Novel pseudorabies virus variant with defects in TK, gE and gI protects growing pigs against lethal challenge

pUS6 in pseudorabies virus participates in the process of inhibiting antigen presentation by inhibiting the assembly of peptide loading complex

Pseudorabies virus (PRV) can establish lifelong latent infection in peripheral nervous ganglion, and persistent infections in peripheral blood lymphocytes. Establishing an infection in the lymphocytes does not only enable the PRV to escape host immune surveillance but pass through the placental barrier, leading to fetal death and abortion. Due to the pathogenicity of the PRV, it poses a huge challenge in its prevention and control. The PRV escapes host immunity through downregulation of swine leukocyte antigen class I (SLA I) molecules on infected cells. However, data on the molecular mechanisms of the SLA I suppression remains scant. Here, in order to verify the effect of candidate proteins PRV pUL44 and pUS6 on PRV immune escape related molecules SLA I and peptide loading complex (PLC), we detected the expression of SLA I and PLC components after expressing PRV pUL44 and pUS6. The effects of pUS6 and pUL44 on SLA I and PLC were analyzed by qRT-PCR and Western blot at mRNA and protein level, respectively. Cells expressing pUS6 or pUL44 genes showed a significantly suppressed expression of surface and total SLA I molecules. In addition, unlike UL44, the US6 gene was shown to downregulate the transporter associated with antigen processing 1 (TAP1), TAP2 and Tapasin molecules. The results show that PRV pUS6 may participate in virus immune escape by directly regulating the SLA I, TAP dimer and Tapasin molecules, thus blocking the transportation of TAP-bound peptides to the ER to bind SLA I molecules. We provide a theoretical basis on the mechanism of TAP mediated immune escape by the PRV.

Pseudorabies Virus Glycoproteins E and B Application in Vaccine and Diagnosis Kit Development

Background: Pseudorabies virus (PRV) is a highly infectious pathogen that affects a wide range of mammals and imposes a significant economic burden on the global pig industry. The viral envelope of PRV contains several glycoproteins, including glycoprotein E (gE) and glycoprotein B (gB), which play critical roles in immune recognition, vaccine development, and diagnostic procedures. Mutations in these glycoproteins may enhance virulence, highlighting the need for updated vaccines. Method: This review examines the functions of PRV gE and gB in vaccine development and diagnostics, focusing on their roles in viral replication, immune system interaction, and pathogenicity. Additionally, we explore recent findings on the importance of gE deletion in attenuated vaccines and the potential of gB to induce immunity. Results: Glycoprotein E (gE) is crucial for the virus's axonal transport and nerve invasion, facilitating transmission to the central nervous system. Deletion of gE is a successful strategy in vaccine development, enhancing the immune response. Glycoprotein B (gB) plays a central role in viral replication and membrane fusion, aiding viral spread. Mutations in these glycoproteins may increase PRV virulence, complicating vaccine efficacy. Conclusion: With PRV glycoproteins being essential to both vaccine development and diagnostic approaches, future research should focus on enhancing these components to address emerging PRV variants. Updated vaccines and diagnostic tools are critical for combating new, more virulent strains of PRV.

Breaking Latent Infection: How ORF37/38-Deletion Mutants Offer New Hope against EHV-1 Neuropathogenicity

Equid alphaherpesvirus 1 (EHV-1) has been linked to the emergence of neurological disorders, with the horse racing industry experiencing significant impacts from outbreaks of equine herpesvirus myeloencephalopathy (EHM). Building robust immune memory before pathogen exposure enables rapid recognition and elimination, preventing infection. This is crucial for effectively managing EHV-1. Removing neuropathogenic factors and immune evasion genes to develop live attenuated vaccines appears to be a successful strategy for EHV-1 vaccines. We created mutant viruses without ORF38 and ORF37/38 and validated their neuropathogenicity and immunogenicity in hamsters. The ∆ORF38 strain caused brain tissue damage at high doses, whereas the ∆ORF37/38 strain did not. Dexamethasone was used to confirm latent herpesvirus infection and reactivation. Dexamethasone injection increased viral DNA load in the brains of hamsters infected with the parental and ∆ORF38 strains, but not in those infected with the ∆ORF37/38 strain. Immunizing hamsters intranasally with the ∆ORF37/38 strain as a live vaccine produced a stronger immune response compared to the ∆ORF38 strain at the same dose. The hamsters demonstrated effective protection against a lethal challenge with the parental strain. This suggests that the deletion of ORF37/38 may effectively inhibit latent viral infection, reduce the neuropathogenicity of EHV-1, and induce a protective immune response.

