Epidemiological and genetic characteristics of porcine reproductive and respiratory syndrome virus circulating in central and South China in 2016

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.

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

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

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.

Infection of PRRSV inhibits CSFV C-strain replication by inducing macrophages polarization to M1

It is a common sense that porcine reproductive and respiratory syndrome virus (PRRSV) infection could cause immune failure of classical swine fever (CSF) vaccine, and porcine alveolar macrophages (PAMs) are the target cells of both. To elucidate the role of macrophage polarization in PRRSV infection induced CSF vaccine failure, an immortal porcine alveolar macrophage line PAM39 cell line was used to investigate the effect of PRRSV or/and CSFV C-strain (CSFV-C) infection on macrophage polarization in vitro. Interestingly, PRRSV single infection or PRRSV co-infection with CSFV-C promoted PAM39 cells to M1, while CSFV-C single infection induced PAM39 cells to M2. After the construction of M1 and M2 PAM39 cells polarization models, M1 polarized PAM39 cells were found to inhibit the replication of CSFV-C, and Chinese medicine such as matrine, ginsenosides and astragalus polysaccharides could alleviate the polarization of PAM39 cells and the replication of CSFV-C. Furthermore, interferon (IFN)-γ and lipopolysaccharide (LPS) co-stimulation induced NF-κB activation while matrine treatment blocked M1 polarization-induced NF-κB pathway activation. These findings provided a theoretical basis for designing a new strategy to improve the immune effect of CSFV-C based on porcine alveolar macrophage polarization subtypes.

Development of a Real-Time TaqMan RT-PCR Assay for the Detection of NADC34-like Porcine Reproductive and Respiratory Syndrome Virus

NADC34-like porcine reproductive and respiratory syndrome virus first appeared in 2017 in a herd of pigs in Liaoning Province, China. The virus was subsequently found in other provinces. Given the potential for this virus to cause an epidemic, rapid, sensitive, and specific detection of NADC34-like PRRSV is required. The virus' ORF5 gene was artificially synthesized based on a Chinese reference strain, and specific primers/probes for the ORF5 gene were designed. Then, the amplified target fragment was cloned into the pMD19-T vector, and a series of diluted recombinant plasmids were used to generate a standard curve. An optimized real-time TaqMan RT-PCR method was established. The method was highly specific for NADC34-like PRRSV, without cross-reactions with other non-targeted pig viruses. The detection limit of this assay was 10¹ copies/μL. The method had an efficiency of 98.8%, a squared regression value (R²) of 0.999, and showed a linear range of 10³-10⁸ copies/μL of DNA per reaction. This method was shown to be analytically specific and sensitive with a low intra- and inter-assay coefficient of variation (<1.40%). A total of 321 clinical samples were tested using the established method, and four were shown to be positive (1.24%). This study confirmed the existence of NADC34-like PRRSV and HP-PRRSV co-infection in Sichuan and provided a promising alternative tool for the rapid detection of NADC34-like PRRSV.

Development of a Multiplex Crystal Digital RT-PCR for Differential Detection of Classical, Highly Pathogenic, and NADC30-like Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) type 1 (European genotype) and PRRSV type 2 (North American genotype) are prevalent all over the world. Nowadays, the North American genotype PRRSV (NA-PRRSV) has been widely circulating in China and has caused huge economic losses to the pig industry. In recent years, classical PRRSV (C-PRRSV), highly pathogenic PRRSV (HP-PRRSV), and NADC30-like PRRSV (NL-PRRSV) have been the most common circulating strains in China. In order to accurately differentiate the circulating strains of NA-PRRSV, three pairs of specific primers and corresponding probes were designed for the Nsp2 region of C-PRRSV, HP-PRRSV, and NL-PRRSV. After optimizing the annealing temperature, primer concentration, and probe concentration, a multiplex real-time quantitative RT-PCR (qRT-PCR) and a multiplex Crystal digital RT-PCR (cdRT-PCR) for the differential detection of C-PRRSV, HP-PRRSV, and NL-PRRSV were developed. The results showed that the two assays illustrated high sensitivity, with a limit of detection (LOD) of 3.20 × 10⁰ copies/μL for the multiplex qRT-PCR and 3.20 × 10^-1 copies/μL for the multiplex cdRT-PCR. Both assays specifically detected the targeted viruses, without cross-reaction with other swine viruses, and indicated excellent repeatability, with coefficients of variation (CVs) of less than 1.26% for the multiplex qRT-PCR and 2.68% for the multiplex cdRT-PCR. Then, a total of 320 clinical samples were used to evaluate the application of these assays, and the positive rates of C-PRRSV, HP-PRRSV, and NL-PRRSV by the multiplex qRT-PCR were 1.88%, 21.56%, and 9.69%, respectively, while the positive rates by the multiplex cdRT-PCR were 2.19%, 25.31%, and 11.56%, respectively. The high sensitivity, strong specificity, excellent repeatability, and reliability of these assays indicate that they could provide useful tools for the simultaneous and differential detection of the circulating strains of C-PRRSV, HP-PRRSV, and NL-PRRSV in the field.

