergence. Insufficient knowledge of the structural glycoprotein characteristics of NADC30-like strains has hindered the development of effective control strategies. In this study, we found that the neutralizing antibodies (NAbs) in pig sera against NADC30-like PRRSV strain FJ1402 (lineage 1) and highly pathogenic PRRSV (HP-PRRSV) strain BB0907 (lineage 8) exhibited low cross-neutralizing activity against each other. Subsequently, six chimeric recombinant viruses were generated based on the infectious cDNA clone of HP-PRRSV strain BB0907, in which specific structural protein genes were replaced by those from the NADC30-like strain. Cross-neutralization assays revealed that the NAbs against NADC30-like strain primarily target glycoprotein 3 (GP3), glycoprotein 4 (GP4), and glycoprotein 5 (GP5). Furthermore, we constructed six additional infectious cDNA clones with point mutations in GP3, and found that the residues 66I and 85S in GP3 play critical roles during NAbs recognition. These findings provide molecular insights into the host neutralizing antibody recognition against PRRSV, highlighting the role of GP3 in the recognition process. This study offers a foundation for rational antigen selection strategies in developing PRRSV NADC30-like strain vaccines.

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

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

Antiviral mechanism of Fuzhengjiedu San against porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a viral infectious disease that can cause infection in pigs of different ages. The condition known as porcine reproductive and respiratory syndrome poses a serious risk to the world's pig business and results in significant financial losses. Fuzhengjiedu San (FZJDS) is a traditional Chinese medicine compound, the main components include:Radix Isatidis, Radix Astragali and Herba Epimedii. It has been widely used in clinical and experimental studies, showing a wide range of biological activity. However, it is not clear whether FZJDS has anti-PRRSV activity. We observed that FZJDS had significant antiviral activity in Marc-145 cells. And FZJDS could inhibit viral infection in the stages of viral internalization and replication. Furthermore, FZJDS can inhibit PRRSV replication by inhibiting the p53 signaling pathway to affect autophagy, and FZJDS can also inhibit PRRSV replication by inhibiting the PI3K/Akt pathway.We showed in this work that FZJDS inhibits PRRSV replication in vitro and offers a novel therapeutic approach for PRRSV infection.

PRRSV NSP1α degrades TRIM25 through proteasome system to inhibit host antiviral immune response

Porcine reproductive and respiratory syndrome (PRRS) is the most economically significant disease caused by porcine reproductive and respiratory syndrome virus (PRRSV). Type I interferon (IFN) induces a large number of interferon-stimulated genes (ISGs) expression to inhibit PRRSV infection. To survive in the host, PRRSV has evolved multiple strategies to antagonize host innate immune response. Previous studies have reported that PRRSV N protein decreases the expression of TRIM25 and TRIM25-mediated RIG-I ubiquitination to suppress IFN-β production. However, whether other PRRSV proteins inhibit the antiviral function of TRIM25 is less well understood. In this study, we first found that PRRSV NSP1α decreased ISGylation of TRIM25. Meanwhile, NSP1α significantly suppressed TRIM25-mediated IFN-β production to promote PRRSV replication. Further studies demonstrated that PRRSV NSP1α reduced the protein level of TRIM25 in proteasome system but did not regulate the transcription level of TRIM25. In addition, the function of NSP1α in TRIM25 degradation did not rely on its papain-like cysteine protease activity. Taken together, PRRSV NSP1α antagonizes the antiviral response of TRIM25 by mediating TRIM25 degradation to promote PRRSV replication. Our data identify TRIM25 as a natural target of PRRSV NSP1α and reveal a novel mechanism that PRRSV induces TRIM25 degradation and inhibits host antiviral immune response.

Isolation, identification, recombination analysis and pathogenicity experiment of a PRRSV recombinant strain in Sichuan Province, China

Since 2013, the porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2), lineage 1.8 (NADC30-like PRRSV) has emerged and become widely prevalent in China. The NADC30-like PRRSV poses significant challenges for disease control, primarily because of its propensity for frequent mutations and recombinations. We successfully isolated and identified a NADC30-like strain, designated SCCD22, in Chengdu, Sichuan Province, China. We meticulously examined the genetic recombination properties and evaluated its pathogenicity in 28-day-old piglets. SCCD22 showed 93.02% nucleotide homology with the NADC30 PRRSV strain, and its non-structural protein 2 coding region showed the same 131 amino acid deletion pattern as that seen in NADC30. Furthermore, we identified two recombination events in SCCD22: one in the NSP2 region (1,028-3,290 nt), where it was highly similar to the JXA1-like strain GZ106; and another in the NSP10 ~ 12 region (9,985-12,279 nt), closely resembling the NADC30-like strain CY2-1604. Piglets infected with SCCD22 exhibited clinical symptoms such as elevated body temperature, prolonged fever, reduced appetite, and roughened fur. Postmortem examinations underscored the typical lung pathology associated with PRRSV, indicating that the lungs were the primary affected organs. Furthermore, extended viral shedding accompanied by progressive viremia was observed in the serum and nasal excretions of infected piglets. In summary, this study reports a domestic PRRSV recombination strain in the Sichuan Province that can provide critical insights into preventing and controlling PRRSV in this region.