The inhibitory effect of swine TAB1 on the replication of pseudorabies virus

TAK1-binding protein 1 (TAB1) assembles with TAK1 through its C-terminal domain, leading to the self-phosphorylation and activation of TAK1, which plays an important role in the activation of NF-κB and MAPK signaling pathway. Pseudorabies virus (PRV) is the pathogen of Pseudorabies (PR), which belongs to the Alphaherpesvirus subfamily and causes serious economic losses to the global pig industry. However, the impact of swine TAB1 (sTAB1) on PRV infection has not been reported. In this study, evidence from virus DNA copies, virus titer and western blotting confirmed that sTAB1 could inhibit PRV replication and knockout of sTAB1 by CRISPR-Cas9 gene editing system could promote PRV replication. Further mechanistic studies by real-time PCR and luciferase reporter gene assay demonstrated that sTAB1 could enhance the production of inflammatory factors and chemokines, IFN-β transcription level and IFN-β promoter activity after PRV infection. In summary, we clarify the underlying mechanism of sTAB1 in inhibiting PRV replication for the first time, which provides a new idea for preventing PRV infection and lays a foundation for PRV vaccine development.

Pseudorabies virus UL13 primes inflammatory response through downregulating heat shock factor 1

Pseudorabies virus is a swine alpha-herpesvirus. We demonstrated that alpha-herpesvirus infection downregulates HSF1, a master transcription factor in the heat shock response. The serine/threonine protein kinase activity of late viral protein UL13 is indispensable for HSF1 depletion and phosphorylation, and UL13 does not degrade HSF1 posttranslationally but inhibits the HSF1 mRNA level. Importantly, UL13 increased HSF1 activity even though it reduced HSF1 mRNA. Furthermore, viral replication markedly decreased in the HSF1 knockout cell line or in the presence of an HSF1-specific inhibitor. Interestingly, HSF1 knockout accelerated the activation of NF-κB and p38MAPK. The K96 loci of UL13 are important to induce high levels of IL-6, TNF-α, and IL-β cytokines while playing a crucial role in promoting mild interstitial pneumonia, liver necrosis, and severe inflammatory cell infiltration in the footpad. Thus, UL13 steers the heat shock response to promote viral replication and the inflammatory response. IMPORTANCE: PRV is a ubiquitous pathogen that infects a variety of mammals, such as pigs, ruminants, carnivores, and rodents as well as human beings, causing enormous economic losses in the swine industry. Here, we employed PRV as a model to determine the relationship between α-herpesvirus and the inflammatory response. Overall, our findings indicated that PRV infection inhibits the level of HSF1 mRNA via the serine/threonine protein kinase activity of UL13. Additionally, we discovered that HSF1 was involved in NF-κB activation upon PRV infection. PRV UL13 orchestrates the level of HSF1 mRNA, HSF1 protein phosphorylation, and priming of the inflammatory response. Our study reveals a novel mechanism employed by UL13 serine/threonine protein kinase activity to promote the inflammatory response, providing novel clues for therapy against alpha-herpesvirus infection.

Pseudorabies virus infection increases the permeability of the mammalian respiratory barrier to facilitate Pasteurella multocida infection

