Epidemiological investigation and genetic evolutionary analysis of PRRSV-1 on a pig farm in China

A lineage 1 branch porcine reproductive and respiratory syndrome virus live vaccine candidate provides broad cross-protection against HP-like PRRSV in piglets

Multiple porcine reproductive and respiratory syndrome virus (PRRSV) subtypes coinfect numerous pig farms in China, and commercial PRRSV vaccines offer limited cross-protection against heterologous strains. Our previous research confirmed that a PRRSV lineage 1 branch attenuated live vaccine (SD-R) provides cross-protection against HP-PRRSV, NADC30-like PRRSV and NADC34-like PRRSV. HP-PRRSV has undergone significant genetic variation following nearly two decades of evolution and has transformed into a subtype referred to as HP-like PRRSV, which also exhibits high pathogenicity. The effectiveness of immunising piglets with the SD-R strain to provide protection against infection with HP-like PRRSV remains uncertain. In the present study, we evaluated the protective effects of SD-R vaccine strains on DLF-challenged piglets. The results revealed that piglets challenged with DLF presented clinical symptoms such as continuous high fever and an obvious decrease in daily weight gain. Importantly, the piglets immunised with SD-R exhibited notable reductions in pathological damage, especially of decreases in DLF-induced thymic atrophy. Moreover, the serum of SD-R-immunised piglets strongly neutralised DLF, and the number of SD-R-vaccinated piglets demonstrating viraemia was greatly reduced. These results suggest that the PRRSV lineage 1 branch live vaccine candidate provides broad cross-protection against HP-like PRRSV in piglets.

Genetic variation in NSP4 of type 1 porcine reproductive and respiratory syndrome virus in China

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by a high mutation rate. Although research has largely focused on PRRSV-2, the detection rate of PRRSV-1 in China is increasing. To investigate the prevalence and genetic variation of NSP4, a key gene in the regulation of host immunity, in PRRSV-1 in China, publicly available whole-genome sequence data and NSP4 sequences were obtained for analyses of nucleotide and amino acid homology, substitutions, and phylogenetic relationships.

RESULTS

The nucleotide homology of NSP4 between 32 PRRSV-1 and 8 PRRSV-2 strains ranged from 57.3 to 62.4%, and the amino acid homology ranged from 58.6 to 64.5%. Among the 32 PRRSV-1 strains, the nucleotide homology of NSP4 ranged from 75.4 to 100.0% and the amino acid homology ranged from 81.3 to 100.0%. Comparisons of NSP4 amino acid sequences of 32 PRRSV-1 and 8 PRRSV-2 strains revealed a deletion at the 83rd amino acid residue in PRRSV-1 and mutations at various amino acid residues. A phylogenetic analysis showed that the PRRSV-1 strains isolated in China clustered into four subgroups of Subtype I Global: Amervac-like, BJEU06-1-like, HKEU16-like, and NMEU09-1-like strains.

CONCLUSION

PRRSV-1 NSP4 exhibits similarities to Subtype I Global strains and clusters into four subgroups. Although it differs from PRRSV-2 NSP4 with a deletion in the 83rd amino acid residue, the amino acid residues of the catalytic triad are conserved. These findings have important implications for the development of secure and reliable detection methods as well as new drugs and vaccines and are expected to guide further research on PRRSV-1.

Recombination and Genetic Diversity Analysis of Porcine Reproductive and Respiratory Syndrome 1 Nonstructural Protein 2 Genes in China

BACKGROUND

Porcine reproductive and respiratory syndrome (PRRS) has been present in China for about 30 years, and because of the high mutability of PRRSV, it causes huge economic losses to pig enterprises every year. PRRSV-2 is widely prevalent in China, and the detection rate of PRRSV-1 is also on the rise. Nonstructural protein 2 (NSP2) is a highly variable protein with multiple biological functions, such as PRRSV replication, which plays an important role in understanding PRRSV variation and epidemic alerts.

