Temporal lineage dynamics of the ORF5 gene of porcine reproductive and respiratory syndrome virus in Korea in 2014-2019.

Porcine reproductive and respiratory syndrome virus (PRRSV) is the most important pathogen in the Korean swine industry. Despite efforts including improved biosecurity and vaccination protocols, the virus continues to circulate and evolve. Based on phylogenetic analysis of open reading frame 5 (ORF5), Korean PRRSVs are known to form not only globally circulating lineages but also country-specific lineages (Lin Kor A, B, and C). To understand the recent epidemiological status of PRRSV in Korea, a total of 1349 ORF5 sequences of Korean PRRSV isolates from 2014 to 2019 were analyzed. Phylogenetic analysis was conducted using the maximum-likelihood method, and temporal changes in the relative prevalence of lineages were investigated. The analysis showed that PRRSV1 and PRRSV2 were both highly prevalent throughout the years examined. Among the PRRSV1 isolates, subgroup A (90.1%) and vaccine-like subgroup C (9.0%) composed most of the population. For PRRSV2 isolates, vaccine-like lineage 5 (36.3%) was dominant, followed by Lin Kor B (25.9%), Kor C (16.6%), lineage 1 (11.6%), and Kor A (9.1%). The PRRSV2 lineage 1 population increased from 2014 (1.8%) to 2019 (29.6%) in Korea due to the continual spread of sublineage 1.8 (NADC30-like) and introduction of sublineage 1.6 into the country. Additional genetic analysis, including analysis of non synonymous and synonymous mutations, revealed evidence of diversification and positive selection in immunologically important regions of the genome, suggesting that current vaccination is failing and promoting immune-mediated selection. Overall, these findings provide insights into the epidemiological and evolutionary dynamics of cocirculating viral lineages, and constant surveillance of PRRSV occurrence is needed.

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

BACKGROUND: Porcine reproductive and respiratory syndrome virus (PRRSV) infection can cause severe reproductive failure in sows and respiratory distress in pigs of all ages, leading to major economic losses. To date, there are still no effective strategies to prevent and control PRRSV. Antibody-dependent enhancement (ADE), a phenomenon in which preexisting non-neutralizing antibodies or sub-neutralizing antibodies facilitate virus entry and replication, may be a significant obstacle in the development of effective vaccines for many viruses, including PRRSV. However, the contribution of ADE to PRRSV infection remains controversial, especially in vivo. Whether attenuated PRRSV vaccines prevent or worsen subsequent disease in pigs infected by novel PRRSV strains requires more research. In the present study, in vivo experiments were conducted to evaluate ADE under different immune statuses, which were produced by waiting different lengths of time after vaccination with a commercially available attenuated highly pathogenic PRRSV (HP-PRRSV) vaccine (JXA1-R) before challenging the pigs with a novel heterologous NADC30-like strain. RESULTS: Piglets that were vaccinated before being challenged with PRRSV exhibited lower mortality rates, lower body temperatures, higher bodyweight gain, and lower viremia. These results demonstrate that vaccination with JXA1-R alleviated the clinical signs of PRRSV infection in all vaccinated groups. CONCLUSIONS: The obtained data indicate that the attenuated vaccine test here provided partial protection against the NADC30-like strain HNhx. No signs of enhanced PRRSV infection were observed under the applied experimental conditions. Our results provide some insight into the molecular mechanisms underlying vaccine-induced protection or enhancement in PRRSV.

Analysis of ORF5 sequences of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) circulating within swine farms in Costa Rica.

BACKGROUND: Worldwide, Porcine Reproductive and Respiratory Syndrome (PRRS) is among the diseases that cause the highest economic impact in modern pig production. PRRS was first detected in Costa Rica in 1996 and has since then severely affected the local swine industry. Studies of the molecular characterization of circulating strains, correlation with clinical records, and associations with pathogens associated with Porcine Respiratory Disease Complex (PRDC) have not been done in Costa Rica. RESULTS: Sequencing and phylogenetic analysis of ORF5 proved that PRRSV-2 was the only species detected in all locations analyzed. These sequences were grouped into three clusters. When comparing samples from San Jose, Alejuela, and Puntarenas to historical isolates of the previously described lineages (1 to 9), it has been shown that these were closely related to each other and belonged to Lineage 5, along with the samples from Heredia. Intriguingly, samples from Cartago clustered in a separate clade, phylogenetically related to Lineage 1. Epitope analysis conducted on the GP5 sequence of field isolates from Costa Rica revealed seven peptides with at least 80% amino acid sequence identity with previously described and experimentally validated immunogenic regions. Previously described epitopes A, B, and C, were detected in the Santa Barbara-Heredia isolate. CONCLUSIONS: Our data suggest that the virus has three distinct origins or introductions to the country. Future studies will elucidate how recently introduced vaccines will shape the evolutionary change of circulating field strains.