Interaction between viruses and bacteria during the development of infectious diseases is a complex question that requires continuous study. In this study, we explored the interactions between pseudorabies virus (PRV) and Pasteurella multocida (PM), which are recognized as the primary and secondary agents of porcine respiratory disease complex (PRDC), respectively. In vivo tests using mouse models demonstrated that intranasal inoculation with PRV at a sublethal dose induced disruption of murine respiratory barrier and promoted the invasion and damages caused by PM through respiratory infection. Inoculation with PRV also disrupted the barrier function of murine and porcine respiratory epithelial cells, and accelerated the adherence and invasion of PM to the cells. In mechanism, PRV infection resulted in decreased expression of tight junction proteins (ZO-1, occludin) and adherens junction proteins (β-catenin, E-cadherin) between neighboring respiratory epithelial cells. Additionally, PRV inoculation at an early stage downregulated multiple biological processes contributing to epithelial adhesion and barrier functions while upregulating signals beneficial for respiratory barrier disruption (e.g., the HIF-1α signaling). Furthermore, PRV infection also stimulated the upregulation of cellular receptors (CAM5, ICAM2, ACAN, and DSCAM) that promote bacterial adherence. The data presented in this study provide insights into the understanding of virus-bacteria interactions in PRDC and may also contribute to understanding the mechanisms of secondary infections caused by different respiratory viruses (e.g., influenza virus and SARS-CoV-2) in both medical and veterinary medicine.

IMPORTANCE

Co-infections caused by viral and bacterial agents are common in both medical and veterinary medicine, but the related mechanisms are not fully understood. This study investigated the interactions between the zoonotic pathogens PRV and PM during the development of respiratory infections in both cell and mouse models, and reported the possible mechanisms which included: (i) the primary infection of PRV may induce the disruption and/or damage of mammal respiratory barrier, thereby contributing to the invasion of PM; (ii) PRV infection at early stage accelerates the transcription and/or expression of several cellular receptors that are beneficial for bacterial adherence. This study may shed a light on understanding the mechanisms on the secondary infection of PM promoted by different respiratory viruses (e.g., influenza virus and SARS-CoV-2) in both medical and veterinary medicine.

Pathogenicity characteristics of different subgenotype pseudorabies virus in newborn piglets

Pseudorabies virus is a major pathogen in the pig industry, causing substantial economic losses. The emergence of pseudorabies virus variant strains in China has led to extensive spread, raising concerns about their potential impact. However, the differences in pathogenicity between the classical strains and the variant strains of genotype II are not well understood. In this study, we isolated three pseudorabies virus strains to evaluate their replication characteristics and to examine the differences in virulence genes among various subgenotypes strains. Additionally, a piglet infection model was utilized to investigate the clinical features of infection, tissue tropism, and the inflammatory responses induced by these strains. Our results showed that the genotype II variant strains (MS, XJ, LS, and CZ) had significantly larger plaque sizes and higher replication capacities than the genotype II classical strain Fa. The animal experiments revealed significant differences in pathogenicity among the pseudorabies virus subgenotype strains, with the variant strains showing higher mortality rates, more severe clinical symptoms, increased nasal virus shedding, and a more robust inflammatory response compared to the genotype II classical strain. There were also notable differences in tissue tropism among the strains. In terms of tissue viral loads, the genotype II variant strains did not exhibit a significant advantage over the genotype I classical strain. Furthermore, our findings indicate that antibodies against the genotype II classical strains have a reduced neutralizing capacity against the genotype II variant strains. On the other hand, antibodies against the genotype II variant strains displayed similar neutralizing abilities against both classical and variant strains. Overall, these findings offer important insights into the distinctions among pseudorabies virus subgenotypes and their implications for the clinical control of pseudorabies virus infections in pig farming.

Immunological characteristics of a recombinant alphaherpesvirus with an envelope-embedded Cap protein of circovirus

Introduction

Variant pseudorabies virus (PRV) is a newly emerged zoonotic pathogen that can cause human blindness. PRV can take advantage of its large genome and multiple non-essential genes to construct recombinant attenuated vaccines carrying foreign genes. However, a major problem is that the foreign genes in recombinant PRV are only integrated into the genome for independent expression, rather than assembled on the surface of virion.

Methods

We reported a recombinant PRV with deleted gE/TK genes and an inserted porcine circovirus virus 2 (PCV2) Cap gene into the extracellular domain of the PRV gE gene using the Cre-loxP recombinant system combined with the CRISPR-Cas9 gene editing system. This recombinant PRV (PRV-Cap), with the envelope-embedded Cap protein, exhibits a similar replication ability to its parental virus.

