Comparison of the structural protein coding sequences of the VR-2332 and Lelystad virus strains of the PRRS virus

Molecular characterization of porcine reproductive and respiratory syndrome virus identified in 2021 from Nepal

Porcine reproductive and respiratory syndrome (PRRS), an important viral disease of swine caused by PRRS virus (PRRSV) was first confirmed in Nepal in 2013. Since then, the virus has spread throughout the country and has now become endemic affecting the pig production nationally. However, molecular characterization of circulating strains has not been done in Nepal yet. In the present study, serum samples were collected from outbreak areas of different districts of Nepal and samples positive for PRRSV by ELISA were sent to Animal and Plant Health Agency (APHA), United Kingdom for sequence analysis. Out of 35 samples that were sent to APHA, only one sample was found positive by PCR and subjected to sequence analysis based on ORF5, ORF7 and Nsp2. The results from the phylogenetic analysis demonstrated that the PRRSV strain belongs to PRRSV-2 and lineage 8 strain. The sequences from the Nepalese PRRSV strain revealed a high degree of similarity with the strains isolated from India, China and Vietnam, with the closest genetic relatedness to the Indian isolates from 2020 and 2018. This is the first study on molecular characterization of PRRS virus circulating in Nepal. Further studies on strains circulating in Nepal are very essential to understand the virus diversity, its spread and evolution.

The scene of lung pathology during PRRSV-1 infection

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important infectious diseases for the pig industry worldwide. The disease was firstly reported in 1987 and became endemic in many countries. Since then, outbreaks caused by strains of high virulence have been reported several times in Asia, America and Europe. Interstitial pneumonia, microscopically characterised by thickened alveolar septa, is the hallmark lesion of PRRS. However, suppurative bronchopneumonia and proliferative and necrotising pneumonia are also observed, particularly when a virulent strain is involved. This raises the question of whether the infection by certain strains results in an overstimulation of the proinflammatory response and whether there is some degree of correlation between the strain involved and a particular pattern of lung injury. Thus, it is of interest to know how the inflammatory response is modulated in these cases due to the interplay between virus and host factors. This review provides an overview of the macroscopic, microscopic, and molecular pathology of PRRSV-1 strains in the lung, emphasising the differences between strains of different virulence.

Research progress on the E protein of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is an economically important disease impacting the global pig industry, and it is characterized by reproductive disorder in sows and respiratory disorder in pigs of all ages. The PRRSV E protein is a nonglycosylated structural protein encoded by the ORF2b gene. The E protein is not necessary for the assembly of virus particles, but deletion of the E protein leads to transmissible virus particles not being produced. To better understand the structure and function of the E protein, we reviewed its genetic and evolutionary analysis, characteristics, subcellular localization and topology, ion channel activity, cellular immune response, additional biological functions, interactions with host proteins, interactions with PRRSV proteins, roles in infection, pathogenicity, and drugs. Therefore, this review can provide a theoretical basis for gaining an in-depth understanding of the E protein of PRRSV-2.

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.

Comparative analysis of newly identified rodent arteriviruses and porcine reproductive and respiratory syndrome virus to characterize their evolutionary relationships

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused huge economic losses for the global pig industry, but its origins and evolution remain a mystery. In 2018, the genome sequences of seven arteriviruses isolated from rodents were determined, and here we publish new analysis showing that they may be ancestors of PRRSV. The sequence similarity of these viruses to PRRSV was ~60%, with shared genome organization and other characteristics, such as slippery sequences and C-rich motifs in nsp2, and a transactivated protein sequence in nsp1β. Codon usage basis analysis showed that PRRSV was closer to these rodent arteriviruses than lactate dehydrogenase-elevating virus (LDV) and they were both under pressure of natural selection. Evolutionary analysis revealed that four of the rodent arteriviruses shared the same genus with PRRSV, and were more closely related to PRRSV-2 than PRRSV-1. In addition to this, they all appeared earlier than PRRSV according to evolutionary modeling, and we speculate that they represent an intermediate step in the origin of PRRSV by arterivirus transmission from rodents to swine. Our in-depth analysis furthers our understanding of arteriviruses, and will serve as the basis for subsequent exploration of the evolution of PRRSV and other arteriviruses.

Research Progress on the detection methods of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) causes clinical syndromes typified as reproductive disorders in sows and respiratory diseases in piglets. PRRSV remains one of the most prevalent pathogens affecting the pig industry, because of its complex infection profile and highly heterogeneous genetic and recombination characteristics. Therefore, a rapid and effective PRRSV detection method is important for the prevention and control of PRRS. With extensive in-depth research on PRRSV detection methods, many detection methods have been improved and promoted. Laboratory methods include techniques based on virus isolation (VI), enzyme-linked immunosorbent assays (ELISA), indirect immunofluorescence assays (IFA), immunoperoxidase monolayer assays (IPMA), polymerase chain reaction (PCR), quantitative real-time PCR (qPCR), digital PCR (dPCR), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), clustered regularly interspaced short palindromic repeats (CRISPR), metagenomic next-generation sequencing (mNGS), and other methods. This study reviews the latest research on improving the main PRRSV detection methods and discusses their advantages and disadvantages.

Implementing a user-friendly format to analyze PRRSV next-generation sequencing results and associating breeding herd production performance with number of PRRSV strains and recombination events

The open reading frames (ORF)5 represents approximately 4% of the porcine reproductive and respiratory syndrome virus (PRRSV)-2 genome (whole-PRRSV) and is often determined by the Sanger technique, which rarely detects >1 PRRSV strain if present in the sample. Next-generation sequencing (NGS) may provide a more appropriate method of detecting multiple PRRSV strains in one sample. This work assessed the effect of PRRSV genetic variability and recombination events, using NGS, on the time-to-low prevalence (TTLP) and total losses in breeding herds (n 20) that detected a PRRSV outbreak and adopted measures to eliminate PRRSV. Serum, lung or live virus inoculation material collected within 3-weeks of outbreak, and subsequently, processing fluids (PFs) were tested for PRRSV by RT-qPCR and NGS. Recovered whole-PRRSV or partial sequences were used to characterize within and between herd PRRSV genetic variability. Whole-PRRSV was recovered in five out of six (83.3%) lung, 16 out of 22 (72.73%) serum and in five out of 95 (5.26%) PF. Whole-PRRSV recovered from serum or lung were used as farm referent strains in 16 out of 20 (80%) farms. In four farms, only partial genome sequences were recovered and used as farm referent strains. At least two wild-type PRRSV strains (wt-PRRSV) were circulating simultaneously in 18 out of 20 (90%) and at least one vaccine-like strain co-circulating in eight out of 20 (40%) farms. PRRSV recombination events were detected in 12 farms (59%), been 10 out of 12 between wt-PRRSV and two out of 12 between wt-PRRSV and vaccine-like strains. Farms having ≥3 strains had a 12-week increase TTLP versus herds ≤2 strains detected. Farms with ≤2 strains (n 10) had 1837 and farms with no recombination events detected (n 8) had 1827 fewer piglet losses per 1000 sows versus farms with ≥3 PRRSV strains (n 8) or detected recombination (n 10), respectively. NGS outcomes and novel visualization methods provided more thorough insight into PRRSV dynamics, genetic variability, detection of multiple strains co-circulating in breeding herds and helped establish practical guidelines for using PRRSV NGS outputs.

Identification of MHC-I-Presented Porcine Respiratory and Reproductive Syndrome Virus (PRRSV) Peptides Reveals Immunogenic Epitopes within Several Non-Structural Proteins Recognized by CD8+ T Cells

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most relevant porcine pathogens worldwide. Active control of the disease relies on modified live virus vaccines (MLVs), as most inactivated vaccines provide very limited protection. Neutralizing antibodies occur late in infection; therefore, CD8⁺ T cells are considered important correlates of protection and are a frequent focus of investigation. Our aim was to identify viral peptides naturally bound by the class I major histocompatibility complex (MHC-I) and to confirm their ability to stimulate CD8⁺ T cells. For this purpose, we immunoprecipitated MHC-I/peptide complexes of PRRSV (strain AUT15-33) -infected cells (SLA-I Lr-Hp 35.0/24 mod) to isolate the viral epitopes and analyzed them with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Furthermore, we employed these identified peptides to stimulate peripheral blood mononuclear cells (PBMCs) of previously PRRSV-infected pigs and measured the PRRSV-specific CD8⁺ T-cell response with an intracellular cytokine staining (ICS). Our data revealed that PRRSV non-structural proteins (NSPs), encoded in open reading frame 1a and 1b (ORF1), present the major source of MHC-I-presented peptides. Additionally, we show that our identified epitopes are able to trigger IFNγ responses in vitro. These findings are a basis for understanding the proteasomal degradation of PRRSV proteins, the cellular ability to display them via MHC-I, and their potential to restimulate CD8⁺ T cells.