OBJECTIVES

The epidemic characteristics and recombination of PRRSV-1 NSP2 are still unknown. The purpose of this study is to study the epidemic characteristics of PRRSV-1 NSP2 and lay a foundation for the prevention and control of PRRSV-1.

METHODS

In this study, we collected several PRRSV-1 and PRRSV-2 NSP2 gene sequences for gene sequence and recombination analyses, aiming to analyze the recombination pattern and genetic variation in the PRRSV-1 NSP2 genes in China.

RESULTS

The genetic similarity results showed that the 69 PRRSV-1 NSP2 gene sequences collected in this study showed nucleotide similarity ranging from 67.3% to 100.0% and amino acid similarity ranging from 64.3% to 100.0%. Amino acid sequence comparison showed that PRRSV-1 had more amino acid deletion or substitution sites than PRRSV-2. NSP2 also contains special amino acid regions such as the highly immunogenic region. PRRSV-1 can be categorized into four strains, NMEU09-1-like, BJEU06-1-like, HKEU-16-like and Amervac-like isolates, and are at different positions in the ML and NJ phylogenetic trees. In the ninety selected PRRSVs, six recombination events were detected using recombination analysis, two of which occurred in Chinese PRRSV-1 strains. Therefore, sequence analysis of NSP2 helps us to understand the prevalence and variation in PRRSV-1 in China over the past two decades and provides a theoretical basis for studying the epidemiology and evolution of NSP2.

Reproductive Failure in Smallholder Pig Farms in East and Southeast Asia: A Systematic Review

Reproductive failure has significant socioeconomic impacts on smallholder pig farms. This systematic review was conducted to compile the types of reproductive failures and their underlying causes reported in smallholder pig farms from East and Southeast Asia and to identify relevant knowledge gaps. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 26 peer-reviewed studies met the eligibility criteria and were included in our synthesis. These studies were conducted in 11 countries, with Vietnam, China, and Thailand representing the highest share (53.8%). Only six studies (23%) investigated reproductive failure as their primary objective. Stillbirth, mummification, late-term abortion, and weak-born piglets were the predominant reproductive failures reported from smallholder pig farms across the region. The most frequently cited viral pathogens associated with these failures were porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV-2). Common non-infectious risk factors included extreme climate conditions (e.g., heat stress), poor diet and housing, and suboptimal boar management. Our synthesis highlighted a dearth of research focused on reproductive failure in smallholder pig farms in the region and emphasised the need for more targeted studies to clarify the biological, environmental, and managerial risk factors contributing to reproductive failure. This will facilitate the development of targeted prevention and control measures that account for the unique farming conditions and challenges smallholder farms face in East and Southeast Asia.

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

Introduction

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

Methods

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

Results

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

Discussion

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

Isolation and Genomic Characterization of a Novel Porcine Reproductive and Respiratory Syndrome Virus 1 from Severely Diseased Piglets in China in 2024

Since the first isolation of the porcine reproductive and respiratory syndrome virus 1 (PRRSV-1) BJEU06-1 strain from a Beijing pig farm in 2006, more and more PRRSV-1 isolates have been identified in China. In this study, we performed the routine detection of PRRSV-1 using 1521 clinical samples collected in 12 provinces/cities from February 2022 to May 2024. Only three lung samples from severely diseased piglets collected in January 2024 were detected as PRRSV-1-positive (0.197%, 3/1521). A PRRSV-1 strain (AHEU2024-2671) was successfully isolated in primary alveolar macrophages (PAMs) but not in Marc-145 cells. Genome sequencing showed that the AHEU2024-2671 isolate shared the highest genome similarity (90.67%) with the SC2020-1 isolate but only 84.01% similarity with the predominant BJEU06-1 strain. Noticeably, the AHEU2024-2671-like isolates not only contained deletions in nsp2 and the GP3-GP4 overlap region, but also contained a unique 6 nt deletion between nsp12 and the ORF2 gene. Furthermore, a genome-based phylogenetic tree supported that the AHEU2024-2671-like isolates form a novel subgroup within subtype 1. Overall, this study not only supported the idea that PRRSV-1 is rapidly evolving in Chinese swine herds, but also pulled the alarm that novel PRRSV-1 isolates with potentially increased pathogenicity might already exist in China, although they are still rarely detected among Chinese pigs.

