Pathogenicity and antigenicity of a novel NADC30-like strain of porcine reproductive and respiratory syndrome virus emerged in China

The GP2a 91/97/98 amino acid substitutions play critical roles in determining PRRSV tropism and infectivity but do not affect immune responses

Porcine reproductive and respiratory syndrome virus (PRRSV) isolates share a restricted cellular tropism. Marc-145 cells derived from African green monkey are one of the few cell lines supporting PRRSV propagation in vitro and are commonly used for PRRS vaccine development. However, currently prevalent PRRSV isolates display different Marc-145 cell tropism while the exact determinant is not clarified yet. In this study, we identified for the first time that the 91/97/98 amino acid (aa) substitutions in GP2a of PRRSV play critical roles in determining Marc-145 adaptation. Specifically, multiple series of chimeric viruses were constructed based on four PRRSV infectious clones including Marc-145 adaptive HP-PRRSV-2 strain and Marc-145 non-adaptive NADC34-like PRRSV-2, NADC30-like PRRSV-2, and PRRSV-1 strains. The GP2a 91/97/98 aa substitutions are a sufficient and necessary determinant in NADC34-like and NADC30-like PRRSV-2, a sufficient but not necessary determinant in HP-PRRSV-2, a necessary but not sufficient determinant in PRRSV-1, respectively. In addition, the GP2a substitutions also influenced PRRSV infectivity in PAMs and piglets. Noticeably, the GP2a substitutions did not significantly affect the levels of neutralizing antibodies, porcine T follicular helper (Tfh) cells, and PRRSV-specific IFNγ secreting cells. Overall, our results not only provide new insights into PRRSV tropism and infectivity but also will facilitate PRRS vaccine development.

IMPORTANCE

Prevalent PRRSV isolates present different cell tropisms in vitro. Clarifying the exact determinant of PRRSV tropism is crucial for PRRSV isolation and vaccine development. By constructing chimeric viruses based on four representative PRRSV infectious clones, we identified for the first time that the 91/97/98 amino acid substitutions in GP2a play critical but distinct roles in determining Marc-145 cell tropism for different PRRSV strains. The GP2a 91/97/98 amino acid substitutions also affect PRRSV infectivity in PAMs and piglets but do not influence immune responses. This study not only deciphers an exact determinant of PRRSV tropism and infectivity but also has guiding significance for PRRS vaccine development.

The NADC30-like PRRSV activates the integrin αV subunit to facilitate its entry into Marc-145 cells

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly contagious virus that poses a significant threat to the global pig farming industry, resulting in substantial economic losses. However, owing to the high variability of PRRSV and unclear mechanisms of infection, there are currently no effective vaccines or drugs available for its prevention and control. Our previous report revealed that highly pathogenic PRRSV (HP-PRRSV) requires the FAK-PI3K-AKT signaling pathway to facilitate its entry into cells. In this study, we further investigated whether the integrin subunit was involved in the entry process of NADC30-like PRRSV. First, the integrin subunits in Marc-145 cells were characterized by RT-PCR, and 11 of these subunits were identified, nearly all of which interacted with the integrin α V and β1 subunits to form heterodimers. Western blot analysis revealed that the integrin α V subunit was highly expressed in Marc-145 cells, and blocking this subunit with a functional antibody or siRNA significantly attenuated NADC30-like PRRSV entry without affecting virus binding. Moreover, in Marc-145 cells, NADC30-like PRRSV could activate the FAK-PI3K-AKT signaling pathway through the integrin α V subunit. Blocking the α V subunit significantly inhibited signal transduction and virus entry, and treatment of cells with the PI3K activator greatly reversed this inhibitory effect. Furthermore, the α V subunit activator manganese could also enhance NADC30-like PRRSV entry and signal transduction. In conclusion, our results revealed that NADC30-like PRRSV could activate the integrin α V subunit and subsequently transduce signals to the FAK-PI3K-AKT signaling pathway to facilitate entry into Marc-145 cells.

Development of SYBR green I-based real-time qPCR differential diagnosis assays for porcine reproductive and respiratory syndrome virus typing in Guangdong province

Introduction

Porcine Reproductive and Respiratory Syndrome (PRRS) is a highly contagious disease that causes reproductive disorders in sows and respiratory problems in pigs of different ages. It first appeared in the late 20th century in the United States and Europe before spreading globally, leading to significant economic losses in the swine industry. Porcine Reproductive and Respiratory Syndrome virus (PRRSV) has a high rate of genetic recombination, resulting in considerable genetic diversity within the virus. The lack of cross-protection between different lineages often leads to unsuccessful vaccination attempts.

Methods

To accurately distinguish PRRSV lineages and develop effective vaccination strategies for pigs, we have developed a fluorescence quantitative PCR (qPCR) method by designing specific primers and SYBR green dye. This method allows for the simultaneous identification of different PRRSV genotypes.

Results

Our experimental results show that these methods have good specificity and do not react with other common viral pathogens in pigs. This method also demonstrates good sensitivity, with the ability to detect low levels of the virus. The detection limits of these assay were 102 copies/μL for PRRSV-1 (European-type PRRS) and 101 copies/μL for PRRSV-2 (American-type PRRSV), HP-PRRSV (Highly Pathogenic PRRSV), and NL-PRRSV (NADC30-like PRRSV), respectively. Furthermore, the reproducibility of this method is commendable, with intra- and inter-assay coefficients of variation remaining below 3%. In the subsequent study, a total of 316 clinical samples of porcine with respiratory and reproductive failure symptoms were collected from 14 cities in Guangdong. The results showed that among these samples, 22.78% (72 out of 316) tested positive for PRRSV-2, 15.51% (49 out of 316) tested positive for HP-PRRSV, and 0.95% (3 out of 316) tested positive for NL-PRRSV. However, PRRSV-1 was not detected in any of the samples.

Discussion

Our method provides a quick way to identify PRRSV genotypes in pig herds in Guangdong, which has certain significance for developing effective vaccination strategies against PRRS.