Epidemiology and Genetic Characteristics of Porcine Reproductive and Respiratory Syndrome Virus in the Hunan and Hebei Provinces of China

Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant threat to the pig industry in China. However, the epidemiological characteristics of PRRSV after the outbreak of African swine fever in China were not thoroughly investigated. In the present study, the serological and epidemiological investigations of PRRSV in pigs from the Hunan and Hebei provinces of China were assessed. The results showed that 73.12% (95% CI 71.74-74.49) of pigs were positive for PRRSV-special antibody by enzyme-linked immunosorbent assay. Out of 5799 samples, 482 (8.31%, 95% CI 7.60-9.02) samples were positive for PRRSV nucleic acids. The positive rates of PRRSV in healthy pigs from farms and slaughterhouses were 2.27% (47/2072) and 7.70% (217/2818), which were lower than that in diseased pigs (23.98%, 218/909). Furthermore, the full-length OFR5 gene sequences of 43 PRRSV strains were sequenced and analysed. Phylogenetic analysis revealed that 43 isolates were classified into three lineages, namely lineage 1 (n = 24), lineage 8 (n = 15), and lineage 3 (n = 4). Lineage 1 could be further divided into sublineage 1.5 (n = 2) and sublineage 1.8 (n = 22), and lineage 8 was classified into sublineage 8.1 (n = 3) and sublineage 8.7 (n = 12). Collectively, our findings revealed the severe prevalence of PRRSV in the Hunan and Hebei provinces, where sublineage 1.8 and sublineage 8.7 predominated. The present study provides the update information of the epidemiological and genetic characteristics of PRRSV in the investigated regions, which will be beneficial for PRRS control.

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

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

Genetic characterization of porcine reproductive and respiratory syndrome virus from Eastern China during 2017-2022

Porcine reproductive and respiratory syndrome (PRRS) is an immunosuppressive disease caused by PRSS virus (PRRSV). PRRSV mainly causes reproductive disorders in pregnant sows and respiratory diseases in piglets. Recently, it has emerged as one of the most important diseases of the pig industry across the globe. In this study, we have collected 231 samples from differently sized pig farms in Eastern China from 2017 to 2022 to investigate the epidemic characteristics of the disease. All samples were screened by RT-PCR and analyzed further using Nsp2 and ORF5 genes. The result showed that the positive rate of PRRSV was 24% (54/231). Phylogenetic analysis (13 positive samples) revealed that all isolates belonged to genotype 2, and they were mainly distributed in four lineages (i.e., lineage 1, 3, 5, and 8). Nsp2 is the most variable protein among all PRRSV NSPs, several isolates from this study had amino acid deletions within Nsp2 compared to that of strain VR-2332. The major structural protein glycoprotein (GP5) protein is encoded by ORF5. Epitope analysis of the 13 isolated strains and additional reference strains revealed that all 13 strains had some mutations on the decoy epitope, the primary neutralizing epitope, T cell epitopes, and B cell epitopes. This study showed that the prevalent PRRSV strain in Eastern China was still HP-PRRSV, while the proportion of NADC30-like and NADC34-like strains have increased. This study further enriches the epidemiological data of PRRS in Eastern China and provides a theoretical basis for vaccine development and prevention and control of the disease across the region.

Investigation and analysis of etiology associated with porcine respiratory disease complex in China from 2017 to 2021