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.

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.

Heterologous Challenge with PRRSV-1 MLV in Pregnant Vaccinated Gilts: Potential Risk on Health and Immunity of Piglets

Simple Summary

Modified live virus (MLV) vaccines are considered as the key component to control the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). The majority of pig farms apply the ‘mass’ vaccination strategy in breeding female animals. However, this PRRS MLV vaccination protocol involves the risk of inoculation of sows in the last stage of gestation, resulting in possible infection of the fetus as the virus can efficiently cross the placenta during the last period of pregnancy. Thus, we evaluated the ability of the vaccine virus to act as a pathogenic strain, to be transmitted to fetuses and to affect the health status of neonatal piglets. The results indicated that the study gilts transmitted the vaccine virus to their offspring, as well as that the PRRSV-infected piglets showed a poor clinical performance. Consequently, the pig farms that apply PRRS MLV vaccination in a routine blanket vaccination strategy must avoid inoculating pregnant gilts the last week before their parturition.

Abstract

The objective of the present study was to evaluate the potential risks of the four commercial PRRS-1 MLV vaccines in pregnant vaccinated gilts at the last stage of gestation under field conditions. The study was conducted at four pig farms, including 25 gilts from each farm (25 × 4 = 100 gilts), which were equally allocated to five different study groups. A PRRS-1 MLV vaccination was applied on the 100th day of their pregnancy with the different commercial vaccines that are available in the Greek market. The results indicated virus congenital infection and viremia in piglets (20/200 = 10% PRRSV infected piglets), and detection of PRRSV-specific antibodies (181/200 = 90.5% piglets found with PRRSV antibodies). The subsequent phylogenetic analyses revealed high percentages of similarity between the PRRSV-1 strain detected in infected litters and the PRRSV-1 vaccine strain to which the study gilts had been previously exposed to. Health status analyses of trial piglets resulted in differences between litters from vaccinated sows and litters from non-vaccinated sows at 110th day of gestation as regards the number of weak-born piglets, mummies, and piglets with splay-leg and/or respiratory symptoms. The current study’s results indicate several potential dangers of the PRRS MLV vaccination in late gestation.

A Molecular and Epidemiological Description of a Severe Porcine Reproductive and Respiratory Syndrome Outbreak in a Commercial Swine Production System in Russia

Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating disease of swine in many parts of the world. Porcine reproductive and respiratory syndrome virus (PRRSV) type 1 is endemic in Europe, and prevalence of the subtypes differ spatially. In this study, we investigated a severe PRRS outbreak reported in 30 farms located in eastern Russia that belong to a large swine production company in the region that was also experiencing a pseudorabies outbreak in the system. Data included 28 ORF5 sequences from samples across 18 of the 25 infected sites, reverse transcriptase real-time polymerase chain reaction (RT-qPCR) results from diagnostic testing, reports of clinical signs, and animal movement records. We observed that the outbreak was due to two distinct variants of wildtype PRRSV type 1 subtype 1 with an average genetic distance of 15%. Results suggest that the wildtype PRRSV variants were introduced into the region around 2019, before affecting this production system (i.e., sow farms, nurseries, and finisher farms). Clinical signs did not differ between the variants, but they did differ by stage of pig production. Biosecurity lapses, including movement of animals from infected farms contributed to disease spread.

Recombination between NADC34-like and QYYZ-like strain of Porcine Reproductive and Respiratory Syndrome virus with high pathogenicity for piglets in China

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that causes huge economic losses to the swine industry worldwide. Here, a novel variant of PRRSV strain named TJnh2021 was isolated from nursery piglets with morbidity rate (75%) and mortality rate (40%) in Tianjin Province of China in 2021. Phylogenetic and molecular evolutionary analyses revealed that TJnh2021 was highly similar to NADC34-like (lineage1.5, isolated in North America in 2014) in the ORF1ab-ORF2 and ORF6-ORF7 coding regions, as well as to QYYZ-like (lineage3, isolated in China in 2010) in the ORF3-ORF5, suggestive of a natural recombination event. Recombination analyses revealed that recombination events occurred in two inter-lineage recombination events between lineages 1.5 and 3, and two breakpoints in ORF2 (nt12196) and ORF5(nt13628) (with reference to the VR-2332 strain). Animal experiments demonstrated that TJnh2021 caused mortality rates of 40% and exhibited higher pathogenicity in piglets compared to other lineage 1.5 strains reported in China. Taken altogether, NADC34-like PRRSV has undergone genetic exchange with Chinese local PRRSV strains and recombination might be responsible for the variations in pathogenicity and highlight the importance of surveillance of this lineage in China. This article is protected by copyright. All rights reserved.

A strain of highly pathogenic porcine reproductive and respiratory syndrome virus: genomic characterization, pathogenicity, and construction of an infectious full-length cDNA clone

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious infectious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV), which inflicts major economic losses on the global pig farming industry. Based on its similarity to highly pathogenic strains, the GDzj strain isolated in this study was predicted to be highly pathogenic. We therefore analyzed the pathogenicity of this strain experimentally in piglets. All piglets challenged with this virus experienced fever or high fever, loss of appetite, decreased food intake, daily weight loss, shortness of breath, and listlessness, and the necropsy results showed that they had experienced severe interstitial pneumonia. We then used the BAC system to construct a full-length cDNA infectious clone of GDzj, and the rescued virus displayed in vitro proliferation characteristics similar to those of the parental PRRSV strain. In summary, we successfully isolated a highly pathogenic PRRSV strain and constructed a full-length infectious cDNA clone from it, thereby providing an effective reverse genetics platform for further study of viral pathogenesis.

Investigating the relationship of porcine reproductive and respiratory syndrome virus RNA detection between adult/sow farm and wean-to-market age categories

Porcine reproductive and respiratory syndrome (PRRS) is a disease caused by the PRRS virus (PRRSV) that has spread globally in the last 30 years and causes huge economic losses every year. This research aims to 1) investigate the relationship between the PRRSV detection in two age categories (wean-to-market and adult/sow farm), and 2) examine the extent to which the wean-to-market PRRSV positive rate forecasts the adult/sow farm PRRSV positive rate. The data we used are the PRRSV RNA detection results between 2007 and 2019 integrated by the US Swine Disease Reporting System project that represent 95% of all porcine submissions tested in the US National Animal Health Network. We first use statistical tools to investigate to what extent the increase in PRRSV positive submissions in the wean-to-market is related to the PRRSV increase in adult/sow farms. The statistical analysis confirms that an increase in the PRRSV positive rate of wean-to-market precedes the increase in the adult/sow farms to a large extent. Then we create the dynamic exponentially weighted moving average control charts to identify out-of-control points (i.e., signals) in the PRRSV rates for both wean-to-market and adult/sow farms. This control-chart-based analysis finds that 78% of PRRSV signals in the wean-to-market are followed by a PRRSV rate signal in the adult/sow farms within eight weeks. We expect that our findings will help the producers and veterinarians to justify and reinforce the implementation of bio-security and bio-contaminant practices to curb disease spread across farms.

The jigsaw of PRRSV virulence

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of the, probably, most economically important disease for the pig industry worldwide. This disease, characterised by producing reproductive failure in sows and respiratory problems in growing pigs, appeared in the late 1980s in the United States and Canada. Since its appearance, strains capable of producing higher mortality rates as well as greater severity in clinical signs and lesions than classical strains have been identified. However, since the first reports of these "virulent" PRRSV outbreaks, no homogeneity and consensus in their description have been established. Moreover, to the authors' knowledge, there is no published information related to the criteria that a PRRSV strain should fulfil to be considered as a "virulent" strain. In this review, we revise the terminology used and gather the information related to the main characteristics and differences in clinical signs, lesions, viral replication and tropism as well as immunological parameters between virulent and classical PRRSV strains and propose a first approximation to the criteria to define a virulent PRRSV strain.