Gene expression in tonsils in swine following infection with porcine reproductive and respiratory syndrome virus.

BACKGROUND: Porcine reproductive and respiratory syndrome (PRRS) is a threat to pig production worldwide. Our objective was to understand mechanisms of persistence of PRRS virus (PRRSV) in tonsil. Transcriptome data from tonsil samples collected at 42 days post infection (dpi) were generated by RNA-seq and NanoString on 51 pigs that were selected to contrast the two PRRSV isolates used, NVSL and KS06, high and low tonsil viral level at 42 dpi, and the favorable and unfavorable genotypes at a genetic marker (WUR) for the putative PRRSV resistance gene GBP5. RESULTS: The number of differentially expressed genes (DEGs) differed markedly between models with and without accounting for cell-type enrichments (CE) in the samples that were predicted from the RNA-seq data. This indicates that differences in cell composition in tissues that consist of multiple cell types, such as tonsil, can have a large impact on observed differences in gene expression. Based on both the NanoString and the RNA-seq data, KS06-infected pigs showed greater activation, or less inhibition, of immune response in tonsils at 42 dpi than NVSL-infected pigs, with and without accounting for CE. This suggests that the NVSL virus may be better than the KS06 virus at evading host immune response and persists in tonsils by weakening, or preventing, host immune responses. Pigs with high viral levels showed larger CE of immune cells than low viral level pigs, potentially to trigger stronger immune responses. Presence of high tonsil virus was associated with a stronger immune response, especially innate immune response through interferon signaling, but these differences were not significant when accounting for CE. Genotype at WUR was associated with different effects on immune response in tonsils of pigs during the persistence stage, depending on viral isolate and tonsil viral level. CONCLUSIONS: Results of this study provide insights into the effects of PRRSV isolate, tonsil viral level, and WUR genotype on host immune response and into potential mechanisms of PRRSV persistence in tonsils that could be targeted to improve strategies to reduce viral rebreaks. Finally, to understand transcriptome responses in tissues that consist of multiple cell types, it is important to consider differences in cell composition.

Fetal cytokine response to porcine reproductive and respiratory syndrome virus-2 infection.

To understand the fetal immune response to porcine reproductive and respiratory virus-2 (PRRSV) and to evaluate the association with fetal viability, pregnant gilts were challenged on gestation day 85 and euthanized 21 days post infection. Based on preservation status and viral load in serum and thymus, fetuses were classified as either uninfected-viable (UNIF), high viral load viable (HV-VIA), or high viral load meconium stained (HV-MEC) and were compared with age matched control (CON) fetuses derived from mock infected gilts. Gene expression of IFNB, IFNG, CCL2, CCL5, CXCL10 and IL10, were all found to be significantly upregulated in the thymus and spleen of both high viral load groups. UNIF fetuses remained largely unaffected, with only small upregulations in IFNA and IL10 in the thymus, and IFNA, CCL5 and CXCL10 in the spleen. Regarding fetal viability, expression of CCL5 was significantly elevated in the thymus and spleen of HV-MEC compared to HV-VIA fetuses. The concentrations of IFNα, IFNγ, TNFα and CCL2 were elevated in the sera of all infected fetuses, whereas IFNß was below the detection limit in all fetal sera. Additional gene expression analysis in the thymus showed significant downregulation of CDK1, CDK2 and CDK4, and upregulation of the inhibitor CDKN1A, suggesting altered regulation of cell cycle progression. Collectively, these results show near complete compartmentalization of the fetal immune response to infected fetuses and suggest this immune response is not a major contributor to fetal death.

Genetic signatures of the immune-escaping type 2 porcine reproductive and respiratory syndrome virus in farms with a robust vaccination program.