Porcine respiratory diseases complex (PRDC) is a highly serious threat to the pig industry. In the present study, we investigated and analyzed the etiology associated with PRDC and explored the role of viruses in respiratory bacterial infections. From 2017 to 2021, clinical samples were collected from 1,307 pigs with typical respiratory symptoms in 269 farms in China and screened for pathogens related to PRDC by PCR and bacterial isolation. The results indicated that PRRSV (41.16%, 95%CI: 38.49~43.83%), PCV2 (21.58%,95%CI: 19.35~23.81%), S. suis (63.50%, 95%CI: 60.89~66.11%), and G. parasuis (28.54%, 95%CI: 26.09~30.99%) were the most commonly detected pathogens in pigs with PRDC in China. The dominant epidemic serotypes (serogroups) of S. suis, G. parasuis, and P. multocida were serotype 2, serotype 1, and capsular serogroups D, respectively. Pigs of different ages exhibited different susceptibilities to these pathogens, e.g., PRRSV, PCV2, and G. parasuis had the highest detection rates in nursery pigs, whereas fattening pigs had the highest detection rates of P. multocida and A. pleuropneumoniae. Among the 1,307 pigs, the detection rates of S. suis, G. parasuis, P. multocida, and B. bronchiseptica were higher in virus-positive pigs, especially G. parasuis and P. multocida were significantly (p < 0.01) higher than in virus-negative pigs. In addition, a strong positive correlation was found between coinfection by PRRSV and G. parasuis (OR = 2.33, 95%CI: 1.12~2.14), PRRSV and P. multocida (OR = 1.55, 95%CI: 1.12~2.14), PCV2 and P. multocida (OR = 2.27, 95%CI: 1.33~3.87), PRRSV-PCV2 and S. suis (OR = 1.83, 95%CI: 1.29~2.60), PRRSV-PCV2 and G. parasuis (OR = 3.39, 95%CI: 2.42~4.74), and PRRSV-PCV2 and P. multocida (OR = 2.09, 95%CI: 1.46~3.00). In summary, PRRSV, PCV2, S. suis, and G. parasuis were the major pathogens in pigs with PRDC, and coinfections of two or more PRDC-related pathogens with strong positive correlations were common in China, such as PRRSV and G. parasuis, PRRSV and P. multocida, PCV2 and P. multocida, and also PRRSV-PCV2 and G. parasuis and PRRSV-PCV2 and P. multocida.

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.

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.

On-site differential diagnostic detection of HP-PRRSV and C-PRRSV using EuNPs-mAb fluorescent probe-based immunoassay

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused worldwide economic losses in the swine industry. Pigs infected with highly pathogenic (HP)-PRRSV display more severe symptoms than those infected with classical (C)-PRRSV. A rapid, sensitive, and reliable detection method to distinguish between HP-PRRSV and C-PRRSV is needed. In this study, we prepared a monoclonal antibody from a hybridoma that can distinguish HP-PRRSV(including TP, QJ, LQ, JN-HS, and TY strain) from C-PRRSV (CH-1A strain) using cell surface-fluorescence immunosorbent assays (CSFIA). Based on this monoclonal antibody (4D5), we developed a europium microsphere-based lateral flow immunochromatographic strip (EuNPs-LFICS) for the differential diagnostic detection of HP-PRRSV and C-PRRSV. Under optimized conditions, the method was rapid (15 min), sensitive (LOD: 2.57 ng mL^-1, 606 TCID50/0.1 mL), selective for HP-PRRSV detection, and quantitative (DLR: 3.56-228 ng mL^-1). In clinical samples, the EuNPs-LFICS assay was largely consistent with PCR results, indicating its practical clinical application.

Prevalence of porcine respiratory pathogens in slaughterhouses in Shanxi Province, China

Background

Porcine respiratory diseases remain the biggest challenge in pig‐based food production and are a public health concern. Despite control measures, persistent outbreaks have been reported worldwide.

Objective

To establish an early detection mechanism for pig farm disease outbreaks based on slaughterhouse risk and environmental assessment.

Methods

We investigated the prevalence and risk factors of porcine respiratory disease‐causing pathogens including Mycoplasma hyopneumoniae (MHP), porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV) and Haemophilus parasuis (HPS). Polymerase chain reaction (PCR) was used to analyse the lungs of 491 pigs from 19 slaughterhouses across 11 cities in Shanxi Province, China.

Results

PCR detected MHP, PCV2, PPRSV and HPS in 76.99%, 67.00%, 11.82% and 19.55% of the samples, respectively; 10.12% were negative for all four pathogens. Co‐positivity rates for two and three pathogens were identified. The results confirmed significant correlations between PCV2 and MHP (p = .001, p < .05), HPS and PCV2 (p = .01, p < .05) and MHP and PRRSV (p = .01, p < .05). No significant correlation was observed between HPS and MHP (p = .067, p > .05). Positive MHP and PCV2 rates were low in areas with high vegetation coverage. The overall pathogen positivity rate was higher in both lower and higher temperature environments.

Conclusions

Interactions among pathogens may increase disease severity. Furthermore, environmental assessment and pathogen surveillance within pig slaughterhouses can be an effective approach for early detection and mitigation of new disease threats before broad dissemination occurs among a herd.

