Identification of Conserved Amino Acid Substitutions During Serial Infection of Pregnant Cattle and Sheep With Bovine Viral Diarrhea Virus

Non-cytopathic bovine viral diarrhea virus (BVDV) inhibits innate immune responses via induction of mitophagy

Bovine viral diarrhea virus (BVDV) belongs to the genus Pestivirus within the family Flaviviridae. Mitophagy plays important roles in virus-host interactions. Here, we provide evidence that non-cytopathic (NCP) BVDV shifts the balance of mitochondrial dynamics toward fission and induces mitophagy to inhibit innate immune responses. Mechanistically, NCP BVDV triggers the translocation of dynamin-related protein (Drp1) to mitochondria and stimulates its phosphorylation at Ser616, leading to mitochondrial fission. In parallel, NCP BVDV-induced complete mitophagy via Parkin-dependent pathway contributes to eliminating damaged mitochondria to inhibit MAVS- and mtDNA-cGAS-mediated innate immunity responses, mtROS-mediated inflammatory responses and apoptosis initiation. Importantly, we demonstrate that the LIR motif of ERNS is essential for mitophagy induction. In conclusion, this study is the first to show that NCP BVDV-induced mitophagy plays a central role in promoting cell survival and inhibiting innate immune responses in vitro.

Mitochondria-mediated ferroptosis contributes to the inflammatory responses of bovine viral diarrhea virus (BVDV) in vitro

Bovine viral diarrhea virus (BVDV) belongs to the family Flaviviridae and includes two biotypes in cell culture: cytopathic (CP) or non-cytopathic (NCP) effects. Ferroptosis is a non-apoptotic form of programmed cell death that contributes to inflammatory diseases. However, whether BVDV induces ferroptosis and the role of ferroptosis in viral infection remain unclear. Here, we provide evidence that both CP and NCP BVDV can induce ferroptosis in Madin-Darby bovine kidney cells at similar rate. Mechanistically, biotypes of BVDV infection downregulate cytoplasmic and mitochondrial GPX4 via Nrf2-GPX4 pathway, thereby resulting in lethal lipid peroxidation and promoting ferroptosis. In parallel, BVDV can degrade ferritin heavy chain and mitochondrial ferritin via NCOA4-mediated ferritinophagy to promote the accumulation of Fe2+ and initiate ferroptosis. Importantly, CP BVDV-induced ferroptosis is tightly associated with serious damage of mitochondria and hyperactivation of inflammatory responses. In contrast, mild or unapparent damage of mitochondria and slight inflammatory responses were detected in NCP BVDV-infected cells. More importantly, different mitophagy pathways in response to mitochondria damage by both biotypes of BVDV are involved in inflammatory responses. Overall, this study is the first to show that mitochondria may play key roles in mediating ferroptosis and inflammatory responses induced by biotypes of BVDV in vitro.IMPORTANCEBovine viral diarrhea virus (BVDV) threatens a wide range of domestic and wild cattle population worldwide. BVDV causes great economic loss in cattle industry through its immunosuppression and persistent infection. Despite extensive research, the mechanism underlying the pathogenesis of BVDV remains elusive. Our data provide the first direct evidence that mitochondria-mediated ferroptosis and mitophagy are involved in inflammatory responses in both biotypes of BVDV-infected cells. Importantly, we demonstrate that the different degrees of injury of mitochondria and inflammatory responses may attribute to different mitophagy pathways induced by biotypes of BVDV. Overall, our findings uncover the interaction between BVDV infection and mitochondria-mediated ferroptosis, which shed novel light on the physiological impacts of ferroptosis on the pathogenesis of BVDV infection, and provide a promising therapeutic strategy to treat this important infectious disease with a worldwide distribution.

Molecular Characteristics of Bovine Viral Diarrhea Virus Strains Isolated from Persistently Infected Cattle

In this study, we reported the isolation, identification, and molecular characteristics of nine BVDV strains that were isolated from the serum of persistently infected cattle. The new strains were designated as BVDV TJ2101, TJ2102, TJ2103, TJ2104, TJ2105, TJ2106, TJ2107, TJ2108 and TJ2109. The TJ2102 and TJ2104 strains were found to be cytopathic BVDV, and the other strains were non-cytopathic BVDV. An alignment and phylogenetic analysis showed that the new isolates share 92.2-96.3% homology with the CP7 strain and, thus, were classified as the BVDV-1b subgenotype. A recombination analysis of the genome sequences showed that the new strains could be recombined by the major parent BVDV-1a NADL strain and the minor parent BVDV-1m SD-15 strain. Some genome variations or unique amino acid mutations were found in 5'-UTR, E0 and E2 of these new isolates. In addition, a potential linear B cell epitopes prediction showed that the potential linear B cell epitope at positions 56-61 is highly variable in BVDV-1b. In conclusion, the present study has identified nine strains of BVDV from persistently infected cattle in China. Further studies on the virulence and pathogenesis of these new strains are recommended.