Recombination and pathogenicity analysis of NADC30-like and QYYZ-like PRRSV strains in South China

Since 2010, the Lineage 1 (NADC30-like) and Lineage 3 (QYYZ-like) strains of PRRSV-2 have become widespread in China, undergoing recombination and resulting in varying virulent and immune-evading mutants that have severely impacted the pig farming industry. In this study, we isolated one NADC30-like strain (GXHX20211106) and one QYYZ-like strain (GXGG202007) from pig serum samples collected in southern China. Comparative genomic analysis revealed that GXHX20211106 shares 90 % identity with NADC30, while GXGG202007 shows 91.4 % similarity to QYYZ. Both strains exhibit characteristic amino acids deletions or insertions in the Nsp2 region. Phylogenetic analyses further classified GXHX20211106 within Lineage 1.8 (NADC30-like) and GXGG202007 in Lineage 3 (QYYZ-like). Recombination analysis demonstrated that GXHX20211106 resulted from recombination between NADC30-like and HP-PRRSV-like strains, while GXGG202007 originated from recombination events involving QYYZ-like, VR-2332-like, and HP-PRRSV-like strains. Pathogenicity studies in piglets indicated that both isolates caused moderate clinical signs, with GXHX20211106 showing higher virulence compared to GXGG202007. No deaths were recorded in the infected piglets. These findings highlight the critical role of recombination in shaping PRRSV virulence and underscore the need for ongoing surveillance and control measures to mitigate the impact of recombinant PRRSV strains in southern China.

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.

Recombinant characteristics and pathogenicity of a novel PRRSV variant in weaned piglets derived from recombination of three clinical epidemic strains

Introduction

The recent emergence of PRRSV strains NADC30 and NADC34, along with their recombination with HP-PRRSV-like strains, has added complexity to PRRS control strategies on swine farms. Given the high variability and recombination potential of PRRSV, continuous monitoring of the virus's clinical epidemiology is essential for effective prevention and control.

Methods

This study isolated a PRRSV variant, designated SDVD-NMG2023, from approximately 65-day-old pigs, showing a mortality rate of around 15% within the herd. The whole-genome, ORF5, and NSP2 sequences of the SDVD-NMG2023 isolate were aligned with 42 reference strains using MEGA software. Recombination analysis was performed using SimPlot software and RDP software. Pathogenicity analysis of SDVD-NMG2023 was conducted in four-week-old SPF Yorkshire piglets.

Results

Phylogenetic and molecular evolutionary analyses revealed a natural recombination event involving the NADC30, NADC34, and JXA1 strains. Piglets infected with SDVD-NMG2023 exhibited mild clinical symptoms, including elevated rectal temperatures in two out of five piglets, as well as cough, mild anorexia, weight stunting, interstitial pneumonia, and thymic atrophy in all cases.

Discussion

The findings indicate that the novel crossbred PRRSV isolate SDVD-NMG2023, derived from three prevalent clinical strains, may induce more unusual clinical presentations compared to those associated with HP-PRRS, albeit still impacting the health of the herd by causing immunosuppression. This study provides critical insights into the emergence of multi-strain PRRSV recombination, particularly between NADC30/34-like and HP-PRRSV-like strains, supporting a more strategic and comprehensive approach to PRRS prevention and control.

Evaluation of the cross-protective effect of VR2332 modified live virus vaccine against a recombinant NADC34-like porcine reproductive and respiratory syndrome virus

In recent years, NADC34-like strains of porcine reproductive and respiratory syndrome virus have gradually emerged as mainstream strains on Chinese pig farms. These strains have high mutation rates and can recombine with local strains, representing great challenges to prevention and control efforts. Previously, a new recombinant NADC34-like subtype strain was isolated in our laboratory. Herein, we evaluated the cross-protective effect of the VR2332 modified live virus (MLV) against the novel NADC34-like recombinant strain using the immune challenge protection test in piglets and sows. The results revealed that immunization with the vaccine in piglets significantly reduced viremia, lung damage and stimulated the production of PRRSV-N antibodies. In the sow challenge experiment, one abortion and one death were recorded in the positive control group, and the survival rate of offspring was only 25%. However, there were no sow deaths or abortions in the immunization group during the experiment, and the average piglet survival rate was high at 76.5%. In general, the VR2332 MLV confers a certain extent of cross-protection against the NADC34-like recombinant strain, providing an effective reference and guidance for prevention and control efforts and clinical vaccine use.

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

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

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

IMPORTANCE

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS AND RELEVANCE

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

Molecular detection and genetic characteristics of porcine reproductive and respiratory syndrome virus in central China

Porcine reproductive and respiratory syndrome caused by porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically devastating viral diseases in the global pork industry. To further clarify the epidemic characteristics of the virus, 365 clinical samples were collected from diseased pigs suffering from abortion and respiratory disease from 2018 to 2023 on 63 pig farms in Henan and Shanxi provinces, and screened for the presence of PRRSV using reverse transcription-polymerase chain reaction (RT-PCR). A total of 62 clinical samples (62/365, 16.99 %) were positive for PRRSV, and subsequently, full-length ORF5 gene sequences of 29 PRRSV strains and the complete genome sequence of one PRRSV HeN-HC isolate were obtained and analyzed. Phylogenetic analysis based on the ORF5 gene showed that 22 of the 29 PRRSV2 strains belonged to sublineage 1.8 (NADC30-like), 5 belonged to sublineage 8.5 (HP-PRRSV), and 2 belonged to sublineage 5.1 (VR-2332-like), indicating that both HP-PRRSV and NADC30-like strains were mainly circulating in Henan and Shanxi provinces. Compared to VR-2332 strain, different types of amino acid mutations were found in the GP5 protein of these 29 strains, and the amino acid deletions were displayed in the Nsp2 protein of the HeN-HC isolate, leading to the variation of protein structures. It is noteworthy that recombination events were identified in the HeN-Ping and HeN-B strains. In addition, a total of 60, 094 pig serum samples from Henan province were collected, and the positive rate of specific antibodies against PRRSV was 86.37 % from 2019 to 2022, and 86.66 %, 84.85 %, 87.54 % and 86.30 % in 2019, 2020, 2021 and 2022, respectively. Overall, this study provides valuable insights into the molecular epidemiology and evolution of PRRSV circulating in central China.