PRRSV2 genetic diversity defined by RFLP patterns in the United States from 2007 to 2019

The genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) increases over time. In 1998, restriction-fragment length polymorphism (RFLP) pattern analysis was introduced to differentiate PRRSV wild-type strains from VR2332, a reference strain from which a commercial vaccine (Ingelvac PRRS MLV) was derived. We have characterized here the PRRSV genetic diversity within selected RFLP families over time and U.S. geographic space, using available ISU-VDL data from 2007 to 2019. The 40,454 ORF5 sequences recovered corresponded to 228 distinct RFLPs. Four RFLPs [2-5-2 (21.2%), 1-7-4 (15.6%), 1-4-4 (11.8%), and 1-8-4 (9.9%)] represented 58.5% of all ORF5 sequences and were used for cluster analysis. Over time, there was increased detection of RFLPs 2-5-2, 1-7-4, 1-3-4, 1-3-2, and 1-12-4; decreased detection of 1-4-2, 1-18-4, 1-18-2, and 1-2-2; and different detection trends for 1-8-4, 1-4-4, 1-26-1, 1-22-2, and 1-2-4. An over-time cluster analysis revealed a single cluster for RFLP 2-5-2, supporting that sequences within RFLP 2-5-2 are still relatively conserved. For 1-7-4, 1-4-4, and 1-8-4, there were multiple clusters. State-wise cluster analysis demonstrated 4 main clusters for RFLP 1-7-4 and 1-8-4, and 6 for RFLP 1-4-4. For the other RFLPs, there was a significant genetic difference within them, particularly between states. RFLP typing is limited in its ability to discriminate among different strains of PRRSV. Understanding the magnitude of genetic divergence within RFLPs helps develop PRRSV regional control programs, placement, herd immunization strategies, and design of appropriate animal movements across borders to minimize the risk of PRRSV transmission.

Immunity against a Japanese local strain of porcine reproductive and respiratory syndrome virus decreases viremia and symptoms of a highly pathogenic strain

Background

The type 2 highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has spread throughout countries of southeast Asia, where it has caused severe economic losses. Even countries presently free of PRRSV are at high risk for infection and spread of this virus. Some of these countries, including Japan, have broad epidemics of the local type 2 PRRSV, creating chronic pathogenicity in the domestic pig population. The present study aimed to evaluate the protective efficacy of immunity by infection with a Japanese field isolate, EDRD1, against heterologous challenge with a Vietnamese HP-PRRSV field strain. To this end, four groups of PRRSV-negative crossbreed piglets were used for a challenge study. Groups 1 and 2 were inoculated with EDRD1 via the intranasal route. After 26 days, Groups 2 and 3 were inoculated with HP-PRRSV via the same route. Group 4 served as an uninfected control. Blood and oral fluid samples were taken every 3–4 days after HP-PRRSV challenge; on day 16 post-challenge, all pigs were euthanized, and examined pathologically.

Results

The nucleotide sequence analysis of nonstructural protein 2 gene of EDRD1 and comparison with Vietnamese HP-PRRSV showed that the 39 amino acid deletion sites of EDRD1 was nearly in the same region as the 29 amino acid deletion sites of HP-PRRSV. Immunity conferred by inoculation with EDRD1 dramatically reduced viral load in the sera and tissues besides viral shedding (Group 2) compared with those in pigs infected only with HP-PRRSV (Group 3). The clinical signs and rectal temperature were significantly reduced, and the average daily weight gain was significantly improved in the EDRD1-inoculated pigs (Group 2) compared with the Group 3 pigs. Notably, no viral RNA was detected in various organs of the Group 2 pigs 16 days post-infection with HP-PRRSV, except in one pig. Therefore, the immunity induced by EDRD1 and its genetically close field isolates may play a role in reducing viremia caused by HP-PRRSV.

Conclusions

The results of the present study demonstrate that pigs are highly protected against heterologous Vietnamese HP-PRRSV challenge by immunity against a Japanese local strain, EDRD1.

Genetic characterization of a new NSP2-deletion porcine reproductive and Respiratory Syndrome Virus in China

The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) cause a huge economic loss around the pig industry worldwide; the NADC30-like PRRSV have attracted much attention outbreaks in China in recent years. Recombination between PRRSV subtypes, point mutations, insertions and deletions that contribute to the emergence of new variants in the genome. In this study, the PRRSV-HB-16-China-2019 strain's full-length genomic sequence shares 93.0% nucleotide similarity to NADC30 PRRSV without any gene insertion. Compared with VR-2332, it has an NSP2 coding region that is different from NADC30, which has a discontinuous 206-aa (111-aa from position 323 to 433 and 95-aa from position 476 to 570) deletion. Compared with other NADC30-Like strains, it has a discontinuous 75-amino acid (75-aa from position 476 to 552) deletion, which was first reported. Notably, the strain, PRRSV-HB-16-China-2019, contained an addition a 1-aa deletion in ORF5 and a unique 3-nt deletion in 3'-UTR similar to NADC30, the strain is recombined between a NADC30-like strain and a vaccine strain named RespPRRS MLV(parental strain VR-2332). Our findings indicate that PRRSV-HB-16-China-2019 is a new NSP2-deletion NADC30-like strain with certain deletions and mutations. Our results show that the emergence of the new NADC30-like strain has increased the difficulty of PRRSV prevention in China.

Whole-Genome Sequencing of Porcine Reproductive and Respiratory Syndrome Virus from Field Clinical Samples Improves the Genomic Surveillance of the Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major economic concern worldwide. There are currently large data sets available about the ORF5 gene of the virus, with thousands of sequences available, but little data are currently available on the full-length genome of PRRSV. We hypothesized that whole-genome sequencing (WGS) of the PRRSV genome would allow better epidemiological monitoring than ORF5 gene sequencing. PRRSV PCR-positive serum, oral fluid, and tissue clinical samples submitted to the diagnostic laboratory for routine surveillance or diagnosis of PRRSV infection in Québec, Canada, swine herds were used. The PRRSV reverse transcription-quantitative PCR Cq values of the processed samples varied between 11.5 and 34.34. PRRSV strain genomes were isolated using a poly (A)-tail method and were sequenced with a MiSeq Illumina sequencer. Ninety-two full-length PRRSV genomes were obtained from 88 clinical samples out of 132 tested samples, resulting in a PRRSV WGS success rate of 66.67%. Three important deletions in ORF1a were found in most wild-type (i.e., not vaccine-like) strains. The importance of these deletions remains undetermined. Two different full-length PRRSV genomes were found in four different samples (three serum samples and one pool of tissues), suggesting a 4.55% PRRSV strain coinfection prevalence in swine. Moreover, six PRRSV whole genomes (6.52% of PRRSV strains) were found to cluster differently than they did under the ORF5 classification method. Overall, WGS of PRRSV enables better strain classification and/or interpretation of results in 9.10% of clinical samples than ORF5 sequencing, as well as allowing interesting research avenues.

Co-expression of self-cleaved multiple proteins derived from Porcine Reproductive and Respiratory Syndrome Virus by bi-cistronic and tri-cistronic DNA vaccines

Porcine Reproductive and Respiratory Syndrome caused by Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) remains one of the important diseases in swine industry. A vaccine that is safe, effective and also elicit broad immune response against multiple antigens is desirable. In this study, we developed multi-cistronic DNA vaccines capable of co-expressing multiple structural proteins derived from PRRSV. To preserve the structure and function of each antigen protein, we employed self-cleaving 2A peptides to mediate separation of multiple proteins expressed by multi-cistronic genes. Six bi-cistronic genes encoding PRRSV GP5 and M proteins were generated, by which each construct contains different 2A sequences derived from Foot-and-mouth disease virus (F2A), porcine teschovirus-1 (P2A) and Thosea asigna virus (T2A) either with or without furin cleavage site (Fu). Vectored by the mammalian expression plasmid pTH, all six bi-cistronic genes co-expressed the proteins GP5 and M at comparable level. Importantly, all six types of 2A sequences could mediate a complete self-cleavage of the GP5 and M. We next generated tri-cistronic DNA vaccines co-expressing the PRRSV proteins GP5, M and N. All homologous and heterologous combinations of P2A and F2A in tri-cistronic genes yielded a complete self-cleavage of the GP5, M and N proteins. Our study reports a success in co-expression of multiple PRRSV structural proteins in discrete form from a single vaccine and confirms feasibility of developing one single vaccine that provides broad immune responses against PRRSV.

