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.

Classical swine fever (CSF) is one of the most devastating and highly contagious viral diseases in the world. Since late 2014, outbreaks of a new sub-genotype 2.1d CSF virus (CSFV) had caused substantial economic losses in numbers of C-strain vaccinated swine farms in China. The objective of the present study was to explore the genomic characteristics and pathogenicity of the newly emerged CSFV isolates in China during 2014–2015. All the new 8 CSFV isolates belonged to genetic sub-genotype 2.1d. Some genomic variations or deletions were found in the UTRs and E2 of these new isolates. In addition, the pathogenicity of HLJ1 was less than Shimen, suggesting the HLJ1 of sub-genotype 2.1d may be a moderated pathogenic isolate and the C-strain vaccine can supply complete protection. The new CSFV isolates with unique genomic characteristics and moderate pathogenicity can be epidemic in many large-scale C-strain vaccinated swine farms. This study provides the information should be merited special attention on establishing prevention and control policies for CSF.

The newly emerged sublineage 1.5 (NADC34-like) porcine reproductive and respiratory syndrome virus (PRRSV) has posed a direct threat to the Chinese pig industry since 2018. However, the prevalence and impact of NADC34-like PRRSV on Chinese pig farms is unclear. In the present study, we continuously monitored pathogens—including PRRSV, African swine fever virus (ASFV), classical swine fever virus (CSFV), pseudorabies virus (PRV), and porcine circovirus 2 (PCV2)—on a fattening pig farm with strict biosecurity practices located in Heilongjiang Province, China, from 2020 to 2021. The results showed that multiple types of PRRSV coexisted on a single pig farm. NADC30-like and NADC34-like PRRSVs were the predominant strains on this pig farm. Importantly, NADC34-like PRRSV—detected during the period of peak mortality—was one of the predominant strains on this pig farm. Sequence alignment suggested that these strains shared the same 100 aa deletion in the NSP2 protein as IA/2014/NADC34 isolated from the United States (U.S.) in 2014. Phylogenetic analysis based on open reading frame 5 (ORF5) showed that the genetic diversity of NADC34-like PRRSV on this farm was relatively singular, but it had a relatively high rate of evolution. Restriction fragment length polymorphism (RFLP) pattern analysis showed that almost all ORF5 RFLPs were 1-7-4, with one 1-4-4. In addition, two complete genomes of NADC34-like PRRSVs were sequenced. Recombination analysis and sequence alignment demonstrated that both viruses, with 98.9% nucleotide similarity, were non-recombinant viruses. This study reports the prevalence and characteristics of NADC34-like PRRSVs on a large-scale breeding farm in northern China for the first time. These results will help to reveal the impact of NADC34-like PRRSVs on Chinese pig farms, and provide a reference for the detection and further prevention and control of NADC34-like PRRSVs.

Background: NADC30-like PRRSV was first identified in China in 2012 and had become the predominant circulating strain since 2016. Currently, the recombination patterns of NADC30-like PRRSV in China exhibit a high degree of complexity, characterized by low whole-genome sequence homology. The genomic features and epidemiological trends of these strains remain to be elucidated. Results: To evaluate the prevalence of NADC30-like PRRSV in China, this study acquired 30 whole-genome sequences of NADC30-like strains via Next-Generation Sequencing (NGS). These sequences were subsequently integrated with 224 whole-genome sequences from China available in the GenBank database. A comprehensive analysis of the genomic characteristics of contemporary NADC30-like PRRSV strains in China was conducted. Recombinant analysis indicated a yearly increase in the number of NADC30-like strains exhibiting recombination signals, whereas nonrecombinant NADC30-like strains have become nearly extinct. Among the recombination events, those involving L1C and L8E as parental strains are most prevalent. Based on the results of recombination and phylogenetic analyses, this study classified 120 Chinese NADC30-like strains with similar recombination characteristics into groups NADC30-R1 to R12. The intra-group genetic distances of the NADC30-R1 to R12 groups approximately 5.73% (SD ± 1.68), while the inter-group genetic distances between different groups are usually stably greater than 10%. The amino acid alignment of Nsp2 demonstrated that all NADC30-R1 to R12 strains exhibit a discontinuous deletion of 131 amino acids. These classifications do not exhibit consistent pathogenic characteristics within groups, with most NADC30-like PRRSVs showing moderate virulence. Geographical distribution analysis indicated that NADC30 whole-genome sequences in China originated from 19 provinces. Notably, the NADC30-R1 and NADC30-R2 strains are the most widely distributed and abundant, suggesting that these variants have established localized epidemics in specific regions. Conclusion: In summary, the vast majority of NADC30-like strains in our country have undergone recombination, L1C + L8E is the most common recombination mode. The NADC30-like strains in China can be classified into 12 different recombination patterns, NADC30-R1 and NADC30-R2 strains are already showing pandemic trends. These findings provide a critical foundation for future NADC30-like PRRSV prevention and control strategies.

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.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that endangers the swine industry worldwide. Recently, lineage 1 PRRSVs, especially NADC30-like PRRSVs, have become the major endemic strains in many pig-breeding countries. Since 2016, NADC30-like PRRSV has become the predominant strain in China. Unfortunately, current commercial vaccines cannot provide sufficient protection against this strain. Here, an attenuated lineage 1 PRRSV strain, named SD-R, was obtained by passaging an NADC30-like PRRSV strain SD in Marc-145 cells for 125 passages. Four-week-old PRRSV-free piglets were vaccinated intramuscularly with 10^5.0TCID₅₀ SD-R and then challenged intramuscularly (2 mL) and intranasally (2 mL) with homologous NADC30-like PRRSV SD (1 × 10^5.0TCID₅₀/_mL) and heterologous NADC30-like PRRSV HLJWK108-1711 (1 × 10^5.0TCID₅₀/_mL). The results showed that antibodies against specific PRRSVs in 5 of 5 immunized piglets were positive after a 14-day post-vaccination and did not develop fever or clinical diseases after NADC30-like PRRSV challenges. Additionally, compared with challenge control piglets, vaccinated piglets gained significantly more weight and showed much milder pathological lesions. Furthermore, the viral replication levels of the immunized group were significantly lower than those of the challenge control group. These results demonstrate that lineage 1 PRRSV SD-R is a good candidate for an efficacious vaccine, providing complete clinical protection for piglets against NADC30-like PRRSVs.