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important porcine viruses worldwide. Recently, severe PRRS outbreaks had occurred in two farms located in eastern and southern Thailand where stringent vaccination had been routinely practiced. Genetic analysis of GP5 identified two highly virulent PRRSVs designated as NA/TH/S001/2015 and NA/TH/E001/2016 from the southern and eastern farms, respectively. Both incidences were the first outbreaks of severe PRRSV since the implementation of the modified live virus (MLV) vaccine, indicating the concurrent emergence of immune-escape viruses. The genetics of the two PRRSV variants, the previous studied sequences from Thailand, and the reference strains were characterized with a focus on the GP5 and NSP2 genes. The results indicated that NA/TH/S001/2015 and NA/TH/E001/2016 shared less than 87% nucleotide similarity to the MLV and PRRSV type 2, lineages 1 and 8.7 (NA), respectively. A comparative analysis of the retrospective GP5 sequences categorized the PRRSVs into five groups based on the clinical outcomes, and both of the novel PRRSV strains were in the same group. Epitope A, T cell epitope, and N-linked glycosylation patterns within GP5 of both PRRSV variants were highly variable and significantly differed from those of MLV. As observed in highly virulent type 2 strains, NA/TH/S001/2015 contained a single amino acid deletion at position 33 in the hypervariable region 1 (HV-1) of GP5. Amino acid analysis of the hypervariable region of NSP2 revealed that NA/TH/E001/2016 had a unique deletion pattern that included two discontinuous deletions: a 127-amino acid deletion from residues 301 to 427 and a single amino acid deletion at position 470. These results indicate the emergence of two novel PRRSV strains and highlight the common genetic characteristics of the immune-escaping PRRSV variants.

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.

Porcine reproductive and respiratory syndrome virus: phylogenetic analysis of circulating strains in the Republic of Ireland from 2016 to 2017.

In order to investigate the genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) strains currently circulating in the Republic of Ireland (ROI), the ORF5 gene from 17 field strains originating from four vaccinating commercial herds was sequenced and phylogenetically analysed. High genetic variability was observed between farms at the nucleotide (86.3-95.2%) and amino acid (85.5-96%) levels. Phylogenetic analysis confirmed that all field strains belonged to the European species (type 1) and clustered into three separate groups within the subtype 1 subgroup. This variation may pose challenges for diagnosis and prophylactic control of PRRSV through vaccination in the ROI.

Novel lineage 1 recombinants of porcine reproductive and respiratory syndrome virus isolated from vaccinated herds: genome sequences and cytokine production profiles.

Porcine reproductive and respiratory syndrome virus (PRRSV) is a widely disseminated, macrophage-tropic arterivirus that exhibits profound genetic and pathogenic heterogeneity. The present study was conducted to determine the complete genome sequences of two novel Korean lineage 1 PRRSV-2 strains, KNU-1901 and KNU-1902, which were isolated from vaccinated pig farms experiencing unusually high morbidity and mortality. Both isolates contained notable discontinuous 423-nucleotide deletions (DELs) within the genes encoding nonstructural protein 2 (nsp2) and GP3 when compared with the prototype strain VR-2332. In particular, the nsp2 DEL viruses had unique quadripartite discontinuous DEL signatures (111-1-19-9) in nsp2; this is an expanded version of the tripartite 111-1-19 DEL previously identified in virulent lineage 1 PRRSV-2 strains. Phylogenetic analysis revealed that both novel nsp2 DEL viruses belong to the Korean clade (KOR C) of lineage 1 isolates based on ORF5 but cluster with lineage KOR A strains based on the nsp2 or complete genome sequence. Recombination detection analysis suggested that both novel isolates are recombinants and may have evolved via natural inter-lineage recombination between circulating KOR A and KOR C strains. Interestingly, compared with the prototype VR-2332 virus, the novel nsp2 DEL variants were less efficient at promoting the expression of immune response genes in porcine alveolar macrophage culture. Taken together, we conclude that KNU-1901 and KNU-1902 are recently evolved recombinant variants of the virulent lineage 1 family that caused the regional severe PRRS outbreaks.

Recombination between Vaccine and Field Strains of Porcine Reproductive and Respiratory Syndrome Virus.

We isolated and plaque purified IA76950-WT and IA70388-R, 2 porcine reproductive and respiratory syndrome viruses from pigs in the same herd in Iowa, USA, that exhibited coughing and had interstitial pneumonia. Phylogenetic and molecular evolutionary analysis indicated that IA70388-R is a natural recombinant from Fostera PRRSV vaccine and field strain IA76950-WT.