Results

An immunogenicity assay revealed that PRV-Cap immunized mice have 100% resistance to lethal PRV and PCV2 attacks. Neutralization antibody and ELISPOT detections indicated that PRV-Cap can enhance neutralizing antibodies to PRV and produce IFN-γ secreting T cells specific for both PRV and PCV2. Immunological mechanistic investigation revealed that initial immunization with PRV-Cap stimulates significantly early activation and expansion of CD69+ T cells, promoting the activation of CD4 Tfh cell dependent germinal B cells and producing effectively specific effector memory T and B cells. Booster immunization with PRV-Cap recalled the activation of PRV-specific IFN-γ+IL-2+CD4+ T cells and IFN-γ+TNF-α+CD8+ T cells, as well as PCV2-specific IFN-γ+TNF-α+CD8+ T cells.

Conclusion

Collectively, our data suggested an immunological mechanism in that the recombinant PRV with envelope-assembled PCV2 Cap protein can serve as an excellent vaccine candidate for combined immunity against PRV and PCV2, and provided a cost-effective method for the production of PRV- PCV2 vaccine.

Development of a live attenuated vaccine candidate for equid alphaherpesvirus 1 control: a step towards efficient protection

Equid alphaherpesvirus 1 (EqAHV1) is a viral pathogen known to cause respiratory disease, neurologic syndromes, and abortion storms in horses. Currently, there are no vaccines that provide complete protection against EqAHV1. Marker vaccines and the differentiation of infected and vaccinated animals (DIVA) strategy are effective for preventing and controlling outbreaks but have not been used for the prevention of EqAHV1 infection. Glycoprotein 2 (gp2), located on the envelope of viruses (EqAHV1), exhibits high antigenicity and functions as a molecular marker for DIVA. In this study, a series of EqAHV1 mutants with deletion of gp2 along with other virulence genes (TK, UL24/TK, gI/gE) were engineered. The mutant viruses were studied in vitro and then in an in vivo experiment using Golden Syrian hamsters to assess the extent of viral attenuation and the immune response elicited by the mutant viruses in comparison to the wild-type (WT) virus. Compared with the WT strain, the YM2019 Δgp2, ΔTK/gp2, and ΔUL24/TK/gp2 strains exhibited reduced growth in RK-13 cells, while the ΔgI/gE/gp2 strain exhibited significantly impaired proliferation. The YM2019 Δgp2 strain induced clinical signs and mortality in hamsters. In contrast, the YM2019 ΔTK/gp2 and ΔUL24/TK/gp2 variants displayed diminished pathogenicity, causing no observable clinical signs or fatalities. Immunization with nasal vaccines containing YM2019 ΔTK/gp2 and ΔUL24/TK/gp2 elicited a robust immune response in hamsters. In particular, compared with the vaccine containing the ΔTK/gp2 strain, the vaccine containing the ΔUL24/TK/gp2 strain demonstrated enhanced immune protection upon challenge with the WT virus. Furthermore, an ELISA for gp2 was established and refined to accurately differentiate between infected and vaccinated animals. These results confirm that the ΔUL24/TK/gp2 strain is a safe and effective live attenuated vaccine candidate for controlling EqAHV1 infection.

Swine pseudorabies virus attenuated vaccine reprograms the kidney cancer tumor microenvironment and synergizes with PD-1 blockade

The global incidence rate of kidney cancer (KC) has been steadily increasing over the past 30 years. With the aging global population, kidney cancer has become an escalating concern that necessitates vigilant surveillance. Nowadays, surgical intervention remains the optimal therapeutic approach for kidney cancer, while the availability of efficacious treatments for advanced tumors remains limited. Oncolytic viruses, an emerging form of immunotherapy, have demonstrated encouraging anti-neoplastic properties and are progressively garnering public acceptance. However, research on oncolytic viruses in kidney cancer is relatively limited. Furthermore, given the high complexity and heterogeneity of kidney cancer, it is crucial to identify an optimal oncolytic virus agent that is better suited for its treatment. The present study investigates the oncolytic activity of the Pseudorabies virus live attenuated vaccine (PRV-LAV) against KC. The findings clearly demonstrate that PRV-LAV exhibits robust oncolytic activity targeting KC cell lines. Furthermore, the therapeutic efficacy of PRV-LAV was confirmed in both a subcutaneous tumor-bearing nude mouse model and a syngeneic mouse model of KC. Combined RNA-seq analysis and flow cytometry revealed that PRV-LAV treatment substantially enhances the infiltration of a diverse range of lymphocytes, including T cells, B cells, macrophages, and NK cells. Additionally, PRV-LAV treatment enhances T cell activation and exerts antitumor effects. Importantly, the combination of PRV-LAV with anti-PD-1 antibodies, an approved drug for KC treatment, synergistically enhances the efficacy against KC. Overall, the discovery of PRV-LAV as an effective oncolytic virus holds significant importance for improving the treatment efficacy and survival rates of KC patients.