Histopathological Lesions Accompanied with First-Time Isolation of a PRRSV-2 Strain in Greece

Genotype 2 strains of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV-2) have been reported sporadically in Europe. Even if, PRRSV-2 reported to be genetically homogenous in Europe due to the introduction of an MLV vaccine strain, independent introductions of PRRSV-2 field strains have been reported. The aim of the present study was to report the complete genome sequence and evaluate the histopathological lesions of a PRRSV-2 strain, isolated for the first time in Greece. During a routine blood sampling in a commercial pig farm, the results revealed positive samples in weaners of 40-60 days for the PRRSV-2, using real-time polymerase chain reaction. The clinical picture was characterized from respiratory symptoms in weaners, as well as coughing and poor performance at finishing stage and less than 3% mortality rate from weaning stage to finishing stage. The use of ORF5 for PRRSV phylogenetic analysis of the isolated PRRSV strain, named "x1544-1 strain", was successfully determined, belonging to the genotype PRRSV-2. Comparison of the obtained sequence revealed nucleotide sequence identity >98% with PRRSV-2 strain VR2332 and other related strains from Denmark and China. The histopathological evaluation revealed diffuse interstitial pneumonia, multifocal interstitial nephritis, while in the lymphoid organs, follicular and paracortical hyperplasia, coexisting with necrosis and depletion of germ cells were detected. The results of current study undersign the importance for veterinary practitioners to have up-to-date access to phylogenetic data linked to phenotypic information to follow-up the control and prevention strategies against PRRSV.

Development of a bead-based assay for detection and differentiation of field strains and four vaccine strains of type 2 porcine reproductive and respiratory syndrome virus (PRRSV-2) in the USA

Porcine reproductive and respiratory syndrome (PRRS) remains one of the most economically devastating diseases in swine population in the United States of America. Due to high mutation rate of the PRRS virus (PRRSV) genome, it is difficult to develop an accurate diagnostic assay with high strain coverage. Differentiation of field strains from the four vaccines that have been used in the USA, namely Ingelvac PRRS MLV, Ingelvac ATP, Fostera PRRS and Prime Pac PRRS, adds an additional challenge. It is difficult to use current real-time PCR systems to detect and differentiate the field strains from the vaccine strains. Luminex xTAG technology allows us to detect more molecular targets in a single reaction with a cost similar to a single real-time PCR reaction. By analysing all available 678 type 2 PRRSV (PRRSV-2) complete genome sequences, including the 4 vaccine strains, two pairs of detection primers were designed targeting the conserved regions of ORF4-ORF7, with strain coverage of 98.8% (670/678) based on in silico analysis. The virus strains sharing ≥98% identity of the complete genomes with the vaccine strains were considered vaccine or vaccine-like strains. One pair of primers for each vaccine strain were designed targeting the nsp2 region. In silico analysis showed the assay matched 94.7% (54/57) of Ingelvac PRRS^® MLV (MLV) strain and the MLV-like strains, and 100% of the other three vaccine strains. Analytical sensitivity of the Luminex assay was one to two logs lower than that of the reverse transcription real-time PCR assay. Evaluated with 417 PRRSV-2 positive clinical samples, 95% were detected by the Luminex assay. Compared to ORF5 sequencing results, the Luminex assay detected 92.4% (73/79) of MLV strains, 78.3% (18/23) of Fostera strains and 50% (2/4) of ATP strains. None of the 472 samples were the Prime Pac strain tested by either ORF5 sequencing or the Luminex assay.

Pathogenicity of porcine reproductive and respiratory syndrome virus (ORF5 RFLP 1-7-4 viruses) in China

Porcine reproductive and respiratory syndrome virus (PRRSV) is an RNA virus that causes reproductive failure in sows and respiratory problems in piglets. PRRSV infection leads to substantial pig mortality and causing huge economic losses so that disease outbreaks caused by the new PRRSV strain from other regions have caused great concern in China. In this study, we analysed the pathogenicity of the novel ORF5 RFLP 1-7-4-like PRRSV strain, named PRRSV-ZDXYL-China-2018-1 in pigs. The viral challenge test showed that PRRSV-ZDXYL-China-2018-1 infection can cause persistent fever, moderate dyspnoea, serum viraemia and interstitial pneumonia in piglets. The levels of viral loads in serum and PRRSV-specific antigen were also detected in lung tissues were used one-step Taq-Man RT-qPCR and Immunohistochemistry, respectively. At 28dpi, the level of specific antibodies was increased among infected piglets. Importantly, the new virus appeared be a moderately virulent isolate with pathogenicity compared to HP-PRRSV strain LQ (JXA1-like strain). Histological examination revealed severe monocyte haemorrhage and interstitial pneumonia associated with monocyte infiltration in the lung tissue of pigs infected with PRRSV-ZDXYL-China-2018-1 and LQ-JXA1 strains. Immunohistochemistry (IHC) results showed positive brown-red epithelial cells and macrophages in pig lungs. Therefore, it is critical to establish an effective strategy to control the spread of PRRSV in China.

Studies on heterologous protection between Japanese type 1 and type 2 porcine reproductive and respiratory syndrome virus isolates

The objective of the present study was to evaluate the cross-protective immunity between type 1 and type 2 porcine reproductive and respiratory syndrome virus (PRRSV) isolates in growing pigs. Japanese type 1 PRRSV, first isolated from a pig with respiratory disorders in a farm in 2009, exhibits unique genetic characteristics. The pathogenicity of a Japanese standard strain of type 2 PRRSV, EDRD1, in pigs immunized by the type 1 PRRSV isolate, Jpn EU 4-37 was determined by evaluating clinical signs, viremia, antibody response, and pathological lesions. Similarly, we evaluated the pathogenicity of Jpn EU 4-37 in pigs immunized by EDRD1 and compared the cross-protective immunity between these isolates. The EDRD1 challenge after Jpn EU 4-37 inoculation reduced viral clearance and shedding in pigs, compared to those treated with the EDRD1 single infection. On the other hand, the pathogenicity of Jpn EU 4-37 after EDRD1 infection did not differ significantly compared to non-immunized pigs treated with Jpn EU 4-37. Therefore, exposure to Jpn EU 4-37 could not induce enough immunity to reduce the viremia against subsequent infection by type 2 PRRSV. However, the immunity induced by Jpn EU 4-37 infection may play a role in reducing viremia caused by type 2 PRRSV. Moreover, the immunity induced by the EDRD1 and other genetically related viruses, which are broadly distributed in Japan, may not contribute to cross-protection against Jpn EU 4-37 as an emerging virus.

A potential endemic strain in China: NADC34-like porcine reproductive and respiratory syndrome virus

Porcine respiratory and reproductive syndrome virus (PRRSV) causes an economically important disease affecting commercial pork production worldwide. NADC34-like PRRSV has had a strong impact on the U.S. and Peruvian pig industries in recent years and also emerged in northeastern China in 2017. However, the endemic status of NADC34-like PRRSV in China is unclear. In this study, we examined 650 tissue samples collected from 16 Provinces in China from 2018 to 2019. Six NADC34-like PRRSV strains were detected in samples from three Provinces, and the complete genomes of four of these strains were sequenced. Phylogenetic analysis showed that these novel PRRSV strains belong to sublineage 1.5 (or NADC34-like PRRSV), forming two groups in China. Sequence alignment suggested that these novel strains share the same 100-aa deletion in the Nsp2 protein that was identified in IA/2014/NADC34 isolated from the United States in 2014. Recombination analysis revealed that five of eight complete genome sequences are derived from recombination between IA/2014/NADC34 and ISU30 or NADC30. The number and distribution of NADC34-like PRRSVs is increasing in China. Importantly, compared with the currently endemic strain NADC30-like PRRSV, NADC34-like PRRSV has the potential to be an endemic strain in China. This study will help us understand the epidemic status of NADC34-like PRRSV in China and provide data for further monitoring this type of PRRSV in China.