Prevalence and genetic characteristics of porcine reproductive and respiratory syndrome virus in central China during 2016-2017: NADC30-like PRRSVs are predominant.

NADC30-like strains of porcine reproductive and respiratory syndrome virus (PRRSV) were firstly reported in China in 2013. Since then, these strains have been epidemic in more than 13 provinces/regions. During 2016-2017, a total of 18 PRRSV isolates were obtained from 52 clinical samples in Henan province. Based on comparative and phylogenetic analyses of ORF5 and partial Nsp2 genes, 83.3% (15/18) isolates belonged to NADC30-like strains, and the ORF5 shared 87.4%-95.5% nucleotide identity with NADC30/JL580 and 84.2%-89.9% with JXA1/CH-1a, respectively. The genetic variation analysis showed that extensive amino acid substitutions happened in the significant regions of ORF5 including major linear antigenic epitopes (27-30aa, 37-45aa, 52-61aa) and the potential N-glycosylation sites (32-35aa). 16.7% (3/18) isolates were very close to HP-PRRSV derived attenuated strains. Moreover, these three isolates shared common residues at the positions 33D, 59 N, 164R, 196R in ORF5 and 303D, 399T, 575V, 598R, 604G in Nsp2, which were thought to be unique to modified live vaccines (MLVs) or their derivatives. Therefore, they were probably the revertants from MLVs. Our studies showed that the HP-PRRSV strains seemed to be gradually disappearing and NADC30-like strains had become the main causative agents of PRRS in central China. Comparing with HP-PRRSVs, the ORF5 of NADC30-like PRRSV strains displayed extensive amino acid mutations which may be related with immune evasion. Furthermore, the circulation of MLV derivatives in the fields made the diagnosis and control of PRRSV more complicated.

Characterization of newly emerged NADC30-like strains of porcine reproductive and respiratory syndrome virus in China.

Different strains of porcine reproductive and respiratory syndrome virus (PRRSV) have emerged and circulated in different regions of mainland China since 1996, particularly after 2006. In 2012, NADC30-like PRRSV was first isolated in Henan Province. By 2016, it had spread to most provinces in China. In the present study, the whole genomes (excluding the poly(A) tails) of 13 newly emerged NADC30-like PRRSV strains were sequenced and analyzed. Furthermore, the pathogenicity of SD53-1603, one of the 13 PRRSV strains, was assessed. Phylogenetic analysis showed that these 13 newly emerged NADC30-like PRRSV strains, together with some reference strains, formed a new subgroup (subgroup 5), characterized by a predicted 131-amino-acid deletion in the nonstructural protein (NSP) 2. However, low levels of whole-genome similarity and a wide variety of recombination patterns complicated the classification of the NADC30-like PRRSV isolates. Interestingly, almost all of the recombination breakpoints found in these 13 PRRSV isolates and other NADC30-like PRRSV isolates occurred in genes encoding NSPs and/or minor structural proteins. In addition, piglets infected with the newly emerged NADC30-like strain SD53-1603 displayed clear clinical respiratory symptoms and underwent typical pathological changes. The findings may be useful for elucidating the characteristics and epidemic status of NADC30-like PRRSV in China.

Coding-complete sequence of a vaccine-derived recombinant porcine reproductive and respiratory syndrome virus strain isolated in Hungary.

Porcine reproductive and respiratory syndrome virus 1 is a major cause of swine morbidity and mortality in various parts of the world, including Hungary. A national elimination programme to reduce the associated economic burden was initiated in Hungary in 2012. Using extensive laboratory surveillance, we identified and isolated an unusual PRRSV strain. The complete coding sequence of this isolate was determined and analyzed. The genome of this Hungarian PRRSV1 strain, HUN60077/16, is 15,081 nucleotides in length. Phylogenetic and recombination analysis showed a mosaic structure of the genome where a large fragment of ORF1b and the genomic region coding for ORF3 to ORF7 showed a very close genetic relationship to the vaccine virus Unistrain, while the ORF1a region, the 3' end of ORF1b, and the whole ORF2 were only distantly related to this or any other PRRSV1 strain whose genome sequence is available in the GenBank database. Genomic characterization of PRRSV strains is crucial when possible vaccine-associated cases are identified. This approach not only helps to identify genetic interactions between vaccine and wild-type PRRSV1 strains but may also be needed to prevent trust in commercial vaccines from being undermined.