Whole Genome Characterization and Pathogenicity of a SC2020-1-Like PRRSV-1 Strain Emerging in Southwest China

Porcine reproductive and respiratory syndrome virus (PRRSV), encompassing PRRSV-1 and PRRSV-2, significantly impacts the global pig industry by causing reproductive disorders and respiratory difficulties. In this paper, we isolated a novel PRRSV-1 strain, named SCPJ2023, from weaned piglets in Sichuan. Utilizing primary macrophages, we isolated SCPJ2023 and performed complete genome sequencing through metagenomic analysis. Phylogenetic analysis classified SCPJ2023 as pan-European subtype 1. SCPJ2023 showed a 95.3% similarity to SC2020-1. Amino acid analysis identified differences in Nsp2, GP3, and GP4 between SCPJ2023 and other representative strains. In vivo challenge experiments demonstrated that SCPJ2023 induced clinical symptoms in piglets, including coughing, fever, reduced appetite, and depression. Pathological examinations revealed hemorrhage and congestion, increased inflammatory cells, thickening of the alveolar wall, and collapse of the alveolar cavity in SCPJ2023-infected piglets. Altogether, our study identified a novel pathogenic isolate of PRRSV-1, expanding the newly named SC2020-1-like subgroup by identifying additional strains beyond the initial SC2020-1 isolate.

A chimeric strain of porcine reproductive and respiratory syndrome virus 2 derived from HP-PRRSV and NADC30-like PRRSV confers cross-protection against both strains

Porcine reproductive and respiratory syndrome (PRRS) is one of the most significant swine viral infectious diseases worldwide. Vaccination is a key strategy for the control and prevention of PRRS. At present, the NADC30-like PRRSV strain has become the predominant epidemic strain in China, superseding the HP-PRRSV strain. The existing commercial vaccines offer substantial protection against HP-PRRSV, but their efficacy against NADC30-like PRRSV is limited. The development of a novel vaccine that can provide valuable cross-protection against both NADC30-like PRRSV and HP-PRRSV is highly important. In this study, an infectious clone of a commercial MLV vaccine strain, GD (HP-PRRSV), was first generated (named rGD). A recombinant chimeric PRRSV strain, rGD-SX-5U2, was subsequently constructed by using rGD as a backbone and embedding several dominant immune genes, including the NSP2, ORF5, ORF6, and ORF7 genes, from an NADC30-like PRRSV isolate. In vitro experiments demonstrated that chimeric PRRSV rGD-SX-5U2 exhibited high tropism for MARC-145 cells, which is of paramount importance in the production of PRRSV vaccines. Moreover, subsequent in vivo inoculation and challenge experiments demonstrated that rGD-SX-5U2 confers cross-protection against both HP-PRRSV and NADC30-like PRRSV, including an improvement in ADG levels and a reduction in viremia and lung tissue lesions. In conclusion, our research demonstrated that the chimeric PRRSV strain rGD-SX-5U2 is a novel approach that can provide broad-spectrum protection against both HP-PRRSV and NADC30-like PRRSV. This may be a significant improvement over previous MLV vaccinations.

Sequence analysis of the GP5 protein of porcine reproductive and respiratory syndrome virus in Vietnam from 2007 to 2023

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent 13 of porcine reproductive and respiratory syndrome (PRRS), which is one of the most economically 14 devastating viruses in the Vietnamese swine industry.

Methods

With a view toward determining the 15 genetic variation among PRRSV strains in Vietnam, we examined 271 PRRSV GP5 protein 16 sequences obtained from strains isolated in Vietnam from 2007 to 2023, for which we constructed 17 phylogenetic trees. Additionally, a collection of 52 PRRSV-1 strains and 80 PRRSV-2 strains 18 isolated in different years were specifically selected for nucleotide and amino acid homology analysis 19 and amino acid sequence alignment.