A Novel Method for Training the Interdiction of Restricted and Hazardous Biological Materials by Detection Dogs

The interdiction of restricted and hazardous biological agents presents challenges for any detection method due to the inherent complexity of sample type and accessibility. Detection capabilities for this category of agents are limited and restricted in their mobility, adaptability and efficiency. The potential for identifying biological agents through a volatile organic compound (VOC) signature presents an opportunity to use detection dogs in a real-time mobile capacity for surveillance and screening strategies. However, the safe handling and access to the materials needed for training detection dogs on restricted or hazardous biological agents prevents its broader application in this field. This study evaluated the use of a polymer-based training aid in a viral detection model using bovine viral diarrhea virus mimicking biosafety level 3+ agent conditions. After the biological agent-based odor was absorbed into the polymer, the aid was rendered safe for handling through a rigorous sterilization process. The viral culture-based training aid was then used to train a cohort of detection dogs (n = 6) to discriminate agent-based target odor in culture from relevant distractor odors including non-target biological agent-based odors. Following culture-based training, dogs were tested for generalization to aids with infected animal sample-based odors across five sample types (fecal, blood, nasal, saliva, and urine). Within the context of the polymer-based training aid system, dogs were successfully trained to detect and discriminate a representative biological viral agent-based odor from distractor odors with a 97.22% (±2.78) sensitivity and 97.11% (±1.94) specificity. Generalization from the agent-based odor to sample-based odors ranged from 65.40% (±8.98) to 91.90 % (±6.15) sensitivity and 88.61% (±1.46) to 96.00% (±0.89) specificity across the sample types. The restrictive nature for mimicking the access and handling of a BSL 3+ agent presented challenges that required a strict study design uncommon to standard detection dog training and odor presentation. This study demonstrates the need to further evaluate the utility and challenges of training detection dogs to alert to biological samples using safe and manageable training aids.

Recent Advances on the Bovine Viral Diarrhea Virus Molecular Pathogenesis, Immune Response, and Vaccines Development

The bovine viral diarrhea virus (BVDV) consists of two species and various subspecies of closely related viruses of varying antigenicity, cytopathology, and virulence-induced pathogenesis. Despite the great ongoing efforts to control and prevent BVDV outbreaks and the emergence of new variants, outbreaks still reported throughout the world. In this review, we are focusing on the molecular biology of BVDV, its molecular pathogenesis, and the immune response of the host against the viral infection. Special attention was paid to discuss some immune evasion strategies adopted by the BVDV to hijack the host immune system to ensure the success of virus replication. Vaccination is one of the main strategies for prophylaxis and contributes to the control and eradication of many viral diseases including BVDV. We discussed the recent advances of various types of currently available classical and modern BVDV vaccines. However, with the emergence of new strains and variants of the virus, it is urgent to find some other novel targets for BVDV vaccines that may overcome the drawbacks of some of the currently used vaccines. Effective vaccination strategy mainly based on the preparation of vaccines from the homologous circulating strains. The BVDV-E2 protein plays important role in viral infection and pathogenesis. We mapped some important potential neutralizing epitopes among some BVDV genomes especially the E2 protein. These novel epitopes could be promising targets against the currently circulating strains of BVDV. More research is needed to further explore the actual roles of these epitopes as novel targets for the development of novel vaccines against BVDV. These potential vaccines may contribute to the global eradication campaign of the BVDV.

Decrypting the Origin and Pathogenesis in Pregnant Ewes of a New Ovine Pestivirus Closely Related to Classical Swine Fever Virus

This study shows the origin and the pathogenic role of a novel ovine pestivirus (OVPV) isolated in 2017 in Italy, as a pathogenic agent causing severe abortions after infection in pregnant ewes and high capacity for virus trans-placental transmission as well as the birth of lambs suffering OVPV-persistent infection. The OVPV infection induced early antibody response detected by the specific ELISA against classical swine fever virus (CSFV), another important virus affecting swine. The neutralizing antibody response were similar against CSFV strains from genotype 2 and the OVPV. These viruses showed high identity in the B/C domain of the E2-glycoprotein. Close molecular diagnostics cross-reactivity between CSFV and OVPV was found and a new OVPV molecular assay was developed. The phylodynamic analysis showed that CSFV seems to have emerged as the result of an inter-species jump of Tunisian sheep virus (TSV) from sheep to pigs. The OVPV and the CSFV share the TSV as a common ancestor, emerging around 300 years ago. This suggests that the differentiation of TSV into two dangerous new viruses for animal health (CSFV and OVPV) was likely favored by human intervention for the close housing of multiple species for intensive livestock production.