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.

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.

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.

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.

Prevalence and genetic evolution of porcine reproductive and respiratory syndrome virus in commercial fattening pig farms in China

BACKGROUND

To investigate the prevalence and evolution of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) at commercial fattening pig farms, a total of 1397 clinical samples were collected from a single fattening cycle at seven pig farms in five provinces of China from 2020 to 2021.

RESULTS

The RT‒PCR results revealed that PRRSV was present on all seven farms, and the percentage of PRRSV-positive individuals was 17.54-53.33%. A total of 344 partial NSP2 gene sequences and 334 complete ORF5 gene sequences were obtained from the positive samples. The statistical results showed that PRRSV-2 was present on all seven commercial fattening farms, and PRRSV-1 was present on only one commercial fattening farm. A total of six PRRSV-2 subtypes were detected, and five of the seven farms had two or more PRRSV-2 subtypes. L1.8 (L1C) PRRSV was the dominant epidemic strain on five of the seven pig farms. Sequence analysis of L1.8 (L1C) PRRSV from different commercial fattening pig farms revealed that its consistency across farms varied substantially. The amino acid alignment results demonstrated that there were 131 aa discontinuous deletions in NSP2 between different L1.8 (L1C) PRRSV strains and that the GP5 mutation in L1.8 (L1C) PRRSV was mainly concentrated in the peptide signal region and T-cell epitopes. Selection pressure analysis of GP5 revealed that the use of the PRRSV MLV vaccine had no significant episodic diversifying effect on L1.8 (L1C) PRRSV.

CONCLUSION

PRRSV infection is common at commercial fattening pig farms in China, and the percentage of positive individuals is high. There are multiple PRRSV subtypes of infection at commercial fattening pig farms in China. L1.8 (L1C) is the main circulating PRRSV strain on commercial fattening pig farms. L1.8 (L1C) PRRSV detected at different commercial fattening pig farms exhibited substantial differences in consistency but similar molecular characteristics. The pressure on the GP5 of L1.8 (L1C) PRRSV may not be directly related to the use of the vaccines.

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.

Protective Efficacy of a Candidate Live-Attenuated Vaccine Derived from the SD-R Strain against NADC34-like Porcine Reproductive and Respiratory Syndrome Virus

NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV) strains were first detected in China in 2017 and became major circulating strains in 2021. Our previous study showed that the live-attenuated vaccine candidate SD-R strain could provide broad cross-protection against different NADC30-like PRRSVs (sublineage 1.8). However, the protective effect of SD-R against NADC34-like PRRSV is unclear. Here, a novel NADC34-like PRRSV, LNTZJ1341-2012, was isolated from a pig farm experiencing disease in 2020. Sequence analysis revealed that LNTZJ1341-2012 belonged to PRRSV-2 sublineage 1.5, exhibited the same Nsp2 amino-acid deletion characteristics as IA/2014/NADC34, and had not recombined with other strains. Additionally, a good challenge model was established to evaluate the protection afforded by the candidate SD-R vaccine against infection with a representative NADC34-like strain (LNTZJ1341-2012). The control piglets in the challenge experiment displayed clinical signs typical of PRRSV infection, including transient fever, high viremia, mild clinical symptoms, and histopathological changes in the lungs and submaxillary lymph nodes. In contrast, SD-R vaccination significantly reduced serum and lung tissue viral loads, and vaccinated piglets did not show any clinical symptoms or histopathological changes. Our results demonstrated that LNTZJ1341-2012 is a mildly virulent NADC34-like PRRSV and that the live-attenuated vaccine SD-R can prevent the onset of clinical signs upon challenge with the NADC34-like PRRSV LNTZJ1341-2012 strain, indicating that SD-R is a promising vaccine candidate for the swine industry.

Genetic Characteristics of Three Single-Farm-Isolated Porcine Reproductive and Respiratory Syndrome Viruses with Novel Recombination among NADC30-Like, JXA1-Like, and QYYZ-Like Strains

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically devastating pathogenic microorganism that greatly affects the pork industry in the world. The genetic variation and frequent emergence of novel strains greatly hinder the control efforts of PRRSV. Therefore, monitoring the evolutionary dynamics is long and rewarding work for PRRSV researchers and practitioners to make the control strategy. Here, three novel PRRSV strains named CHbj2101, CHbj2102, and CHbj2103 were isolated from different nursery barns with various mortality rates from 6% to 17%, belonging to the same farm, but at different periods of the outbreak. The genomic sequencing and phylogenetic analyses indicated that these three isolates were all clustered with NADC30-like virus CHsx1401, sharing higher genomic similarity from 87.3% to 89.8%, and having the same molecular marker of 131 amino acid residues deletion at their nsp2 coding region, but varied mutagenesis among the antigenic sites in the region of GP2 to GP5. Among the available PRRSV sequences in the GenBank, the isolates CHbj2101 and CHbj2102 display the highest genomic identity (90.1% and 89.8%) with NADC30-like recombinant strain 15LN3, and the rest CHbj2103 shows the highest genomic identity (90.8%) with NADC30-like virus strain 15SC3. The recombination analysis indicated that all three isolates are generated by multiple recombination events among the NADC30-like virus (major parent, Lineage 1), HP-PRRSV vaccine-like virus (minor parent, Lineage 8), and QYYZ-like virus (minor parent, Lineage 3). The isolates CHbj2101 and CHbj2102 shared a similar recombination pattern, but CHbj2103 has a different pattern in nonstructural protein coding regions. To further investigate the recombination characteristics of QYYZ-like strains, we analyzed all available whole genomic sequences of QYYZ-like PRRSV, submitted during the year 1991 and 2021 (n = 83) in China. The result shows that almost all QYYZ-like strains were products of recombination and their immunogenicity or protective protein fragments (nsp2-nsp7 and GP2-GP4) were mainly from QYYZ. These results provide us with some better insight into the evolution process of PRRSV strains in the field and warn us to pay more attention to monitoring and reducing the PRRSV variant on farms to reduce the risk of novel emergence and outbreak.