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.

Genomic sequence and virulence of a novel NADC30-like porcine reproductive and respiratory syndrome virus isolate from the Hebei province of China.

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of porcine reproductive and respiratory syndrome (PRRS), which results in immense economic losses in the swine industry. Outbreaks of disease caused by NADC30-like PRRSV are of great concern in China. Here, a novel variant, NADC30-like PRRSV strain HB17A, was analyzed and its pathogenicity in pigs was examined. The full-length genome sequence of HB17A shared 83.6-95.1% nucleotide similarity with NADC30-like and NADC30 PRRSV without any gene insertions, but with a unique 2-amino acid deletion in Nsp2. A phylogenetic analysis showed that HB17A clustered with NADC30 strains. Different degrees of variation in the signal peptide, transmembrane region (TM), primary neutralizing epitope (PNE), non-neutral epitopes, and N-glycosylation sites were observed in GP5. Challenge experiments showed that HB17A infection resulted in persistent fever, moderate respiratory clinical signs, low levels of viremia and viral loads in serum, and mild gross and microscopic lung lesions. Moreover, IFN-γ, IL-6, and IL-10 cytokine levels were significantly elevated in serum, but the levels of IFN-α and IL-2 were similar to those of the negative controls. HB17A was less pathogenic but was secreted longer in nasal discharge than HP-PRRSV FZ06A. Our findings indicate that HB17A is a novel NADC30-like strain with certain deletions and mutations but with no evidence of genomic recombination. This strain exhibits intermediate virulence in pigs. This research will be help define the evolutionary characteristics of Chinese NADC30-like PRRSV.

Phylogenetic analysis of porcine reproductive and respiratory syndrome virus isolates from Northern Ireland.

To investigate the genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) in Northern Ireland, the ORF5 gene from nine field isolates was sequenced and phylogenetically analysed. The results revealed relatively high diversity amongst isolates, with 87.6-92.2% identity between farms at the nucleotide level and 84.1-93.5% identity at the protein level. Phylogenetic analysis confirmed that all nine isolates belonged to the European (type 1) genotype and formed a cluster within the subtype 1 subgroup. This study provides the first report on PRRSV isolate diversity in Northern Ireland.

Phylogeographic analysis of porcine reproductive and respiratory syndrome virus 1 in Guangdong province, Southern China.

Porcine reproductive and respiratory syndrome virus (PRRSV) is considered an important economic pathogen for the international swine industry. At present, both PRRSV-1 and PRRSV-2 have been confirmed to be co-circulating in China. However, there is little available information about the prevalence or distribution of PRRSV-1 in Guangdong province, southern China. In this study, we performed molecular detection of PRRSV-1 in 750 samples collected from 50 farms in 15 major pig farming regions in this province. After RT-PCR testing, 64% (32/50) of farms were confirmed as PRRSV-1-positive. Surprisingly, PRRSV-1 was circulating on at least one pig farm in all 15 regions; of the 750 samples, 186 samples (24.8%) were positive for PRRSV-1. Furthermore, 15 representative PRRSV-1 ORF5 sequences (606 bp) (n = 1 per region) were obtained from those PRRSV-1-positive regions. Sequence alignment analysis indicated that they shared 81.8% ~ 100% nucleotide and 81.2% ~ 100% amino acid similarity with each other. Although all current PRRSV-1 sequences were divided into pandemic subtype 1, most of them had unique glycoprotein-5 amino acid sequences that are significantly different from other known PRRSV-1 isolates. To conclude, the present findings revealed wide geographical distribution of PRRSV-1 in Guangdong province, southern China. This study further extends the epidemiological significance of PRRSV-1 in China.