Results

The results revealed 76.1%-100.0% nucleotide and 20 75.2%-100.0% amino acid homologies for the PRRSV-1 GP5 gene, and 81.8%-100.0% nucleotide 21 and 81.1%-100.0% amino acid homologies for the PRRSV-2 GP5 gene. Amino acid mutation sites 22 in PRRSV-2 were found to be primarily distributed in the signal peptide region, antigenic sites, two 23 T-cell antigen regions, two highly variable regions (HVRs), and in the vicinity of the neutralizing 24 epitope, with a deletion mutation occurring in the neutralizing epitope, whereas amino acid mutations 25 in the PRRSV-1 sequences were found to occur predominantly in two T-cell epitopes. Genetic 26 analysis revealed that PRRSV-1 strains in Vietnam are of subtype 1 (Global), whereas PRRSV-2 27 strains are categorized into sublineages L1A, L5A, and L8E, with L8E being the predominantly 28 prevalent strain at present. Recombination analyses indicated that no significant recombination 29 events have occurred in any of the assessed 271 Vietnamese PRRSV strains.

Discussion

Our 30 analyses of 271 Vietnamese PRRSV strains have yielded valuable insights regarding the 31 epidemiological trends and genetic dynamics of PRRSV in Vietnam, and will provide a theoretical 32 basis for formulating prevention and control measures for PRRS and the development of PRRS 33 vaccines.

Investigation of the distribution and origin of porcine reproductive and respiratory syndrome virus 1 in the swine production chain: A retrospective study of three farms in Thailand

Background and Aim

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV), is a global issue that affects Thai swine as well. In Thailand, PRRSV-2 predominates over PRRSV-1. The origin of PRRSV-1 transmission remains undiscovered. This study traced the source of infected pigs responsible for disease transmission among three pig-fattening farms and analyzed the spread of PRRSV-1.

Materials and Methods

A total of 696 swine samples from breeding and pig-fattening farms in Thailand were screened for PRRSV using open reading frames (ORF7) reverse transcription polymerase chain reaction (RT-PCR). Positive samples were identified as PRRSV-1 using ORF5 RT-PCR. The analysis included the study of nucleotide homology, GP5 amino acid sequences, and N-linked glycosylation patterns to assess the spread of PRRSV-1 across these farms.

Results

Genetic examination identified 28 PRRSV-1-positive samples, of which 13 were chosen as representatives. These strains were categorized into three groups based on breeding farm pig houses and showed distinct distribution patterns across pig-fattening farms. Group 1 included piglets transferred from pig house A to Nakhon Pathom, Chonburi, and Sa Kaeo. Groups 2 and 3 showed transfers from pig houses F and H to Chonburi and Sa Kaeo farms. All 13 PRRSV-1 strains were categorized into PRRSV-1 subtype 1/clade H. N-linked glycosylation analysis revealed that nearly all PRRSV-1 strains exhibited a conserved glycosylation pattern at amino acid positions N37, N46, and N53. This pattern is consistent with the glycosylation profile of the previous Thai PRRSV-1 subtype 1/clade H.

Conclusion

The present study highlights the persistent presence of PRRSV-1 in Thai swine, which leads to sporadic outbreaks. The molecular genetic analysis identified three primary strain groups dispersed throughout the pig production system, emphasizing the importance of regular monitoring for new PRRSV strains in this herd. Understanding the PRRSV-1 distribution in swine farms is vital for veterinarians. This knowledge supports strategies for eradicating the virus and managing swine health effectively in Thailand.