A potent CD8 T-cell response may be associated with partial cross-protection conferred by an attenuated Chinese HP-PRRSV vaccine against NADC30-like PRRSV challenge

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most devastating pathogens to the global swine industry. Many commercial PRRSV vaccines, originally designed to provide homologous protection, have shown partial protection against heterologous strains. However, the protective immune mechanisms mediated by these PRRSV vaccines are not fully understood. In this study, we investigated the factors responsible for partial protection conferred by an attenuated Chinese HP-PRRSV vaccine (TJM-F92) against heterologous NADC30-like PRRSV. By analysing peripheral T-cell responses induced by the TJM-F92 vaccine and local and systemic memory responses following challenge with NADC30-like PRRSV (SD17-38 strains) as well as neutralizing antibody response, we found that the TJM-F92 vaccine induced a significant expansion of CD8 T cells but not CD4 T cells or γδ T cells. The expanded CD8 T cells exhibited a phenotype of effector memory T cells and secreted IFN-γ upon restimulation with SD17-38 strains in vitro. In addition, only CD8 T cells in the prior immunized pigs rapidly expanded in the blood and spleen after heterologous challenge, with higher magnitude, compared to the unvaccinated pigs, showing a remarkable memory response. In contrast, no obvious humoral immune response was enhanced in the vaccinated and challenged pigs, and no heterologous neutralizing antibodies were detected throughout the experiment. Our results suggested that CD8 T cells elicited by the TJM-F92 vaccine may be responsible for partial heterologous protection against NADC30-like PRRSV strains and potentially recognize the conserved antigens among PRRSV strains.

A novel NADC34-like porcine reproductive and respiratory syndrome virus 2 with complex genome recombination is highly pathogenic to piglets

The NADC34-like porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) first emerged in China in 2017 and has the potential to become the dominant PRRSV strain in China. Here, a novel PRRSV-2, SCcd2020, was isolated from diseased piglets in Sichuan province, southwest China in 2020. The complete viral genome was determined and analyzed. An ORF5-based phylogenetic analysis showed that SCcd2020 clustered with NADC34-like strains, whereas the genome sequence clustered the isolate with NADC30-like viruses and it contains a discontinuous 131-aa deletion in NSP2 when compared to NADC30 strain. Notably, recombination analyses indicated that SCcd2020 is a multiple recombinant virus from NADC30-like, NADC34-like and JXA1-like strains, which is the first description of Chinese domestic HP-PRRSV involving the recombination event of an NADC34-like strain. Importantly, an animal challenge study in 4-week-old piglets showed that SCcd2020 causes high fever and severe hemorrhagic pneumonia with pulmonary consolidation and edema, and it has a high mortality rate (60%), which indicated that SCcd2020 is a highly pathogenic PRRSV strain. The study reports the emergence of a novel highly pathogenic NADC34-like recombinant strain, and it highlights the importance of monitoring newly emerging PRRSV strains in China.

Glycosylated protein 4-deficient PRRSV in complementing cell line shows low virus titer

Porcine Reproductive and Respiratory Syndrome (PRRS) threats the swine industry seriously. The spread of live vaccine virus leads to the emergence of recombinant virus, which brings biosafety problems. The replication-deficient virus as a vaccine candidate would avoid this problem. In the present study, the recombinant lentiviral plasmid pLV-EF1α-EGFP-2A-ORF4 was co-transfected with lentivirus in HEK293FT cells. The transfection mixture was harvested and transduced into Marc-145 to screen a cell line stably expressing the PRRSV ORF4 with puromycin. The cell line Marc-145-GP4 was confirmed with PCR, RT-PCR, IFA, and Western blotting using a monoclonal antibody against Glycoprotein 4 (GP4) of PRRSV. To obtain a replication-deficient PRRSV, Western blotting the recombinant plasmid pNM09-ΔORF4 was constructed by Overlap PCR and DNA recombinant technology with the pNM09 as a backbone plasmid. The pNM09-ΔORF4 was transfected into Marc-145-GP4 with electroporation after transcription in vitro. The replication-deficient virus was rescued on Marc-145-GP4 cells with trans-complementation of ORF4 gene and verified by RT-PCR and IFA. The results indicated that a cell line Marc-145-GP4 stably expressed PRRSV ORF4 was obtained. The recombinant GP4 was successfully expressed and obtained a monoclonal antibody Anti-A-GP4-70, which can specifically react with the virus. Finally, the replication-deficient virus rNM09-ΔORF4 can be rescued with low titer and could only reproduce on the Marc-145-GP4 cells. Unfortunately, the rNM09-ΔORF4 showed too low virus replication titer to determine it. This study lays the foundation for the rapid detection of PRRS and the functional study of GP4 and provides experience for replication-deficient PRRSV.

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.

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.

Characterization of a new NSP2-deletion NADC34-Like Porcine Reproductive and Respiratory Syndrome Virus in China

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is the causative agent of Porcine Reproductive and Respiratory Syndrome (PRRS), which has caused huge economic losses to the pig industry worldwide. PRRSV NADC34-Like PRRSV 2020-Acheng-1 strain, which caused high morbidity and high mortality were isolated from dead piglets (high-throughput sequencing to show that only PRRSV and TGEV) on a farm in northeastern China. The full-length genome sequence of 2020-Acheng-1 shares 95.6% nucleotide homology with NADC34 PRRSV without any gene insertion, but has a unique 17 amino acid (469aa to 486aa) deletion in Nsp2 compared with all NADC34-Like strains in NCBI and there are unique 100 amino acid deletions. In addition, difference degree of changes in signal peptide, trans-membrane region (TM), main neutralizing epitope (PNE), non-neutralizing epitope and N-glycosylation site were observed in GP5 of 2020-Acheng-1 and other PRRSV-2 strains, we only found a change in the fifteenth amino acid of signal peptide of in GP5 of 2020-Acheng-1 with NADC34 strains. Recombination analysis showed that 2020-Acheng-1 strain did not have any recombination events with representative PRRSV-2 strains in China. This study provided valuable evidence for understanding the role of NADC34-Like strain that impact on pathogenicity.