Outbreak of Porcine Reproductive and Respiratory Syndrome Virus 1 in Taiwan

Porcine reproductive and respiratory syndrome (PRRS) causes significant economic losses in the swine industry worldwide. The PRRS virus (PRRSV) can be divided into two species, PRRSV 1 (European) and PRRSV 2 (North American). In Taiwan, PRRSV 2 isolates are dominant and cause respiratory symptoms in nursing pigs. From October to November 2018, in a pig herd in central Taiwan, pregnant sows had abortions and stillbirths, and piglets suffered from respiratory disorders. Laboratory tests identified the presence of PRRSV 1 in serum from sows and suckling piglets in this scenario. The complete genome of the identified PRRSV 1 strain was genetically closely related to that of a European PRRSV vaccine strain (98.2%). This local European isolate is designated as PRRSV/NPUST-2789-3W-2/TW/2018 (NPUST2789). This report is the first to indicate an outbreak in Taiwan of a PRRSV 1 strain that shares a common evolutionary ancestor with the European PRRSV vaccine strain.

The Nsp12-coding region of type 2 PRRSV is required for viral subgenomic mRNA synthesis

As one of many nonstructural proteins of porcine reproductive and respiratory syndrome virus (PRRSV), nonstructural protein 12 (Nsp12) has received relatively little attention, and its role in virus replication, if any, is essentially unknown. By the application of reverse genetic manipulation of an infectious PRRSV clone, the current study is the first to demonstrate that Nsp12 is a key component of PRRSV replication. In addition, the biochemical properties of Nsp12 were evaluated, revealing that Nsp12 forms dimers when exposed to oxidative conditions. Furthermore, we systemically analyzed the function of Nsp12 in PRRSV RNA synthesis using a strand-specific PCR method. To our surprise, Nsp12 was not found to be involved in minus-strand genomic RNA (-gRNA) synthesis; importantly, our results indicate that Nsp12 is involved in the synthesis of both plus- and minus-strand subgenomic mRNAs (+sgmRNA and -sgmRNA). Finally, we found that the combination of cysteine 35 and cysteine 79 in Nsp12 is required for sgmRNA synthesis. To our knowledge, we are the first to report the biological role of Nsp12 in the PRRSV lifecycle, and we conclude that Nsp12 is involved in the synthesis of both + sgRNA and -sgRNA.

A comparison of two commercially available porcine reproductive and respiratory syndrome virus (PRRSV) modified-live virus vaccines analyzing the growth performance in 1-day-old vaccinated swine located on endemic farms co-circulating PRRSV-1 and PRRSV-2

The objective of this study was to compare the efficacy of a porcine reproductive and respiratory syndrome virus (PRRSV)-1 and PRRSV-2 modified-live virus (MLV) vaccines when administered at 1 day of age under field conditions. The piglets elicited anti-PRRSV antibodies at 1 day of age even in the presence of maternally derived antibodies. The number of PRRSV-2 genomic copies in the sera of pigs from the PRRSV-2 MLV-vaccinated pigs was significantly (P<0.05) lower when compared to PRRSV-1 MLV-vaccinated pigs. The average daily gain in PRRSV-2 MLV-vaccinated pigs was significantly (P<0.05) higher when compared to both PRRSV-1 MLV-vaccinated and unvaccinated pigs. This study demonstrated that vaccination as early as 1 day of age was effective against PRRSV infection.

Simultaneous detection of classical PRRSV, highly pathogenic PRRSV and NADC30-like PRRSV by TaqMan probe real-time PCR

Porcine Reproductive and Respiratory Syndrome (PRRS), an acute infectious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV), is one of the most devastating diseases affecting the global swine industry. In order to establish a multiplex real-time PCR method for the simultaneous detection of the classical PRRSV (C-PRRSV) strain, the highly pathogenic PRRSV (HP-PRRSV) strain and NADC30-like PRRSV (NL-PRRSV) strain, we designed specific primers and TaqMan fluorescent probes based on the Nsp2 target gene sequence of these three different PRRSV strains, and designed American-type PRRSV (PRRSV-U) special primers and probes based on the relatively conserved target gene sequence of ORF7. The method established in this study can quickly and accurately detect and differentiate three types of strains of clinical tissue samples, respectively. This method plays a key role in the rapid diagnosis and determination of PRRSV.

Antiviral effect of 25-hydroxycholesterol against porcine reproductive and respiratory syndrome virus in vitro

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that causes economically huge losses to the pig industry worldwide. Current control of PRRSV infection remains inadequate although various means have been implemented. Thus, investigating novel antiviral therapeutics to combat PRRSV infection is essential. In the present study, the antiviral effect in vitro of 25-hydroxycholesterol (25HC) against PRRSV was investigated.

METHODS

Cell viability assay was performed to examine the impact of 25HC on the cell viability. Indirect immunofluorescence assay and virus titration were utilized to evaluate the levels of PRRSV growth. Viral attachment assay, penetration assay and release assay were conducted to investigate the antiviral mechanism of 25HC against PRRSV. Real-time RT-PCR assay was used to analyse the effect of 25HC on the genome synthesis of PRRSV.

RESULTS

We demonstrated that the growth of PRRSV was significantly inhibited in 25HC-pretreated cells and PRRSV-infected cells by 25HC. Moreover, 25HC could impair the attachment and entry of PRRSV in vitro, but not affect viral genome synthesis and virion release.

CONCLUSIONS

Our findings clearly indicate that 25HC can exert antiviral effect against PRRSV infection in vitro, suggesting that 25HC might be a novel potential agent to control PRRSV infection.

High-frequency mutation and recombination are responsible for the emergence of novel porcine reproductive and respiratory syndrome virus in northwest China

Porcine reproductive and respiratory syndrome (PRRS) is one of the most highly infectious diseases in the pig industry, resulting in enormous economic losses worldwide. In this study, a PRRS virus (PRRSV) strain was isolated from primary porcine alveolar macrophage cells in Xinjiang in northwest China. This new strain was sequenced and designated as XJzx1-2015, and its sequence was then compared to those of other representative PRRSV strains from around the world. Complete genomic characterisation showed that the full-length nucleotide sequence of XJzx1-2015 exhibited low-level similarity to NB/04 (91.6%), JXA1 (90.5%), CH-1a (90.2%), VR-2332 (86.9%), QYYZ (85.7%), and JL580 (82.2%), with the highest similarity to HK13 (91.7%) sequence identity. Nonstructural protein 2 (NSP2) and glycosylated protein (GP) 2 of XJzx1-2015 had deletions of five and two amino acids, respectively, corresponding to strain VR-2332 positions 475-479 and 173-174. Phylogenetic analysis based on complete genome sequences showed that XJzx1-2015 and four other strains from China formed a new subgenotype closely related to other sublineage 8.7 (JXA1-like) strains belonging to the North American genotype. However, phylogenetic analysis based on NSP2 and GP5 showed that XJzx1-2015 clustered with sublineage 8.7 (JXA1-like, CH-1a-like) and lineage 3 (QYYZ-like) strains, respectively. Recombination analysis indicated that XJzx1-2015 is an intersubgenotype recombinant of CH-1a-like and QYYZ-like strains. Overall, our findings demonstrate that XJzx1-2015 is a novel PRRSV strain with a significantly high frequency of mutation and a recombinant between lineage 3 and sublineage 8.7 identified in northwest China. These results provide important insights into PRRSV evolution.

Simulation of control scenarios of porcine reproductive and respiratory syndrome in Nghe An Province in Vietnam

The main objective of this study was to develop various models using North American Animal Disease Spread Model (NAADSM) to simulate the transmission of Porcine reproductive and respiratory syndrome (PRRS) virus between farms in Nghe An Province in Vietnam in order to inform the prevention and control of this important disease. Using real data from the household survey, credible parameters for direct/indirect mean contact rates between different farms were estimated. A total of eleven models were developed, including immunization scenarios. In addition, we conducted sensitive analysis on how the mean contact rates influenced the results. The immunization scenarios showed that a high proportion of pigs in medium size farms needs to be vaccinated in order to reduce the transmission to pigs in small farms under the Vietnamese pig production system. In order to promote the use of vaccinations, incentives (such as a vaccine subsidy) for medium size farms may be needed. It could be the most cost-effective control and prevention strategy for pig diseases in Vietnam. Our study provides insights on how pig diseases can be spread between pig farms via direct and indirect contact in Nghe An under the various hypothetical scenarios. Our results suggest that medium/large farms may play an important role in the transmission of pig diseases.