Molecular Characterization of the Nsp2 and ORF5 (ORF5a) Genes of PRRSV Strains in Nine Provinces of China During 2016-2018

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly contagious disease and brings huge economic losses to commercial pork production worldwide. PRRSV causes severe reproductive failure in sows and respiratory distress in piglets. To trace the evolution of PRRSV in pigs with respiratory diseases in some regions of China, 112 samples were collected from nine provinces in China during 2016–2018. All samples were detected by RT-PCR and analyzed by the Nsp2/ORF5 (ORF5a)-genes-phylogeny. Sequence analysis and recombination analysis were conducted on the Nsp2/ORF5 (ORF5a) genes of the identified strain in the study. The RT-PCR result shown that the positive rate of PRRSV was 50.89% (57/112). Phylogenetic analysis showed that the identified PRRSV strains were all NA genotype and belonged to lineage 1, 3, and 8. The Nsp2 gene of identified PRRSV strains exhibited nucleotide homologies of 53.0 ~ 99.8%, and amino acid homologies of 46.8 ~ 99.7%. The ORF5 gene of identified PRRSV strains exhibited nucleotide homologies of 82.4 ~ 100%, and amino acid homologies of 79.6 ~ 100%. Sequence analysis revealed that a discontinuous 30-amino-acid deletion (positions 481 and 533–561) and a 131-amino-acid discontinuity deletion (positions 323–433, 481, and 533–551) in Nsp2 of PPRSV isolates; all identified strains in this study may be wild strains, and most identified strains may be highly virulent strains. Sequence analysis of ORF5 and ORF5a revealed that the mutation sites of GP5 were mainly concentrated in the signal peptide and epitopes region, while the mutation sites of ORF5a were mainly concentrated in the transmembrane and the intramembrane region. The recombination analysis indicated that there may be multiple recombination regions in identified strains, and the recombination pattern was more complex. This study showed that the prevalent PRRSV strain in some regions of China was still HP-PRRSV, while NADC30 strain also occupied a certain proportion; different types of PRRSV strains showed different patterns and variation in China. This study suggested that the monitoring of PRRSV prevalence and genetic variation should be further strengthened.

Research progress in the development of porcine reproductive and respiratory syndrome virus as a viral vector for foreign gene expression and delivery

INTRODUCTION

Porcine reproductive and respiratory syndrome (PRRS) is an infectious disease of swine characterized by respiratory disorders in growing and finishing pigs and reproductive failure in pregnant sows. PRRSV has been recognized as one of the most economically significant pathogens affecting the global pig industry.

AREAS COVERED

Currently, commercially available vaccines, including traditional killed virus (KV) vaccines and modified live virus (MLV) vaccines, are the cardinal approaches to prevent and control porcine reproductive and respiratory syndrome virus (PRRSV) infection. However, the protective efficacy of these vaccines is not satisfactory, resulting in the continuous evolution and recurrent appearance of the virus as well as the emergence of new variants. A safe and effective vaccine against PRRSV is in dire need. Here, we review the research progress in recent years in the development and use of PRRSV as a viral vector to express foreign genes, and their potential application in gene delivery and vaccine development.

EXPERT OPINION

The potential of using PRRSV-based vectors to express multiple antigens would be particularly instrumental for the development of a new generation of multivalent vaccines against PRRSV and other porcine viruses.

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.

Construction and immunological evaluation of recombinant Newcastle disease virus vaccines expressing highly pathogenic porcine reproductive and respiratory syndrome virus GP3/GP5 proteins in pigs

Highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) poses a significant threat to the pig industry, for which vaccination is considered to be an effective means of prevention and control. Here, we developed two recombinant Newcastle disease virus (NDV) LaSota-vectored PRRS candidate vaccines, rLaSota-GP5 and rLaSota-GP3-GP5, using reverse genetic techniques. The two recombinant viruses exhibited a high degree of genetic stability after 10 successive generations in chicken embryos. There was no significant difference in pathogenicity compared with the rLaSota parent strain in poultry, mice and pigs. The recombinant viruses could not be detected in the feeding environment of immunized pigs, but could be detected in the organs and tissues of pigs for no more than 10 days after immunization. Importantly, in contrast to rLaSota-GP5, rLaSota-GP3-GP5 elicited both significant humoral and cellular immune responses in pigs. In particular, the neutralizing antibody titer in the rLaSota-GP3-GP5 group was 1.51 times significantly higher than that of the commercial vaccine group at 42 days post-immunization. At the same time, there was significant difference in the level of IFN-γ between the rLaSota-GP3-GP5 group and the commercial vaccine group. Furthermore, the viral load in the organs and tissues of rLaSota-GP3-GP5-immunized pigs was substantially lower than that of unimmunized pigs after being challenged with HP-PRRS virus GD strain. These results suggest that rLaSota-GP3-GP5 is a safe and promising candidate vaccine, and there is potential for further development of a recombinant virus vaccine for PRRS using NDV.