Dissecting Genetic Diversity and Evolutionary Trends of Chinese PRRSV-1 Based on Whole-Genome Analysis

Porcine reproductive and respiratory syndrome (PRRS) poses a serious threat to the Chinese swine industry. The etiological agent PRRSV can be classified as either PRRSV-1 or PRRSV-2. Recent studies have revealed an increase in the rates of PRRSV-1 detection and a wider PRRSV-1 distribution. However, the PRRSV-1 genome in China has yet to be fully characterized. In this study, 24 whole PRRSV-1 genomes from different swine farms were assembled and subjected to whole-genome analysis. A phylogenetic analysis based on the complete genome and ORF5 sequences revealed that the PRRSV-1 strains from China belonged to Western European Subtype I and could be classified into seven subgroups. Statistical analysis revealed that BJEU06-1-Like PRRSV is currently the predominant PRRSV-1 strain. Moreover, a similarity analysis showed low pairwise similarity between most PRRSV-1 genomes from different pig farms. Amino acid alignments of the Nsp2 gene revealed that the BJEU06-1-Like subgroup had five discontinued aa deletions (4 + 1). The new subgroup 1 had 11 continued aa deletions and an aa insertion, the new subgroup 2 had two discontinued aa deletions (1 + 1), and, except for in the case of HKEU16, the HKEU16-Like subgroup had five discontinuous aa deletions (1 + 4). Recombination analysis revealed that the BJEU06-1-Like and NMEU09-1-Like strains participated extensively in recent recombination events. The analysis of positive selection suggested that there were 15 positively selected codons in site model, and there were five sites under positive selection in the BJEU06-1-Like subgroup in the branch-site model. The mean rate and tMRCA for PRRSV-1 strains from China were 4.11 × 10-3 substitutions/site/year and 1,969.63, respectively. Thus, it is crucial to strengthen epidemiological surveys of PRRSV-1 in China, especially those monitoring BJEU06-1-Like PRRSV.

Development and application of a blocking ELISA based on a N protein monoclonal antibody for the antibody detection against porcine reproductive and respiratory syndrome virus 2

Porcine reproductive and respiratory syndrome (PRRS) is one of the most widespread illnesses in the world's swine business. To detect the antibodies against PRRSV-2, a blocking enzyme-linked immunosorbent assay (B-ELISA) was developed, utilizing a PRRSV-2 N protein monoclonal antibody as the detection antibody. A checkerboard titration test was used to determine the optimal detection antibody dilution, tested pig serum dilution and purified PRRSV coated antigen concentration. After analyzing 174 negative pig sera and 451 positive pig sera, a cutoff value of 40 % was selected to distinguish between positive and negative sera using receiver operating characteristic curve analysis. The specificity and sensitivity of the assay were evaluated to equal 99.8 % and 96 %, respectively. The method had no cross-reaction with PCV2, PRV, PPV, CSFV, PEDV, TGEV, and PRRSV-1 serum antibodies, and the coefficients of variation of intra-batch and inter-batch repeatability experiments were both <10 %. A total of 215 clinical serum samples were tested, and the relative coincidence rate with commercial ELISA kit was 99.06 %, and the kappa value was 0.989, indicating that these two detection results exhibited high consistency. Overall, the B-ELISA should serve as an ideal method for large-scale serological investigation of PRRSV-2 antibodies in domestic pigs.

Characterization and Pathogenicity of the Novel Porcine Reproductive and Respiratory Syndrome Virus 1 Strain SL-01 in China

Currently, PRRSV-1 causes a large number of clinical infections in Chinese swine herds, and the prevalence of new strains has presented great challenges. In this study, the novel PRRSV-1 strain SL-01 was isolated, with a genome length of 14,978 bp, and genetic evolution analysis revealed that it belonged to a new subtype branch. Sequence homology analysis showed that the strain was only 82.2%-86.7% identical to the current classical PRRSV-1 strains. In particular, the novel strain exhibited a unique deletion pattern in Nsp2. In addition, GP3 and GP4 of the SL-01 strain showed four consecutive amino acid deletions in the highly variable regions at amino acids 243-248 and 63-68, respectively. Further challenges in piglet and pregnant sow demonstrated that the SL-01 strain could cause the piglet fever and death but less pathogenic to pregnant sow. Overall, the characterization and pathogenicity of a novel PRRSV-1 strain were first explored and provide a prevention for pig farms.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Research Progress on Porcine Reproductive and Respiratory Syndrome Virus NSP7 Protein