The Emergence and Pathogenesis of Recombinant Viruses Associated with NADC34-like Strains and the Predominant Circulating Strains of Porcine Reproductive and Respiratory Syndrome Virus in Southern China

Since its recent appearance in China, the NADC30-like strains of porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) have caused an expanding epidemic, and this has further expanded the genetic diversity of PRRSV. In this study, three NADC30-like strains—GXFCG20210401, GXQZ20210403 and GXNN20210506—were isolated from pig serum samples obtained in Guangxi, and their genomes were sequenced. A comparative analysis of the whole genomes showed that the three strains were most similar to NADC30 (88.3–88.7%). In particular, the non-structural protein coding regions (nsp1, nsp4-5, nsp7-8 and nsp9) showed the highest similarities to JXA1, and the ORF2a-ORF5 regions showed the highest similarities to NADC34. The three strains had same discontinuous deletions of 111+1+19 amino acids in the nsp2 region, which were similar to the NADC30-like strains. Phylogenetic tree analysis based on the ORF5 gene showed that the three PRRSV isolates were divided into lineage 1.5 along with the representative NADC34-like strains, but they were classified as NADC30-like strains with respect to the whole genome and nsp2 evolutionary trees. Recombinant analysis revealed complex recombination patterns in the genomes of the three strains, which likely originated from multiple recombination events among JXA1-like, NADC30-like and NADC34-like strains. The results from animal experiments showed that the GXQZ20210403 strain was 20% lethal to piglets and caused more severe clinical reactions than GXFCG20210401, and both recombinant strains were similar in terms of pathogenicity to the previously reported NADC34 strains. This study demonstrates that NADC34-like strains of PRRSV have been circulating in the southern provinces of China and have exchanged genomes with several other indigenous strains. In addition, differences in recombination patterns may cause different clinical pathogenicity and indicate the importance of the surveillance and preventive control of recombinant strains.

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 (<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.

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.

First study on genetic variability of bovine viral diarrhea virus isolated from Sapera dairy goats with reproductive disorders in Yogyakarta, Indonesia

Background and Aim

Bovine viral diarrhea (BVD) virus (BVDV) is an important viral pathogen of cattle that can infect diverse artiodactyl species. The clinical manifestations caused by BVDV in heterologous hosts, as they do in cattle, vary, although respiratory and reproductive failures are commonly reported. BVDV infections commonly result in reproductive failure in goats, with abortion being the primary clinical sign. In central Java, Indonesia, BVDV infection has been reported in two clinically healthy local goat species, and the testing indicated infection by BVDV Type 1. However, the genetic diversity of viruses has not been described in healthy or ill goats. The objectives of the present study were as follows: (1) To investigate the genetic variation of BVDV isolated from Sapera dairy goats with naturally occurring reproductive disorders in Yogyakarta, Indonesia, using the 5' untranslated region (5' UTR) and (2) to study the possible correlation between reproductive disorders and the presence of BVDV in the flock.

Materials and Methods

Blood samples were collected in October 2021 from 39 goats that had been individually reported to have reproductive disorders. The serum samples were subjected to molecular detection and genetic characterization of BVDV based on the 5' UTR of the viral genome, followed by sequencing and phylogenetic analyses. Viral isolation was performed on BVDV-positive samples to analyze the viral biotypes.

Results

BVDV infection was detected in five out of 39 female goats. The clinical status of the BVDV-infected goats was abortion (n=2), metritis (n=1), and repeated breeding (n=2). All antigen-positive samples were confirmed as BVDV type 1a (BVDV-1a) and noncytopathic (NCP)-BVDV biotype.

Conclusion

The BVDV-1a and NCP biotypes are the main subtypes and biotypes present in Sapera dairy goats exhibiting reproductive failure. This result is consistent with previous results in dairy cattle in Yogyakarta. The reported results can facilitate the design of methods for the prevention and control of BVD circulating in Indonesia.

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.

Genetic characterization and pathogenicity of a novel recombinant PRRSV from lineage 1, 8 and 3 in China failed to infect MARC-145 cells

The diversity of porcine reproductive and respiratory syndrome virus (PRRSV) in China is increasing rapidly along with mutation and recombination. Recombination could occur between inter- and intra-lineage of PRRSV, which accelerated the complexity of pathogenicity and cell tropism of the recombinant strain. In the present study, a novel PRRSV strain named HN-YL1711 was isolated from a pig farm suffering from severe respiratory difficulty in Henan province, China. The whole genomic sequence analysis indicated that the genome of HN-YL1711 was 15018 nt. It shared 86%, 87.3%, 88.1%, 91.1%, 84.2%, and 84.1% nucleotide similarities with PRRSVs VR2332, CH1a, JXA1, NADC30, QYYZ, and GM2, respectively. Based on phylogenetic analysis of Nsp2, ORF5 and complete genomes, HN-YL1711 was classified into lineage 1 of PRRSV. However, seven genomic break points were detected in recombination analysis, which indicated that the HN-YL1711 originated from multiple recombination among NADC30-like (major parent, lineage 1), JXA1-like (minor parent, lineage 8), and QYYZ-like (minor parent, lineage 3) PRRSV. Porcine alveolar macrophages (PAMs), 3D4/21-CD163 and MARC-145 cells were used to explore the viral adaptation of HN-YL1711. The results indicated that it could infect the PAMs but failed to infect MARC-145 cells. Challenge experiments showed that HN-YL1711 exhibits intermediate virulence in pigs, compared with HP-PRRSV JXA1 and LP-PRRSV CH1a. Taken together, our findings suggest that recombination remains an important factor in PRRSV evolution and that recombination further complicates the cell tropism and pathogenicity of PRRSV.