Emergence of a virulent porcine reproductive and respiratory syndrome virus in Taiwan in 2018

In March 2018, an abortion storm caused by porcine reproductive and respiratory syndrome virus was confirmed in a farrow‐to‐finish pig herd in Taiwan. Open reading frame 5 and non‐structural protein 2 of the virus confirmed that the virus is closely related to the virulent strains circulating in the United States.

Emergence of two novel recombinant porcine reproductive and respiratory syndrome viruses 2 (lineage 3) in Southwestern China

The lineage 3 of porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) was first reported in mainland China in 2010 and it has spread rapidly in recent years. Here, two novel lineage 3 strains of PRRSV-2 were isolated from diseased pigs in Southwestern China during 2017-2018, and were designated as GZgy17 and SCya18. The complete genomes of the two isolates were then determined, and sequence alignment revealed that GZgy17 had the same discontinuous 30-amino acid (aa) deletion in NSP2 as JXA1, while SCya18 contained the discontinuous 131-aa deletion in NSP2 identical to that of NADC30, when compared to the strain VR-2332. Notably, GZgy17 contained an additional 19-aa deletion in NSP2, and SCya18 had a unique 3-nt deletion in its 3'UTR. Homology and phylogenetic analysis showed that GZgy17 and SCya18 shared low nucleotide homology (91.2-92.0%) with QYYZ and were classified into a new cluster of lineage 3 strains based on ORF5 genotyping. Recombination analyses revealed that GZgy17 and SCya18 both originated from a SH/CH/2016-like (lineage 3) strain and had recombined with a JXA1-like (lineage 8) and a NADC30-like (lineage 1) strain, respectively. Furthermore, we compared the virulence of the two strains in 4-week-old piglets. The results showed that GZgy17 caused mortality rates of 20% and exhibited higher pathogenicity in piglets compared to SCya18. Our findings suggest that recombination might be responsible for the variations in pathogenicity of lineage 3 strains of PRRSV-2 and highlight the importance of surveillance of this lineage in China.

A comparative study of the efficacy of a porcine reproductive and respiratory syndrome subunit and a modified-live virus vaccine against respiratory diseases in endemic farms

The efficacy of a porcine reproductive and respiratory syndrome (PRRS) subunit vaccine was evaluated and compared with a modified-live virus (MLV) vaccine under field conditions. Three farms were selected based on their history of respiratory diseases caused by co-infection with both PRRSV-1 and PRRSV-2. In each farm, 60 pigs were randomly allocated to 2 vaccinated and 1 unvaccinated groups (20 pigs per group). One group of pigs were administered the PRRS subunit vaccine at 21 and 42 days of age and another group administered the PRRS MLV vaccine at 21 days of age. The subunit vaccine had similar efficacy and, in some instances, performed even better than the MLV vaccine. Vaccination of pigs with either of the PRRS vaccines resulted in significantly improved growth performance in Farm B but not in Farm C. In Farm A, pigs vaccinated with the PRRS subunit vaccine had a better growth performance statistically compared to those vaccinated with the PRRS MLV vaccine. At the peak of PRRSV-1 and PRRSV-2 viremia, neutralizing antibodies and T-cell responses against PRRSV-1 and PRRSV-2 were at low levels suggesting that either vaccine is only able to provide a partial protection against co-circulating PRRSV-1 and PRRSV-2.

Evaluation of the Inhibitory Effects of (E)-1-(2-hydroxy-4,6-dimethoxyphenyl)-3-(naphthalen-1-yl)prop-2-en-1-one (DiNap), a Natural Product Analog, on the Replication of Type 2 PRRSV In Vitro and In Vivo

DiNap [(E)-1-(2-hydroxy-4,6-dimethoxyphenyl)-3-(naphthalen-1-yl)prop-2-en-1-one], an analog of a natural product (the chalcone flavokawain), was synthesized and characterized in this study. Porcine reproductive and respiratory syndrome virus (PRRSV) is the most challenging threat to the swine industry worldwide. Currently, commercially available vaccines are ineffective for controlling porcine reproductive and respiratory syndrome (PRRS) in pigs. Therefore, a pharmacological intervention may represent an alternative control measure for PRRSV infection. Hence, the present study evaluated the effects of DiNap on the replication of VR2332 (a prototype strain of type 2 PRRSV). Initially, in vitro antiviral assays against VR2332 were performed in MARC-145 cells and porcine alveolar macrophages (PAMs). Following this, a pilot study was conducted in a pig model to demonstrate the effects of DiNap following VR2332 infection. DiNap inhibited VR2332 replication in both cell lines in a dose-dependent manner, and viral growth was completely suppressed at concentrations ≥0.06 mM, without significant cytotoxicity. Consistent with these findings, in the pig study, DiNap also reduced viral loads in the serum and lungs and enhanced the weight gain of pigs following VR2332 infection, as indicated by comparison of the DiNap-treated groups to the untreated control (NC) group. In addition, DiNap-treated pigs had fewer gross and microscopic lesions in their lungs than NC pigs. Notably, virus transmission was also delayed by approximately 1 week in uninfected contact pigs within the same group after treatment with DiNap. Taken together, these results suggest that DiNap has potential anti-PRRSV activity and could be useful as a prophylactic or post-exposure treatment drug to control PRRSV infection in pigs.

Seasonal patterns and space-time clustering of porcine reproductive and respiratory syndrome (PRRS) cases from 2008 to 2016 in Vietnam

Porcine reproductive and respiratory syndrome (PRRS) is an important disease in pig production and is endemic in Vietnam. No nationwide studies have been carried out to understand the spread of PRRS in Vietnam. The main objective of this study was to identify the seasonal patterns and space‐time clusters of PRRS from 2008 to 2016 using national surveillance data in Vietnam. A total of 614,219 cases were reported during the period. There was a seasonal pattern with single peak by region (except North Central Coast, showing double peaks in March and June). The seasonal plots from the Northern regions showed a higher peak between March and April, whereas the four regions from Southern part displayed a higher peak between June and August. Overall, outbreaks from the northern part of Vietnam tended to occur 3–4 months earlier than the southern part. When the spatial window was set at 50%, space‐time cluster analysis found that the first cluster occurred in the Red River Delta (RRD) (radius: 82.17 km; ratios: 5.5; period: Mar–May/2010) and the second (radius: 50.8 km; ratios: 10.61; period: Aug–Oct/2011) in the Mekong River Delta (MRD) region. Four other clusters were observed in the central and Southern parts. Our findings might provide better insight into the distribution of clusters and temporal patterns of PRRS in Vietnam. This study may provide policy makers with valuable information on the hotspot areas and timing of outbreaks. Also, it identifies when and where national control program could be implemented more efficiently by targeting resources for the prevention and control of PRRS.

Porcine endogenous retrovirus envelope coated baculoviral DNA vaccine against porcine reproductive and respiratory syndrome virus

PERV is a major virus concerning xenotransplantation study. However, the interesting part is that PERV is present in all kinds of pigs without pathogenicity and immune response. Furthermore, since pig cells have receptors for PERV, the gene delivery system using PERV envelope is highly likely to develop into an excellent viral vector in pigs. We developed a recombinant baculovirus with a modified surface for expressing the porcine endogenous retrovirus (PERV) envelope. Porcine reproductive and respiratory syndrome virus (PRRSV) infection is a severe concern in the porcine industry due to reproduction failure and respiratory symptoms. GP5 and M proteins are major immunogenic proteins of PRRSV. Using PERV-modified baculovirus (Ac mPERV) as a delivery vector, we constructed a dual antigen (GP5 and M)-encoding DNA vaccine system, Ac mPERV-C5/C6. Intramuscular immunization in mice and pigs, Ac mPERV-C5/C6 induced comparative high humoral and cellular immune responses. Our results support further development of Ac mPERV-C5/C6 as a potential PRRSV vaccine in the porcine industry. In addition, the Ac mPERV system may be applied to the generation of other effective DNA vaccines against porcine viral diseases.