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious and severe infectious disease caused by the PRRS virus (PRRSV). PRRS is characterized by reproductive disorders in sows and respiratory dysfunction in pigs. Non-structural protein 7 (NSP7) is one of the most conserved functional proteins in PRRSV, and it plays an important role in viral replication and humoral immune responses in infected hosts. This review discusses the biological characteristics of NSP7 to provide theoretical support for its application in PRRS diagnosis, novel vaccine design, and therapeutic drug development.

Recent Progress in Studies of Porcine Reproductive and Respiratory Syndrome Virus 1 in China

Due to the high incidence of PRRSV mutation and recombination, PRRSV infection is difficult to prevent and control in China and worldwide. Two species of PRRSV, Betaarterivirus suid 1 (PRRSV-1) and Betaarterivirus suid 2 (PRRSV-2), exist in China, and PRRSV-1 has always received less attention in China. However, the number of PRRSV-1 strains detected in China has increased recently. To date, PRRSV-1 has spread to more than 23 regions in China. Based on the phylogenetic analysis of ORF5 and the whole genome of PRRSV-1, Chinese PRRSV-1 can be divided into at least seven independent subgroups. Among them, BJEU06-1-like has become the mainstream subgroup in some regions of China. This subgroup of strains has a 5-aa (4 + 1) characteristic discontinuous deletion pattern at aa 357~aa 360 and aa 411 in Nsp2. Previous studies have indicated that the pathogenicity of PRRSV-1 in China is mild, but recent studies found that the pathogenicity of PRRSV-1 was enhanced in China. Therefore, the emergence of PRRSV-1 deserves attention, and the prevention and control of PRRSV-1 infection in China should be strengthened. PRRSV infection is usually prevented and controlled by a combination of virus monitoring, biosafety restrictions, herd management measures and vaccination. However, the use of PRRSV-1 vaccines is currently banned in China. Thus, we should strengthen the monitoring of PRRSV-1 and the biosafety management of pig herds in China. In this review, we summarize the prevalence of PRRSV-1 in China and clarify the genomic characteristics, pathogenicity, vaccine status, and prevention and control management system of PRRSV-1 in China. Consequently, the purpose of this review is to provide a basis for further development of prevention and control measures for PRRSV-1.

Progress in PRRSV Infection and Adaptive Immune Response Mechanisms

Since its discovery, Porcine reproductive and respiratory syndrome (PRRS) has had a huge impact on the farming industry. The virus that causes PRRS is Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and because of its genetic diversity and the complexity of the immune response, the eradication of PRRS has been a challenge. To provide scientific references for PRRSV control and vaccine development, this study describes the processes of PRRSV-induced infection and escape, as well as the host adaptive immune response to PRRSV. It also discusses the relationship between PRRSV and the adaptive immune response.

Genomic characteristics of a novel emerging PRRSV branch in sublineage 8.7 in China

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused serious economic losses to the pig industry worldwide. During the continuous monitoring of PRRSV, a new PRRSV strain type with novel characteristics was first identified in three different regions of Shandong Province. These strains presented a novel deletion pattern (1 + 8 + 1) in the NSP2 region and belonged to a new branch in sublineage 8.7 based on the ORF5 gene phylogenetic tree. To further study the genomic characteristics of the new-branch PRRSV, we selected a sample from each of the three farms for whole-genome sequencing and sequence analysis. Based on the phylogenetic analysis of the whole genome, these strains formed a new independent branch in sublineage 8.7, which showed a close relationship with HP-PRRSV and intermediate PRRSV according to nucleotide and amino acid homology but displayed a completely different deletion pattern in NSP2. Recombinant analysis showed that these strains presented similar recombination patterns, all of which involved recombination with QYYZ in the ORF3 region. Furthermore, we found that the new-branch PRRSV retained highly consistent nucleotides at positions 117-120 (AGTA) of a quite conserved motif in the 3'-UTR; showed similar deletion patterns in the 5'-UTR, 3'-UTR and NSP2; retained characteristics consistent with intermediate PRRSV and exhibited a gradual evolution trend. The above results showed that the new-branch PRRSV strains may have the same origin and be similar to HP-PPRSV also evolved from intermediate PRRSV, but are distinct strains that evolved simultaneously with HP-PRRSV. They persist in some parts of China through rapid evolution, recombine with other strains and have the potential to become epidemic strains. The monitoring and biological characteristics of these strains should be further studied.