Bovine viral diarrhea virus: An updated American College of Veterinary Internal Medicine consensus statement with focus on virus biology, hosts, immunosuppression, and vaccination

Control of bovine viral diarrhea virus (BVDV) in cattle populations across most of the world has remained elusive in spite of advances in knowledge about this viral pathogen. A central feature of virus perseverance in cattle herds is the unique mechanism of persistent infection. Managing BVDV infection in herds involves controlling persistently infected carrier animals using a multidimensional approach of vaccination, biosecurity, and identification of BVDV reservoirs. A decade has passed since the original American College of Veterinary Internal Medicine consensus statement on BVDV. While much has remained the same with respect to clinical signs of disease, pathogenesis of infection including persistent infection, and diagnosis, scientific articles published since 2010 have led to a greater understanding of difficulties associated with control of BVDV. This consensus statement update on BVDV presents greater focus on topics currently relevant to the biology and control of this viral pathogen of cattle, including changes in virus subpopulations, infection in heterologous hosts, immunosuppression, and vaccination.

Changes Introduced in the Open Reading Frame of Bovine Viral Diarrhea Virus During Serial Infection of Pregnant Swine

Bovine viral diarrhea virus (BVDV) is one of the most economically important viruses of cattle, but this pathogen is also able to infect pigs, camelids, and a wide range of domestic and wild ruminants. BVDV isolates circulating in animal populations are genetically and antigenically highly diverse. Acute BVDV infections in cattle cause the introduction of many substitutions in the viral genome. Serial infection of pregnant sheep with a BVDV-1b isolate of bovine origin was also associated with great numbers of substitutions. To our knowledge, genomic changes arising during BVDV infections in swine have not been investigated. The purpose of this study was to investigate the changes occurring in the open reading frame (ORF) of BVDV during serial infection of pregnant swine with a BVDV isolate of bovine origin. The BVDV-1b isolate AU526 was serially passaged in six pregnant gilts, two of which gave birth to live piglets congenitally infected with BVDV. The complete ORF sequences of 14 BVDV isolates obtained from pregnant gilts and their piglets were determined. Their analysis revealed that serial transmission of AU526 in pregnant swine resulted in many genomic changes. All isolates of porcine origin shared 32 nucleotide and 12 amino acid differences with the virus inoculum AU526. These changes were detected after a single passage in pregnant swine and were conserved during the subsequent five passages. Amino acid changes occurred primarily in genomic regions encoding the BVDV structural proteins E2 and E ^rns . These results suggest that BVDV infections in pregnant swine may contribute significantly to the genetic variability of BVDV and lead to the appearance of adaptive changes.

Bovine viral diarrhoea virus loses quasispecies diversity rapidly in culture

Bovine viral diarrhoea (BVD) is an important disease of cattle, with significant impacts on animal health and welfare. The wide host range of the causative pestiviruses may lead to formation of virus reservoirs in other ruminant or wildlife species, presenting a concern for the long-term success of BVD eradication campaigns. It is likely that the quasispecies nature of these RNA viruses contributes to their interspecies transmission by providing genetic plasticity. Understanding the spectrum of sequence variants present in persistently infected (PI) animals is, therefore, essential for studies of virus transmission. To analyse quasispecies diversity without amplification bias, we extracted viral RNA from the serum of a PI cow, and from cell culture fluid after three passages of the same virus in culture, to produce cDNA without amplification. Sequencing of this material using Illumina 250 bp paired-read technology produced full-length virus consensus sequences from both sources and demonstrated the quasispecies diversity of this pestivirus A genotype 1a field strain within serum and after culture. We report the distribution and diversity of over 800 SNPs and provide evidence for a loss of diversity after only three passages in cell culture, implying that cultured viruses cannot be used to understand quasispecies diversity and may not provide reliable molecular markers for source tracing or transmission studies. Additionally, both serum and cultured viruses could be sequenced as a set of 25 overlapping PCR amplicons that demonstrated the same consensus sequences and the presence of many of the same quasispecies variants. The observation that aspects of the quasispecies structure revealed by massively parallel sequencing are also detected after PCR and Sanger sequencing suggests that this approach may be useful for small or difficult to analyse samples.