Transcriptomic analysis reveals impact of gE/gI/TK deletions on host response to PRV infection

BACKGROUND

Pseudorabies virus (PRV) causes substantial losses in the swine industry worldwide. Attenuated PRV strains with deletions of immunomodulatory genes glycoprotein E (gE), glycoprotein I (gI) and thymidine kinase (TK) are candidate vaccines. However, the effects of gE/gI/TK deletions on PRV-host interactions are not well understood.

METHODS

To characterize the impact of gE/gI/TK deletions on host cells, we analyzed and compared the transcriptomes of PK15 cells infected with wild-type PRV (SD2017), PRV with gE/gI/TK deletions (SD2017gE/gI/TK) using RNA-sequencing.

RESULTS

The attenuated SD2017gE/gI/TK strain showed increased expression of inflammatory cytokines and pathways related to immunity compared to wild-type PRV. Cell cycle regulation and metabolic pathways were also perturbed.

CONCLUSIONS

Deletion of immunomodulatory genes altered PRV interactions with host cells and immune responses. This study provides insights into PRV vaccine design.

Pseudorabies gD protein protects mice and piglets against lethal doses of pseudorabies virus

Introduction

Pseudorabies (PR) is a highly contagious viral disease caused by the pseudorabies virus (PRV), which can cause disease in a wide range of domestic and wild animals. Studies have shown that new mutant strains have emerged in pig farms in many regions and that commercial inactivated and live attenuated vaccines are becoming less effective at protecting pigs.

Methods

Porcine pseudorabies glycoprotein D (gD) gene (GenBank: QEY95774.1) with hexa-His tag to the C terminus for further purification processes was cloned into the lentiviral expression plasmid pLV-CMV-eGFP by restriction enzyme, the resulting plasmid was designated as pLV-CMV-gD. HEK-293T cells with robust and stable expression of recombinant gD protein was established by infection with recombinant lentivirus vector pLV-CMV-gD. We expressed porcine pseudorabies virus gD protein using HEK-293T cells.

Results

We describe in this study that individual gD proteins produced by a mammalian cell expression system are well immunogenic and stimulate high levels of PRV-specific and neutralizing antibodies in mice and piglets. All mice and piglets survived lethal doses of PRV, significantly reducing the amount of PRV virus in piglets' lymph nodes, lungs, spleen, and other tissues. It also significantly reduced the time cycle and amount of viral excretion from piglets to the environment through the nasal and anal cavities.

Discussion

The results suggest that PRV gD protein is expected to be a potential candidate for the preparation of genetically engineered PR vaccines for the prevention of PRV infection and the control of PR epidemics.

The potential of swine pseudorabies virus attenuated vaccine for oncolytic therapy against malignant tumors

BACKGROUND

Oncolytic viruses are now well recognized as potential immunotherapeutic agents against cancer. However, the first FDA-approved oncolytic herpes simplex virus 1 (HSV-1), T-VEC, showed limited benefits in some patients in clinical trials. Thus, the identification of novel oncolytic viruses that can strengthen oncolytic virus therapy is warranted. Here, we identified a live-attenuated swine pseudorabies virus (PRV-LAV) as a promising oncolytic agent with broad-spectrum antitumor activity in vitro and in vivo.

METHODS

PRV cytotoxicity against tumor cells and normal cells was tested in vitro using a CCK8 cell viability assay. A cell kinase inhibitor library was used to screen for key targets that affect the proliferation of PRV-LAV. The potential therapeutic efficacy of PRV-LAV was tested against syngeneic tumors in immunocompetent mice, and against subcutaneous xenografts of human cancer cell lines in nude mice. Cytometry by time of flight (CyTOF) and flow cytometry were used to uncover the immunological mechanism of PRV-LAV treatment in regulating the tumor immune microenvironment.