Metagenomic and Pathogenic Assessments Identify a Pathogenic Porcine Reproductive and Respiratory Syndrome Virus 1 with New Deletions from Adult Slaughter Pig in 2022

Since we first reported porcine reproductive and respiratory syndrome virus 1 (PRRSV1) wild type strains in mainland China in 2011, PRRSV1 infection has been detected in more than 20 provinces in China. During the routine investigation of PRRSV1 epidemiology in 2022, we isolated a novel PRRSV1 strain (SD1291) from an adult slaughter pig in Linyi, Shandong Province. The SD1291 could only be isolated with primary alveolar macrophages (PAMs), not with Marc-145 cells. In addition, the 2022 SD1291 isolate has higher in vitro replication efficacy than the 2014 PRRSV1 HLJB1 isolate in PAMs. Due to high genetic variation, the complete genome of SD1291 was determined by metagenomic sequencing, which showed that SD1291 shares the highest genome similarity (88.12%) with the PRRSV1 HeB47 isolate. Sequence alignment results identified a four-amino-acid deletion in nsp2 and a five-amino-acid deletion in the GP3 and GP4 overlap region of SD1291. A complete-genome-based phylogenetic tree showed that SD1291 is grouped with BJEU06-1-like PRRSV1 isolates. A piglets' challenge study showed that SD1291 can cause high fever (the highest is 41°C), reduced weight gain, mild lung consolidation, and interstitial pneumonia indicating that SD1291 is a pathogenic PRRSV1 isolate. Overall, this study first identified a novel pathogenic PRRSV1 isolate from an adult slaughter pig in China. Our findings also suggested that new PRRSV1 variants could escape the current PRRSV vaccination system and circulate in adult swine herds, which deserve more attention.

Genomic Characterization and Pathogenicity of BJEU06-1-Like PRRSV-1 ZD-1 Isolated in China

Porcine reproductive and respiratory syndrome virus (PRRSV)-1 and PRRSV-2 have long been cocirculating in China. To date, all PRRSV-1 strains in China have been classified as subtype 1. We investigated the prevalence of PRRSV-1 in several areas of China from 2016 to 2022 and found that BJEU06-1-like strains comprised the main epidemic branch of PRRSV-1. Pathogenicity data for this subgroup are currently lacking. In this study, the Chinese BJEU06-1-like PRRSV-1 strain ZD-1 was isolated from primary alveolar macrophages (PAMs). ZD-1 has undergone no recombination and has a 5-aa discontinuous deletion in the Nsp2 protein, similar to other BJEU06-1-like strains; additionally, ZD-1 has a 26 aa C-terminal truncation in the GP3 gene. Pathogenicity studies revealed that ZD-1 causes obvious clinical symptoms: prolonged fever; reduced body weight; alveolar epithelial proliferation and moderate alveolar diaphragm widening in the lungs; diffuse lymphocytic hyperplasia in the lymph nodes; high levels of viremia in the serum; and elevated viral loads in the lungs, lymph nodes, and tonsils. These results suggested that the BJEU06-1-like PRRSV-1 strain ZD-1 is moderately pathogenic to piglets. This is the first study to evaluate the pathogenicity of the BJEU06-1-like branch in China, enriching the understanding of PRRSV-1 in China.