Recombinant Bivalent Live Vectored Vaccine Against Classical Swine Fever and HP-PRRS Revealed Adequate Heterogeneous Protection Against NADC30-Like Strain

The recombinant bivalent live vectored vaccine rPRRSV-E2 has been proved to be a favorable genetic engineering vaccine against classical swine fever (CSF) and highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS). NADC30-like strains have recently emerged in China and caused severe disease, and it is necessary to evaluate the vaccine candidate for the currently circulating viruses. This study established a good challenge model to evaluate the candidate rPRRSV-E2 vaccine in preventing infection with a representative NADC30-like strain (ZJqz21). It was shown that the challenge control piglets displayed clinical signs typical of PRRSV, including a persistent fever, dyspnea, moderate interstitial pneumonia, lymph node congestion, and viremia. In contrast, the rPRRSV-E2 vaccination significantly alleviated the clinical signs, yielded a high level of antibodies, provided adequate protection against challenge with ZJqz21, and inhibited viral shedding and the viral load in target tissues. Our results demonstrated that the recombinant bivalent live vectored vaccine strain rPRRSV-E2 can provide efficient protection against the challenge of heterologous circulating NADC30-like strain and could be a promising vaccine candidate for the swine industry.

Synergistic Pathogenicity by Coinfection and Sequential Infection with NADC30-like PRRSV and PCV2 in Post-Weaned Pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus (PCVs) are two major viruses that affect pigs. Coinfections between PRRSV and PCV2 are frequently reported in most outbreaks, with clinical presentations involving dyspnea, fever, reduced feed intake, weight loss, and death in fattening pigs. The NADC30-like PRRSV and PCV2d are the main circulating virus strains found in China. This study determines the impact of NADC30-like PRRSV and PCV2d mono-infection and coinfection on the immune system, organ pathology, and viral shedding in five-week-old post-weaned pigs. Pigs were randomly divided into six groups: PBS, PRRSV, PCV2, PRRSV-PCV2 coinfection (co), and PRRSV-PCV2 or PCV2-PRRSV sequential infections. Fever, dyspnea, decreased feed intake, weight loss, and pig deaths occurred in groups infected with PRRSV, Co-PRRSV-PCV2, and PRRSV-PCV2. The viral load was higher in Co-PRRSV-PCV2, PRRSV-PCV2, and PCV2-PRRSV than those mono-infected with PRRSV or PCV2. Additionally, cytokines (IFN-γ, TNF-α, IL-4, and IL-10) produced by pigs under Co-PRRSV-PCV2 and PRRSV-PCV2 groups were more intense than the other groups. Necropsy findings showed hemorrhage, emphysema, and pulmonary adhesions in the lungs of pigs infected with PRRSV. Smaller alveoli and widened lung interstitium were found in the Co-PRRSV-PCV2 and PRRSV-PCV2 groups. In conclusion, PRRSV and PCV2 coinfection and sequential infection significantly increased viral pathogenicity and cytokine responses, resulting in severe clinical signs, lung pathology, and death.

The Novel PRRSV Strain HBap4-2018 with a Unique Recombinant Pattern Is Highly Pathogenic to Piglets

Currently, various porcine reproductive and respiratory syndrome virus (PRRSV) variants emerged worldwide with different genetic characteristics and pathogenicity, increasing the difficulty of PRRS control. In this study, a PRRSV strain named HBap4-2018 was isolated from swine herds suffering severe respiratory disease with high morbidity in Hebei Province of China in 2018. The genome of HBap4-2018 is 15,003 nucleotides in length, and compared with NADC30-like PRRSV, nsp2 of HBap4-2018 has an additional continuous deletion of five amino acids. Phylogenetic analysis based on complete genome and ORF5 showed that HBap4-2018 belonged to lineage 8 of PRRSV-2, which was characterized by highly variable genome. However, HBap4-2018 was classified into lineage 1 based on phylogenetic analysis of nsp2, sharing higher amino acid homology (85.3%-85.5%) with NADC30-like PRRSV. Further analysis suggested that HBap4-2018 was a novel natural recombinant PRRSV with three recombinant fragments in the genome, of which highly pathogenic PRRSV (HP-PRRSV) served as the major parental strains, while NADC30-like PRRSV served as the minor parental strains. Five recombination break points were identified in nsp2, nsp3, nsp5, nsp9 and ORF6, respectively, presenting a novel recombinant pattern in the genome. Piglets inoculated with HBap4-2018 presented typical clinical signs with a mortality rate of 60%. High levels of viremia and obvious macroscopic and histopathological lesions in the lungs were observed, revealing the high pathogenicity of HBap4-2018 in piglets.

Advanced Research in Porcine Reproductive and Respiratory Syndrome Virus Co-infection With Other Pathogens in Swine

The porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen causing epidemics of porcine reproductive and respiratory syndrome (PRRS), and is present in every major swine-farming country in the world. Previous studies have demonstrated that PRRSV infection leads to a range of consequences, such as persistent infection, secondary infection, and co-infection, and is common among pigs in the field. In recent years, coinfection of PRRSV and other porcine pathogens has occurred often, making it more difficult to define and diagnose PRRSV-related diseases. The study of coinfections may be extremely suitable for the current prevention and control in the field. However, there is a limited understanding of coinfection. Therefore, in this review, we have focused on the epidemiology of PRRSV coinfection with other pathogens in swine, both in vivo and in vitro.