RESULTS

Through various tumor-specific analyses, we show that PRV-LAV infects cancer cells via the NRP1/EGFR signaling pathway, which is commonly overexpressed in cancer. Further, we show that PRV-LAV kills cancer cells by inducing endoplasmic reticulum (ER) stress. Moreover, PRV-LAV is responsible for reprogramming the tumor microenvironment from immunologically naïve ("cold") to inflamed ("hot"), thereby increasing immune cell infiltration and restoring CD8+ T cell function against cancer. When delivered in combination with immune checkpoint inhibitors (ICIs), the anti-tumor response is augmented, suggestive of synergistic activity.

CONCLUSIONS

PRV-LAV can infect cancer cells via NRP1/EGFR signaling and induce cancer cells apoptosis via ER stress. PRV-LAV treatment also restores CD8+ T cell function against cancer. The combination of PRV-LAV and immune checkpoint inhibitors has a significant synergistic effect. Overall, these findings point to PRV-LAV as a serious potential candidate for the treatment of NRP1/EGFR pathway-associated tumors.

A self-assembled nanoparticle vaccine based on pseudorabies virus glycoprotein D induces potent protective immunity against pseudorabies virus infection

Pseudorabies virus (PRV) mainly causes pseudorabies (PR) or Aujeszky's disease in pigs and can infect humans, raising public health concerns about zoonotic and interspecies transmission of PR. With the emergence of PRV variants in 2011, the classic attenuated PRV vaccine strains have failed to protect many swine herds against PR. Herein, we developed a self-assembled nanoparticle vaccine that induces potent protective immunity against PRV infection. PRV glycoprotein D (gD) was expressed using the baculovirus expression system and further presented on the lumazine synthase (LS) 60-meric protein scaffolds via the SpyTag003/SpyCatcher003 covalent coupling system. In mouse and piglet models, LSgD nanoparticles emulsified with the ISA 201VG adjuvant elicited robust humoral and cellular immune responses. Furthermore, LSgD nanoparticles provided effective protection against PRV infection and eliminated pathological symptoms in the brain and lungs. Collectively, the gD-based nanoparticle vaccine design appears to be a promising candidate for potent protection against PRV infection.

Genomic Characterization and gE/gI-Deleted Strain Construction of Novel PRV Variants Isolated in Central China

Pseudorabies virus (PRV) variants have caused substantial economic losses in the swine industry in China since 2011. To surveil the genetic variation in PRV field strains, here, two novel variant strains of PRV were isolated from Shanxi Province in central China and were designated SX1910 and SX1911. To identify the genetic characteristics of the two isolates, their complete genomes were sequenced, and phylogenetic analysis and sequence alignment revealed that field PRV variants have undergone genetic variations; notably, the protein-coding sequences UL5, UL36, US1 and IE180 exhibited extensive variation and contained one or more hypervariable regions. Furthermore, we also found that the glycoproteins gB and gD of the two isolates had some novel amino acid (aa) mutations. Importantly, most of these mutations were located on the surface of the protein molecule, according to protein structure model analysis. We constructed a mutant virus of SX1911 with deletion of the gE and gI genes via CRISPR/Cas9. When tested in mice, SX1911-ΔgE/gI-vaccinated mice were protected within a comparable range to Bartha-K61-vaccinated mice. Additionally, a higher dose of inactivated Bartha-K61 protected the mice from lethal SX1911 challenge, while a lower neutralization titer, higher viral load and more severe microscopic lesions were displayed in Bartha-K61-vaccinated mice. These findings highlight the need for continuous monitoring of PRV and novel vaccine development or vaccination program design for PRV control in China.

Characterization of Pseudorabies Virus Associated with Severe Respiratory and Neuronal Signs in Old Pigs