Molecular characterization and recombination analysis of porcine reproductive and respiratory syndrome virus emerged in southwestern China during 2012-2016.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important swine pathogen causing tremendous economic losses to the swine industry. To investigate the prevalence of PRRSV of genotype 2 (North American type, NA-type) in southwestern China, the Nsp2 hypervariable region (Nsp2 HV) and ORF5 of 61 PRRS viruses collected during 2012-2016 were sequenced and analyzed. All the virus detected clustered into the JXA1-like (52/61), VR-2332-like (7/61), and NADC30-like (2/61) sub-genotypes. Five deletions in Nsp2 HV were detected in addition to the typical 30aa discontinuous deletion in HP-PRRSV, and two of these five were not reported previously. Strikingly, two PRRS virus (SCnj16 and SCcd16) isolated in 2016 contained the classic HP-PRRSV molecular marker in the Nsp2-coding region, but belonged to the NADC30-like sub-genotype on the ORF5 gene. Further recombination and phylogenetic analysis on the two complete genomic sequences revealed that they may have originated from recombination events between the NADC30 and Chinese HP-PRRSV strains. The present study suggests that the endemic PRRSVs in the region have continuously evolved and new vaccine strategies are necessary for more efficient control of the virus.

Geographic distribution and molecular analysis of porcine reproductive and respiratory syndrome viruses circulating in swine farms in the Republic of Korea between 2013 and 2016.

BACKGROUND: Porcine reproductive and respiratory syndrome virus (PRRSV) causes devastating disease characterized by reproductive failure and respiratory problems in the swine industry. To understand the recent prevalence and genetic diversity of field PRRSVs in the Republic of Korea, open reading frames (ORFs) 5 and 7 of PRRSV field isolates from 631 PRRS-affected swine farms nationwide in 2013-2016 were analyzed along with 200 Korean field viruses isolated in 2003-2010, and 113 foreign field and vaccine strains. RESULTS: Korean swine farms were widely infected with PRRSVs of a single type (38.4 and 37.4% for Type 1 and Type 2 PRRSV, respectively) or both types (24.2%) with up to approximately 83% nucleotide sequence similarity to prototype PRRSVs (Lelystad or VR2332). Phylogenetic analysis based on the ORF5 nucleotide sequence revealed that Korean Type 1 field isolates were classified as subgroups A, B, and C under subtype 1, while Korean Type 2 field isolates were classified as lineages 1 and 5 as well as three Korean lineages (kor A, B, and C) with the highest infection prevalence in subgroup A (50.5%) and lineage 5 (15.3%) for Type 1 and Type 2 PRRSV, respectively, among ORF5-positive farms. In particular, the lineages kor B and C were identified as novel lineages in this study, and lineage kor B comprised only the field viruses isolated from Gyeongnam Province in 2014-2015, establishing regionally unique genetic characteristics. It has also recently been confirmed that commercialized vaccine-like viruses (subgroup C) of Type 1 PRRSV and NADC30-like viruses of Type 2 PRRSV (lineage 1) are spreading rapidly in Korean swine farms. The Korean field viruses were also expected to be antigenically variable as shown in the high diversity of neutralizing epitopes and N-glycosylation sites. CONCLUSIONS: This up-to-date information regarding recent field PRRSVs should be taken into consideration when creating strategies for the application of PRRS control measures, including vaccination in the field.

Label-Free Quantitative Proteomic Analysis of Differentially Expressed Membrane Proteins of Pulmonary Alveolar Macrophages Infected with Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus and Its Attenuated Strain.

Significant differences exist between the highly pathogenic (HP) porcine reproductive and respiratory syndrome virus (PRRSV) and its attenuated pathogenic (AP) strain in the ability to infect host cells. The mechanisms by which different virulent strains invade host cells remain relatively unknown. In this study, pulmonary alveolar macrophages (PAMs) are infected with HP-PRRSV (HuN4) and AP-PRRSV (HuN4-F112) for 24 h, then harvested and subjected to label-free quantitative MS. A total of 2849 proteins are identified, including 95 that are differentially expressed. Among them, 26 proteins are located on the membrane. The most differentially expressed proteins are involved in response to stimulus, metabolic process, and immune system process, which mainly have the function of binding and catalytic activity. Cluster of differentiation CD163, vimentin (VIM), and nmII as well as detected proteins are assessed together by string analysis, which elucidated a potentially different infection mechanism. According to the function annotations, PRRSV with different virulence may mainly differ in immunology, inflammation, immune evasion as well as cell apoptosis. This is the first attempt to explore the differential characteristics between HP-PRRSV and its attenuated PRRSV infected PAMs focusing on membrane proteins which will be of great help to further understand the different infective mechanisms of HP-PRRSV and AP-PRRSV.