Epidemiology investigation of PRRSV discharged by faecal and genetic variation of ORF5

To obtain more information of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) transmission via faeces in/between farms, 360 swine faecal samples were randomly collected from different farms in China from 2017 to 2019. Sixty-two ORF5 genes were amplified by PCR from 120 positive samples identified by real-time RT-PCR and further characterized by sequencing. Phylogenetic analysis based on the ORF5 gene revealed that these strains can be divided into four lineages: lineage 1 (NADC30-like), lineage 3 (QYYZ-like), lineage 5.1 (VR2332-like) and lineage 8.7 (JXA1-like), with 62.9% (39/62) NADC30-like virus, 21% (13/62) QYYZ-like virus, 1.6% (1/62) VR2332-like virus and 14.5% (9/62) for JAX1-like virus. In particular, 14 PRRSVs including lineage 1, 5.1 and 8.7 can be isolated from 120 positive faecal samples, which further suggests that faecal transmission may be an important factor in the spread of PRRSV in farms. Full-length genome sequencing analysis showed that 14 isolates share 83.1%-97.7% homology with each other and 82.3%-96.1% identity with NADC30, 83.2%-99.7% with VR2332, 79.6%-87.2% with QYYZ and 82.6%-98.9% with JXA1 and CH-1a, and only 60.1%-60.7% with LV. Recombination events were observed in the six out of 14 strains. Collectively, the data of this study are useful for understanding the spread of PRRSV via faeces. Additionally, the virus was isolated from positive faecal samples, suggesting that faecal transmission may be an important factor in the spread of PRRSV in farms.

The emergence of a novel recombinant porcine reproductive and respiratory syndrome virus with an amino acid insertion in GP5 protein

As an economic devastating virus, porcine reproductive and respiratory syndrome virus (PRRSV) has spread globally, and seriously hinders the healthy development of the swine industry worldwide. In recent years, however, recombinant PRRSV strains are continuously emerging, resulting in the death of a large number of pigs in China. In this study, we reported a NADC30-like PRRSV strain GD1909, a recombinant virus, which may originate from NADC30-like and HUN4-like strains. The GP5 protein of GD1909 strain has an asparagine insertion at position 60 and has more complex glycosylation pattern. This should be helpful for a better understanding of PRRSV molecular epidemiology and the prevention of PRRSV infection in the future.

Porcine reproductive and respiratory syndrome virus Nsp4 cleaves ZAP to antagonize its antiviral activity

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important pathogens impacting the global swine industry. PRRSV has been recognized to modulate the host immune response through a number of mechanisms. In our previous study, we found that over-expression of ZAP, a zinc finger antiviral protein of host, could suppress PRRSV replication, but how PRRSV escape the restriction of ZAP under natural conditions was still unknown. In this study, We found PRRSV infection significantly down-regulate the endogenous ZAP protein expression in Marc-145 cells. And PRRSV nonstructural protein 4 (Nsp4), a 3C-like serine proteinase, was screened to be responsible for ZAP reduction. Nsp4 could cleave ZAP, depending on its protease activity. The anti-PRRSV activity of ZAP was antagonized by Nsp4 in Marc-145 cells. In addition, we identified a unique amino acid, serine 180 of Nsp4 was required for efficient degradation of ZAP, and the mutation at residue 180 could decrease the ability of recombinant PRRSV to degrade ZAP. Those findings reveal a manner of PRRSV Nsp4 antagonizing the antiviral activity of ZAP, and shed light on a new strategy evolved by PRRSV to escape the host defense.

Hydroquinone inhibits PRV infection in neurons in vitro and in vivo

Pseudorabies virus (PRV) is a prevalent and endemic swine pathogen that causes significant economic losses in the global swine industry. Due to the emergence of PRV mutant strains in recent years, vaccines can't completely prevent and control PRV infection. Therefore, research and development of new vaccines and drugs with inhibitory effects on PRV are of great significance in the prevention and treatment of PR. In this study, we firstly screened a library of 44 FDA-approved drugs and found that hydroquinone (HQ) displayed high anti-PRV activity by inhibiting PRV adsorption onto and internalization into cells. This study revealed that hydroquinone treatment stimulated genes associated with the PI3K-AKT signal pathway. HQ increased AKT mRNA production and activated AKT phosphorylation in N2a cells. This finding suggests that HQ significantly inhibits PRV replication by activating the phosphorylation of AKT. We also conducted in vivo experiments in mice. Hydroquinone significantly reduced the viral loads in mouse tissues and the mortality after PRV infection. The above results indicate that hydroquinone significantly inhibits the replication of PRV mutant strain ZJ01 in ICR mice and has an inhibitory effect on PRV. This study will contribute to the development of a novel prophylactic and therapeutic strategy against PRV infection.

Genetic analysis of a porcine reproductive and respiratory syndrome virus 1 strain in China with new patterns of amino acid deletions in nsp2, GP3 and GP4

Porcine reproductive and respiratory syndrome virus (PRRSV) 1 and PRRSV 2 have coexisted in China for a very long time. In this study, the complete genomic characterization of a PRRSV 1 strain named KZ2018 was conducted. The results showed that it shared 88.6% identity with Lelystad virus and 81.9-90.8% identities with other Chinese PRRSV 1 strains. Further study showed that its nsp2 protein had a unique discontinuous 6-amino acid (aa) deletion (aa357-360+aa411+aa449). Additionally, its GP3 and GP4 contained a long continuous 18-aa deletion in their overlapped region, which has never been described in other Chinese PRRSV 1 isolates. Amino acid analysis of cell epitopes revealed that GP3_245-256 and GP4_57-68 were the most variable epitopes among different Chinese PRRSV 1 isolates. The results might enrich our knowledge of PRRSV 1 strains in China.

Full Genomic Analysis of New Variants of Porcine Reproductive and Respiratory Syndrome Virus Revealed Multiple Recombination Events Between Different Lineages and Sublineages

Porcine reproductive and respiratory syndrome virus (PRRSV) has had a devastating impact on the pig industry in China, and monitoring its genetic diversity is important for epidemiological surveillance and understanding its evolution. Here, we determine the complete genome sequences of two PRRSV strains, GXYL1403 and GXNN1839. Comparative, phylogenetic, and recombination detection program analyses show that the two isolates are recombinant strains with large-fragment amino acid deletions in nsp2. GXYL1403 possesses a unique deletion region of 124 amino acids in nsp2, and GXNN1839 contains a deletion of 131 amino acids in nsp2 as compared with VR2332. Further analysis of the full-length sequence suggests that GXYL1403 is a natural recombinant between sublineages 8.1 (CH-1a like) and 8.3 (JXA1-like). The recombination site of GXYL1403 is located in nsp9–nsp12 (8961nt−11181nt). GXNN1839 is a natural recombinant between the lineage 5 (VR-2332-like) and lineage 1 (NADC30-like) strains. The recombination events occurred in nsp9 (7872nt-8162nt) and in ORF2 (12587nt−13282nt) in the genome of GXNN1839. These results provide new evidence that PRRSV strains circulating in the environment have undergone recombination among the different lineages or sublineages of field strains, and these add to our understanding of RNA combination events that occur in PRRSV.

