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.

Tibetan pig is a unique pig breed native to the Qinghai–Tibet Plateau. To investigate viral communities associated with porcine respiratory disease complex (PRDC), 167 respiratory samples were collected from Tibetan pigs in the Ganzi Tibetan autonomous prefecture of Sichuan province. Following library construction and Illunima Novaseq sequencing, 18 distinct viruses belonging to 15 viral taxonomic families were identified in Tibetan pigs with PRDC. Among the 18 detected viruses, 3 viruses were associated with PRDC, including porcine circovirus type 2 (PCV-2), Torque teno sus virus (TTSuV), and porcine cytomegalovirus (PCMV). The genomic sequences of two PCV-2 strains, three TTSuV strains, and one novel Porprismacovirus strain were assembled by SOAPdenovo software (v2). Sequence alignment and phylogenetic analysis showed that both PCV-2 strains belonged to PCV-2d, three TTSuVs were classified to TTSuV2a and TTSuV2b genotypes, and the Porprismacovirus strain PPMV-SCgz-2022 showed a close genetic relationship with a virus of human origin. Recombination analysis indicated that PPMV-SCgz-2022 may have originated from recombination events between Human 16,806 × 66-213 strain and Porcine 17,668 × 82-593 strain. Furthermore, the high proportion of single infection or co-infection of PCV2/TTSuV2 provides insight into PRDC infection in Tibetan pigs. This is the first report of the viral communities in PRDC-affected Tibetan pigs in this region, and the results provides reference for the prevention and control of respiratory diseases in these animals.

Objective: A novel Bovine adenovirus type 3 (BAdV-3) with a natural deletion partial fiber gene was isolated in 2020 and named BO/YB24/17/CH. The objective of this study was to understand the pathogenicity of this virus.Methods: Thiry-two 3-week-old BALB/c mice were divided into three experimental groups and a control group. Mice in the experimental groups were intranasally inoculated with virus, and mice in the control group were inoculated with MDBK cell supernatant. Mice were weighed and clinically examined daily for appearance of any clinical signs. Three infected mice and one control mouse were euthanized at 1, 3, 5, 7, 9, 11, 13, and 15 days after inoculation. Tissue samples were collected for histopathological examination, immunohistochemical staining, and detection of the replication dynamics of virus.Results: All infected mice developed mild clinical signs such as lethargy, weight loss, loss of appetite, and a rough hair coat, and gross lesions were observed as pulmonary punctate hemorrhage, lobular atrophy and splenomegaly. Histopathological examination revealed thickening of alveolar septa and mildly dilated splenic nodules and blurred red-white medullary demarcation in the spleen. Immunohistochemical results further confirmed that the production of the above lesions was due to viral infection. Importantly, unlike previously reported BAdV-3 detection only in the lungs and trachea, this isolate could be detected in multiple organs such as the heart, liver, spleen, kidney, and even blood by virus isolation and titration and real-time PCR methods.Clinical significance: This study provides further insight into the pathogenicity of the fiber region deletion strain BO/YB24/17/CH in BALB/c mice, which provides a reference for the prevention and control of BAdV-3 as well as the development of vaccines.

Porcine reproductive and respiratory syndrome (PRRS), caused by porcine reproductive and respiratory syndrome virus (PRRSV), is a major infectious disease that poses a severe threat to the global swine industry. To investigate the role of miRNAs in the infection and susceptibility of PRRSV, four miRNA libraries were constructed and sequenced from PRRSV-infected and mock-infected of Tibetan pigs and Large White pigs at 7 days post-infection. A novel miRNA, miR-novel-80, was differentially expressed between PRRSV-infected and mock-infected porcine alveolar macrophages from 2 pig breeds. Importantly, the over-expression of miR-novel-80 inhibited the replication of a PRRSV-1 strain and multiple lineages (L1, L5, and L8) of PRRSV-2 strains in a dose-dependent manner. Bioinformatic predictions and experimental validation demonstrated that miR-novel-80 restricts viral replication through a dual antiviral mechanism. Directly, it targets the PRRSV nsp1-coding region within the ORF1a to suppress viral proliferation. Indirectly, miR-novel-80 specifically down-regulates the expression of host factor CXXC finger protein 4 (CXXC4). This reduction relieves the suppression of the Wnt/β-catenin signaling pathway, which in turn activates NF-κB-dependent innate immune responses to further inhibit PRRSV infection. Collectively, this study investigates the biological characteristics of miR-novel-80 and unveils its underlying molecular mechanisms in restricting PRRSV infection in vitro. However, its biological function and anti-PRRSV therapeutic effect in vivo need further investigation.

Background: 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. This study aimed to analyze the genetic features and investigate the pathogenicity of a novel NADC34-like PRRSV in southwest China. Results: In this study, 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. Evolutionary analyses conducted on ORF5 sequences using Bayesian phylodynamic models estimated the time of emergence of NADC34-like strains in China was as early as July 2013, not long before its first detection in the United States in 2014. 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.Conclusions: This is the first report of the emergence of a novel highly pathogenic NADC34-like recombinant strain, and it highlights the importance of monitoring newly emerging PRRSV strains in China.

Porcine reproductive and respiratory syndrome (PRRS), caused by PRRS virus (PRRSV), poses a serious threat to the global swine industry. Although modified live virus (MLV) vaccines have been widely used in the field for PRRS prevention for decades, the safety and efficacy of these vaccines have long been controversial. Here, we report a rare recombination pattern in China: the emergence of a novel NADC30-like PRRSV strain recombined from two MLV-like strains. Genome comparative analysis reveals that the SCMS2025 isolate has a non-continuous 136-amino acid deletion in the NSP2 protein and shares the highest nucleotide identity of 87.6% with lineage 5 (L5) strains. Phylogenetic analysis showed that SCMS2025 was classified into L1 (NADC30-like) strains based on ORF5 genotyping, whereas it belonged to a single branch between L1 and L5 strains based on the complete genomic sequences. Strikingly, genomic recombination analysis revealed that the newly emerged PRRSV isolate likely resulted from complex recombination events between NADC30-like and two MLV-like strains (RespPRRS MLV and TJbd14-1 MLV-like strains). Furthermore, SCMS2025 infection caused transient overt clinical signs followed by rapid recovery, indicating that the novel PRRSV isolate is a low pathogenic strain. Notably, all SCMS2025-inoculated piglets remained seronegative for PRRSV-specific antibodies throughout the entire 14-day observation period, suggesting a delayed onset of the host humoral immune response. Our study provides evidence for the ongoing evolution of PRRSV through inter lineage recombination and highlights the urgent need for safe and effective vaccines.