PD-1-Mediated PI3K/Akt/mTOR, Caspase 9/Caspase 3 and ERK Pathways Are Involved in Regulating the Apoptosis and Proliferation of CD4+ and CD8+ T Cells During BVDV Infection in vitro

Acute infection of bovine viral diarrhea virus (BVDV) is associated with immune dysfunction and can cause peripheral blood lymphopenia and lymphocyte apoptosis. Our previous study has confirmed that programmed death-1 (PD-1) blockade inhibits peripheral blood lymphocyte (PBL) apoptosis and restores proliferation and anti-viral immune functions of lymphocytes after BVDV infection in vitro. However, the immunomodulatory effects of PD-1 pathway on major PBL subsets are unclear and their underlying molecular mechanisms need to be further studied. Therefore, in this study, we examined PD-1 expression in bovine PBL subsets after BVDV infection in vitro and analyzed the effects of PD-1 blockade on the apoptosis and proliferation of CD4⁺ and CD8⁺ T cells and expression of PD-1 downstream signaling molecules. The results showed that PD-1 expression was enhanced on CD4⁺ and CD8⁺ T cells, but not on CD21⁺ B cells after cytopathic (CP) BVDV (strain NADL) and non-cytopathic (NCP) BVDV (strain KD) infection in vitro and PD-1 blockade significantly reduced the apoptosis of CD4⁺ and CD8⁺ T cells after these two strains infection. Remarkably, PD-1 blockade significantly increased the proliferation of CD4⁺ and CD8⁺ T cells after CP BVDV infection, but only significantly increased the proliferation of CD4⁺ T cells after NCP BVDV infection. In addition, we confirmed that PD-1-mediated PI3K/Akt/mTOR, caspase 9/caspase 3 and ERK pathways are involved in regulating the apoptosis and proliferation of CD4⁺ and CD8⁺ T cells during BVDV infection in vitro. Notably, ERK is involved in the regulation mechanism PD-1 mediated only when the cells are infected with CP BVDV. Our findings provide a scientific basis for exploring the molecular mechanism of immune dysfunction caused by acute BVDV infection.

RNA-Seq-based transcriptomic profiling of primary interstitial cells of Cajal in response to bovine viral diarrhea virus infection

Infections with bovine viral diarrhea virus (BVDV) contribute significantly to health-related economic losses in the beef and dairy industries and are widespread throughout the world. Severe acute BVDV infection is characterized by a gastrointestinal (GI) inflammatory response. The mechanism of inflammatory lesions caused by BVDV remains unknown. The interstitial cells of Cajal (ICC) network plays a pivotal role as a pacemaker in the generation of electrical slow waves for GI motility, and it is crucial for the reception of regulatory inputs from the enteric nervous system. The present study investigated whether ICC were a good model for studying GI inflammatory lesions caused by BVDV infection. Primary ICC were isolated from the duodenum of Merino sheep. The presence of BVDV was detected in ICC grown for five passages after BVDV infection, indicating that BVDV successfully replicated in ICC. After infection with BVDV strain TC, the cell proliferation proceeded slowly or declined. Morphological changes, including swelling, dissolution, and formation of vacuoles in the ICC were observed, indicating quantitative, morphological and functional changes in the cells. RNA sequencing (RNA-Seq) was performed to investigate differentially expressed genes (DEGs) in BVDV-infected ICC and explore the molecular mechanism of underlying quantitative, morphological and functional changes of ICC. Eight hundred six genes were differentially expressed after BVDV infection, of which 538 genes were upregulated and 268 genes were downregulated. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that the 806 DEGs were significantly enriched in 27 pathways, including cytokine-cytokine receptor interaction, interleukin (IL)-17 signaling and mitogen-activated protein kinase (MAPK) signaling pathways. The DEGs and raw files of high-throughput sequencing of this study were submitted to the NCBI Gene Expression Omnibus (GEO) database (accession number GSE122344). Finally, 21 DEGs were randomly selected, and the relative repression levels of these genes were tested using the quantitative real-time PCR (qRT-PCR) to validate the RNA-Seq results. The results showed that the related expression levels of 21 DEGs were similar to RNA-Seq. This study is the first to establish a new infection model for investigating GI inflammatory lesions induced by BVDV infection. RNA-Seq-based transcriptomic profiling can provide a basis for study on BVDV-associated inflammatory lesions.