Epidemiological and genetic characteristics of porcine reproduction and respiratory syndrome virus 2 in mainland China, 2017-2018

Porcine reproductive and respiratory syndrome virus 2 (PRRSV2) is a major threat to the global pig industry, particularly in China, the world's largest pig-rearing and pork-production country. Continuously monitoring the epidemiological and genetic characteristics of PRRSV epidemic strains is beneficial for prevention and control of infection. Previously, we reported the epidemiological and genetic characteristics of PRRSV2 in China from 2012 to 2016. Here, the epidemiological and genetic characteristics of PRRSV2 in China from 2017 to 2018 are reported. During these two years, we collected different types of porcine samples from 2428 pig farms in 27 provinces in China. Of the 7980 samples collected, 2080 (26.07%) were positive for PRRSV2 ORF5 by RT-PCR. The positive rate of PRRSV detection between different regions of China ranged from 8.12% to 29.33%, and from 7.96% to 55.50% between different months. Phylogenetic analysis based on the ORF5 gene revealed that the PRRSV2 strains currently circulating in China belong to five clades, and most of the PRRSVs detected are highly pathogenic PRRSVs (HP-PRRSVs; clade IV) and PRRSV NADC30-like strains (clade I). Sequence analysis revealed multiple amino acid mutation types, including amino acid changes and deletions in both the GP5 and Nsp2 proteins. The presence of these mutations may have an effect on the evolution of the virus by altering the viral titer and/or affecting the antibody response against the virus.

Genetic Diversity of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) From 1996 to 2017 in China

Porcine reproductive and respiratory syndrome (PRRS) is one of the most devastating diseases of the global swine industry. The causative agent porcine reproductive and respiratory syndrome virus (PRRSV) was first isolated in China in 1996 and has evolved quickly during the last two decades. To fully understand virus diversity, epidemic situation in the field, and make future predictions, a total of 365 PRRSV strains were used for evolution and genome analysis in which 353 strains were isolated from mainland China. The results showed that high diversity was found among PRRSV isolates. Total PRRSV isolates could be divided into eight subgroups. Among these subgroups strains, Original HP-PRRSV, NADC30-like, and Intermediate PRRSV were the major epidemic PRRSV strains circling in the field and would play a major role in PRRS epidemic in the future. Deletions, insertions, and recombinations have occurred frequently in the PRRSV genome. Deletions were the main driving force of viral evolution before 2006 and may also contribute further to the virus' evolution in a relatively closed or low strain diversity circumstance. The recombinant strains could be divided into three groups: the Inner group, Extensional group, and Propagating group. The evolutionary directions of the isolates in the Extensional and Propagating groups have changed, and the routes of recombination in the Propagating group were analyzed and sorted into three types. The increases in recombinant strains and high rates of recombination in recent years indicate that recombination has played a very important role in the virus' evolution. Isolates, which incorporate the advantages of their parental strains, will influence PRRSV evolution and make adverse effects on PRRS control in the future.

Pathogenicity and immunogenicity of a new strain of porcine epidemic diarrhea virus containing a novel deletion in the N gene

Since late 2010, highly virulent PEDV G2-genotype strains have emerged globally extracting heavy losses on the pork industries of numerous countries. We investigated the characteristics of a field strain of PEDV (PEDV strain SH) isolated from a piglet with severe diarrhea on a farm in Shanghai China. Whole genome sequencing and analysis revealed that the SH strain belonged to subtype G2b and has a unique 12-aa deletion (aa 399-410) including the antigenic epitope NEP-1C9 (aa 398-406) of the N protein. PEDV SH strain is highly pathogenic to challenged newborn piglets, resulting in 100 % morbidity and mortality. Pathological examination revealed significant villus atrophy in the jejuna of infected piglets. Mice inoculated with inactivated PEDV SH produced antibodies against the N protein, but no antibodies against the deletions. These results illustrated that deletion of the NEP-1C9 epitope had no effect on the immunogenicity or pathogenicity of PEDV, providing evidence of the necessity to monitor the genetic diversity of the virus. Our study also contributes to development of candidate for vaccines and diagnostics that could differentiate pigs seropositive due to vaccination by conventional strains from wild virus infection.

S100A9 regulates porcine reproductive and respiratory syndrome virus replication by interacting with the viral nucleocapsid protein

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused huge economic losses to the pig industry worldwide over the last 30 years, yet the associated viral-host interactions remain poorly understood. S100A9 is a damage-associated molecular pattern of the S100 protein family. Here, we found that PRRSV infection stimulated S100A9 expression in porcine alveolar macrophages (PAMs) and Marc-145 cells. S100A9 inhibited PRRSV replication via cellular Ca²⁺ dependent manner. The viral nucleocapsid (N) protein co-localized with S100A9 in the cytoplasm, and directly interacted at amino acid 78 of S100A9 and amino acids 36-37 of N protein. Moreover, we also found that the mutant S100A9 (E78Q) protein exhibited decreased antiviral activity against PRRSV compared with the parent S100A9. Recombinant PRRSV rBB (36/37) with two mutations in amino acid 36-37 in the N protein exhibited greater replication than the parent PRRSV BB0907 in S100A9-overexpressed PAM and Marc-145 cells. Thus, S100A9 may restrict PRRSV proliferation by interacting with the viral N protein.