Co-administration of saponin quil A and PRRSV-1 modified-live virus vaccine up-regulates gene expression of type I interferon-regulated gene, type I and II interferon, and inflammatory cytokines and reduces viremia in response to PRRSV-2 challenge

Porcine reproductive and respiratory syndrome virus (PRRSV) is a devastating virus which suppresses the expression of type I and II interferons (IFNs) as well as several pro-inflammatory cytokines. Our previous study reported that saponin quil A had a potential to up-regulate the expression of type I IFN-regulated genes and type I and II IFNs in porcine peripheral blood mononuclear cells (PBMC) inoculated with PRRSV. The present study evaluated the immunostimulatory effect of quil A on potentiating cross protective immunity of PRRSV-1 modified-live virus (MLV) vaccine against PRRSV-2 challenge. Twenty-four 4-week-old PRRSV-seronegative pigs were divided into four groups of six pigs. Group 1 and group 2 pigs were vaccinated with PRRSV-1 MLV vaccine at 0 dpv (day post vaccination), and additionally group 2 pigs were injected intramuscularly with quil A at -1, 0, 1 dpv. Group 3 pigs were injected with PRRSV-1 MLV vaccine solvent at 0 dpv and served as challenge control, while group 4 pigs served as strict control. Group 1-3 pigs were challenged intranasally with PRRSV-2 at 28 dpv and immune and clinical parameters were observed from 0 until 49 dpv. Group 1 pigs showed significantly reduced PRRSV viremia, number of viremic pigs, and clinical scores, and significantly improved average daily weight gain (ADWG), compared to group 3 pigs. Group 2 pigs showed significantly increased mRNA expressions of interferon regulatory factor 3, 2'-5'-oligoadenylatesynthetase 1, osteopontin, IFNα, IFNβ, IFNγ, interleukin-2 (IL-2), IL-13 and tumor necrosis factor alpha, compared to group 1 pigs. The animals demonstrated significantly reduced PRRSV viremia and number of viremic pigs, but did not demonstrate any further improved PRRSV-specific antibody levels, neutralizing antibody titers, rectal temperature, clinical scores, and ADWG as compared to group 1 pigs. Our findings suggest that quil A up-regulates type I IFN-regulated gene, type I and II IFNs, and inflammatory cytokine expressions which may contribute to further reducing PRRSV viremia and number of viremic pigs which were conferred by PRRSV-1 MLV vaccine. Our findings also suggest that quil A may serve as an effective immunostimulator for potentiating cell-mediated immune defense to PRRSV.

Independent evolution of porcine reproductive and respiratory syndrome virus 2 with genetic heterogeneity in antigenic regions of structural proteins in Korea

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen that affects the global swine industry. The continuous evolution of this virus has made control and prevention difficult, which emphasizes the importance of monitoring currently circulating PRRSV strains. In this study, we investigated the genetic characteristics of whole structural genes of 35 PRRSV-2 isolates that circulated between 2012 and 2017 in Korea. Genetic and phylogenetic analysis demonstrated that a recently identified PRRSV-2 shared a relatively low level of nucleotide sequence identity that ranged from 86.2% to 92.8%; however, they were clustered into four distinct Korean field clades, except KU-N1702, in ORF2-7-based phylogeny. KU-N1702 was closely related to the NADC30-like strains that were identified in the USA and China. Amino acid sequence analysis showed that the GP5 neutralizing epitope was conserved among the KU viruses. In contrast, the viruses had genetic mutations in key residues for viral neutralization within GP5 and M. For minor structural proteins, neutralizing epitopes, aa 41-55 of GP2, 61-75 of GP3, and 51-65 of GP4, were variable among the KU viruses. Bioinformatics demonstrated diversifying evolution within the GP2 and GP4 neutralizing epitopes and the emergence of a novel glycosylation site within the GP3 and GP4 neutralizing epitopes. Taken together, these data provide evidence that Korean PRRSV-2 evolved independently in Korea, with genetic heterogeneity in antigenic regions of structural proteins.

Genetic Characterization and Pathogenicity of a Novel Recombined Porcine Reproductive and Respiratory Syndrome Virus 2 among Nadc30-Like, Jxa1-Like, and Mlv-Like Strains

Recombination among porcine reproductive and respiratory syndrome viruses (PRRSVs), coupled with point mutations, insertions, and deletions occurring in the genome, is considered to contribute to the emergence of new variants. Here, we report the complete genome sequences of a PRRSV field strain, designated SCN17, isolated from a RespPRRS MLV-vaccinated piglet in China in 2017. Sequence alignment revealed that SCN17 had discontinuous 131-amino acid (111 + 1 + 19-aa) deletion in the NSP2-coding region identical to that of NADC30 when compared to VR-2332. Notably, the strain, SCN17, contained an additional 1-aa deletion in NSP2, a 1-aa deletion in ORF5, and a unique 3-nt deletion in the 3′-UTR. Phylogenetic analysis showed that SCN17 clustered into NADC30-like lineage based on ORF5 genotyping, whereas it belonged to an inter-lineage between the NADC30-like and VR-2332-like lineages as established based on the full-length genome. Importantly, the SCN17 was identified as a novel virus recombined between a NADC30-like (moderately pathogenic), a JXA1-like (highly pathogenic), and an attenuated vaccine strain, RespPRRS MLV (parental strain VR-2332). Furthermore, we tested its pathogenicity in piglets. SCN17 infection caused a persistent fever, moderate interstitial pneumonia, and increased the viremia and antibody levels in the inoculated piglets. Of note, all SCN17-infected piglets survived throughout the study. The new virus was showed to be a moderately virulent isolate and have lower pathogenicity than HP-PRRSV strain, SCwhn09CD. Our results provide evidence for the continuing evolution of PRRSV field strain by genetic recombination and mutation leading to outbreaks in the vaccinated pig populations in China.

A new recombined porcine reproductive and respiratory syndrome virus virulent strain in China

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important swine diseases worldwide. In the present study, a new virulent strain of PRRS virus (PRRSV), GDsg, was isolated in Guangdong province, China, and caused high fever, high morbidity, and high mortality in sows and piglets. The genome of this new strain was 15,413 nucleotides (nt) long, and comparative analysis revealed that GDsg shared 82.4% to 94% identity with type 2 PRRSV strains, but only 61.5% identity with type 1 PRRSV Lelystad virus strain. Phylogenetic analysis indicated that type 2 PRRSV isolates include five subgenotypes (I, II, III, IV, and V), which are represented by NADC30, VR-2332, GM2, CH-1a, and HuN4, respectively. Moreover, GDsg belongs to a newly emerging type 2 PRRSV subgenotype III. More interestingly, the newly isolated GDsg strain has multiple discontinuous nt deletions, 131 (19 + 18 + 94) at position 1404–1540 and a 107 nt insertion in the NSP2 region. Most importantly, the GDsg strain was identified as a virus recombined between low pathogenic field strain QYYZ and vaccine strain JXA1-P80. In conclusion, a new independent subgenotype and recombinant PRRSV strain has emerged in China and could be a new threat to the swine industry of China.

Whole Genome Analysis of Two Novel Type 2 Porcine Reproductive and Respiratory Syndrome Viruses with Complex Genome Recombination between Lineage 8, 3, and 1 Strains Identified in Southwestern China

Recombination among porcine reproductive and respiratory syndrome viruses (PRRSVs) is thought to contribute to the emergence of new PRRSV variants. In this study, two newly emerged PRRSV strains, designated SCcd16 and SCya17, are isolated from lung tissues of piglets in Southwestern China. Genome comparative analysis reveals that SCcd16/SCya17 exhibit 93.1%/93.2%, 86.9%/87.0%, 85.3%/85.7%, and 83.6%/82.0% nucleotide similarity to PRRSVs JXA1, VR-2332, QYYZ and NADC30, respectively. They only exhibit 44.8%/45.1% sequence identity with LV (PRRSV-1), indicating that both emergent strains belong to the PRRSV-2 genotype. Genomic sequence alignment shows that SCcd16 and SCya17 have the same discontinuous 30-amino acid (aa) deletion in Nsp2 of the highly pathogenic Chinese PRRSV strain JXA1, when compared to strain VR-2332. Notably, SCya17 shows a unique 5-nt deletion in its 3&rsquo;-UTR. Phylogenetic analysis shows that both of the isolates are classified in the QYYZ-like lineage based on ORF5 genotyping, whereas they appear to constitute an inter-lineage between JXA1-like and QYYZ-like lineages based on their genomic sequences. Furthermore, recombination analyses reveal that the two newly emerged PRRSV isolates share the same novel recombination pattern. They have both likely originated from multiple recombination events between lineage 8 (JXA1-like), lineage 1 (NADC30-like), and lineage 3 (QYYZ-like) strains that have circulated in China recently. The genomic data from SCcd16 and SCya17 indicate that there is on going evolution of PRRSV field strains through genetic recombination, leading to outbreaks in the pig populations in Southwestern China.

Plant synthetic GP4 and GP5 proteins from porcine reproductive and respiratory syndrome virus elicit immune responses in pigs

We demonstrated successful overexpression of porcine reproductive and respiratory syndrome virus (PRRSV)-derived GP4D and GP5D antigenic proteins in Arabidopsis. Pigs immunized with transgenic plants expressing GP4D and GP5D proteins generated both humoral and cellular immune responses to PRRSV. Porcine reproductive and respiratory syndrome virus (PRRSV) causes PRRS, the most economically significant disease affecting the swine industry worldwide. However, current commercial PRRSV vaccines (killed virus or modified live vaccines) show poor efficacy and safety due to concerns such as reversion of virus to wild type and lack of cross protection. To overcome these problems, plants are considered a promising alternative to conventional platforms and as a vehicle for large-scale production of recombinant proteins. Here, we demonstrate successful production of recombinant protein vaccine by expressing codon-optimized and transmembrane-deleted recombinant glycoproteins (GP4D and GP5D) from PRRSV in planta. We generated transgenic Arabidopsis plants expressing GP4D and GP5D proteins as candidate antigens. To examine immunogenicity, pigs were fed transgenic Arabidopsis leaves expressing the GP4D and GP5D antigens (three times at 2-week intervals) and then challenged with PRRSV at 6-week post-initial treatment. Immunized pigs showed significantly lower lung lesion scores and reduced viremia and viral loads in the lung than pigs fed Arabidopsis leaves expressing mYFP (control). Immunized pigs also had higher titers of PRRSV-specific antibodies and significantly higher levels of pro-inflammatory cytokines (TNF-α and IL-12). Furthermore, the numbers of IFN-γ⁺-producing cells were higher, and those of regulatory T cells were lower, in GP4D and GP5D immunized pigs than in control pigs. Thus, plant-derived GP4D and GP5D proteins provide an alternative platform for producing an effective subunit vaccine against PRRSV.

A novel HRM assay for differentiating classical strains and highly pathogenic strains of type 2 porcine reproductive and respiratory syndrome virus

Differentiation of classical strains and highly pathogenic strains of porcine reproductive and respiratory syndrome virus is crucial for effective vaccination programs and epidemiological studies. We used nested PCR and high resolution melting curve analysis with unlabeled probe to distinguish between the classical and the highly pathogenic strains of this virus. Two sets of primers and a 20 bp unlabeled probe were designed from the NSP3 gene. The unlabeled probe included two mutations specific for the classical and highly pathogenic strains of the virus. An additional primer set from the NSP2 gene of the highly pathogenic vaccine strain JXA1-R was used to detect its exclusive single nucleotide polymorphism. We tested 107 clinical samples, 21 clinical samples were positive for PRRSV (consistent with conventional PCR assay), among them four were positive for the classical strain with the remainder 17 for the highly pathogenic strain. Around 10 °C difference between probe melting temperatures showed the high discriminatory power of this method. Among highly pathogenic positive samples, three samples were determined as positive for JXA1-R vaccine-related strain with a 95% genotype confidence percentage. All these genotyping results using the high resolution melting curve assay were confirmed with DNA sequencing. This unlabeled probe method provides an alternative means to differentiate the classical strains from the highly pathogenic porcine reproductive and respiratory syndrome virus strains rapidly and accurately.

Identification of a Novel Recombinant Type 2 Porcine Reproductive and Respiratory Syndrome Virus in China

Since the emergence of NADC30-like porcine reproductive and respiratory syndrome virus (PRRSV) in China in 2013, PRRSVs have undergone rapid evolution. In this study, a novel variant of PRRSV strain (designated SCcd17) was successfully isolated from piglets with clinical signs in Sichuan Province in China in 2017, and the complete genomic sequence was determined. The genome of this new isolate was 15,015 nucleotides (nt) long, and comparative analysis revealed that SCcd17 exhibited 90.2%, 85.2%, 84.9%, and 84.0% nucleotide similarity to PRRSVs NADC30, JXA1, CH-1a, and VR-2332, respectively. Phylogenetic analysis indicated that the SCcd17 strain was classified into the NADC30-like sub-genotype, in which all the strains contained the unique discontinuous 131-amino acid deletion in nonstructural protein 2 (nsp2) when compared to VR-2332-like viruses. Notably, extensive amino acid substitutions were observed in nsp2 and a unique single amino acid deletion at position 33 of the GP5 is being described for the first time. Strikingly, recombination analysis revealed that SCcd17 was the result of recombination between the NADC30-like, JXA1-like, and VR-2332-like strains at five recombination breakpoints: nsp1α (nt 641), nsp3 (nt 5141), nsp10 (nt 9521), open reading frame 3 (ORF3) (nt 12,581), and ORF4 (nt 13,021). The genomic data of SCcd17 will be helpful for understanding the role of genomic recombination in the evolution of PRRSV.

Nonstructural protein 9 residues 586 and 592 are critical sites in determining the replication efficiency and fatal virulence of the Chinese highly pathogenic porcine reproductive and respiratory syndrome virus

The highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has caused huge economic losses to the swine industry in China. Understanding the molecular basis in relation to the virulence of HP-PRRSV is essential for effectively controlling clinical infection and disease. In the current study, we constructed and rescued a serial of mutant viruses in nsp9 and nsp10 based on the differential amino acid sites between HP-PRRSV JXwn06 and LP-PRRSV HB-1/3.9. The replication efficiency in pulmonary alveolar macrophages (PAMs) and the pathogenicity of the mutant viruses for piglets were analyzed. Our results showed that the mutation of Thr to Ala in 586 and Ser to Thr in 592 of nsp9 decreased the replication efficiency of HP-PRRSV in PAMs, and could attenuate its virulence for piglets, suggesting that the residues 586 and 592 of nsp9 are critical sites natively in determining the fatal virulence of the Chinese HP-PRRSV for piglets.

CD163 knockout pigs are fully resistant to highly pathogenic porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) causes severe economic losses to current swine production worldwide. Highly pathogenic PRRSV (HP-PRRSV), originated from a genotype 2 PRRSV, is more virulent than classical PRRSV and further exacerbates the economic impact. HP-PRRSV has become the predominant circulating field strain in China since 2006. CD163 is a cellular receptor for PRRSV. The depletion of CD163 whole protein or SRCR5 region (interaction site for the virus) confers resistance to infection of several PRRSV isolates in pigs or cultured host cells. In this study, we described the generation of a CD163 knockout (KO) pig in which the CD163 protein was ablated by using CRISPR/Cas9 gene targeting and somatic cell nuclear transfer (SCNT) technologies. Challenge with HP-PRRSV TP strain showed that CD163 KO pigs are completely resistant to viral infection manifested by the absence of viremia, antibody response, high fever or any other PRRS-associated clinical signs. By comparison, wild-type (WT) controls displayed typical signs of PRRSV infection and died within 2 weeks after infection. Deletion of CD163 showed no adverse effects to the macrophages on immunophenotyping and biological activity as hemoglobin-haptoglobin scavenger. The results demonstrated that CD163 knockout confers full resistance to HP-PRRSV infection to pigs without impairing the biological function associated with the gene.