Pseudorabies virus (PRV) represents a leading threat to the global pig industry. Generally, pigs exhibit a pronounced age resistance against PRV, and the virus generally does not cause severe clinical signs and even death in old pigs. However, we characterized two PRV strains (HeN21 and HuB20) associated with severe respiratory and neuronal signs in old pigs. Among these two strains, HeN21 was isolated from the tonsil of a 24-week-old pig that died from severe neuronal and respiratory signs in a PRV-outbreak farm where a commercial PRV attenuated vaccine developed based on a PRV variant was used; while, HuB20 was isolated from the lung and lymph node of a 20-week-old with symptoms in another farm where Bartha-K61 vaccine was used. In vitro evaluations in different cell models demonstrated that HeN21 and HuB20 led to similar cytotoxic effects to those caused by PRV variants on PK-15, Vero, and SK-N-SH cells after 30 hours of inoculation. However, HeN21 possessed a higher titer than the other PRV variants from the first to the fifth passage on PK-15 cells and induced plaques with larger size. In vivo assessments in mouse and fattening pig models showed that inoculations of HeN21 and HuB20 caused higher morbidity and mortality and severe pathological damages in tested animals. In particular, challenge of HeN21 led to severe respiratory and neuronal signs in 90-day-old pigs. These two strains displayed higher virus loads on the main organs of challenged mice and pigs. Phylogenetic analysis revealed that HeN21 and HuB20 belonged to genotype II. In addition, recombinant events were identified in the genomes of HeN21 and HuB20, and several events were located within genes associated with PRV virulence. Our data herein may suggest the emergence of novel PRV strains in China.

Recombinant Pseudorabies Virus Usage in Vaccine Development against Swine Infectious Disease

Pseudorabies virus (PRV) is the pathogen of pseudorabies (PR), which belongs to the alpha herpesvirus subfamily with a double stranded DNA genome encoding approximately 70 proteins. PRV has many non-essential regions for replication, has a strong capacity to accommodate foreign genes, and more areas for genetic modification. PRV is an ideal vaccine vector, and multivalent live virus-vectored vaccines can be developed using the gene-deleted PRV. The immune system continues to be stimulated by the gene-deleted PRVs and maintain a long immunity lasting more than 4 months. Here, we provide a brief overview of the biology of PRV, recombinant PRV construction methodology, the technology platform for efficiently constructing recombinant PRV, and the applications of recombinant PRV in vaccine development. This review summarizes the latest information on PRV usage in vaccine development against swine infectious diseases, and it offers novel perspectives for advancing preventive medicine through vaccinology.

Napyradiomycin A4 and Its Relate Compounds, a New Anti-PRV Agent and Their Antibacterial Activities, from Streptomyces kebangsaanensis WS-68302

Two new napyradiomycins derivatives, napyradiomycin A4 (1) and A80915 H (2), along with five known ones, were isolated from the ethyl acetate extract of fermentation culture of Streptomyces kebangsaanensis WS-68302. Their structures were elucidated by extensive spectroscopic analysis, including HR-MS, 1D and 2D NMR, CD spectrum, as well as comparison with literature data. Compound 1 exhibited significant antiviral activity against PRV (Pseudorabies virus) with an IC₅₀ value of 2.056 μM and therapeutic ratio at 14.98, suggesting that it might have potential for development of an antiviral agent. Moreover, compound 1 displayed the strongest inhibition against PRV protein among the tested napyradiomycins in the indirect immunofuorescence assay. Compounds 3 and 4 showed higher activities against swine pathogenic Streptococcus suis than the positive control penicillin G sodium salt, with MIC values of 3.125 and 6.25 μg/mL, respectively. Compounds 1 and 3-6 exhibited moderate antibacterial activity against the swine pathogenic Erysipelothrix rhusiopathiae, with MIC values ranging from 25 to 50 μg/mL.

Cytopathic and Genomic Characteristics of a Human-Originated Pseudorabies Virus

Pseudorabies virus (PRV) generally infects pigs and threatens the pig industry. However, recently we have isolated a PRV strain designated hSD-1/2019 from infected humans. In this study, we compared the complete genome sequence of hSD-1/2019 with those of pig-originated PRV strains. Sequence alignments revealed that the genome sequence of hSD-1/2019 was highly homologous to those of the porcine PRV strains. Phylogenetic analyses found that hSD-1/2019 was the closest related to porcine PRV endemic strains in China, particularly the variant strains circulating recently. We also showed that the glycoproteins important for the multiplication and pathogenesis of hSD-1/2019 were highly similar to those of the pig endemic strains. Diversifying selection analyses revealed that hSD-1/2019 and pig variant strains are under diversifying selection. Recombination analysis indicated that hSD-1/2019 was a recombinant of several PRV variant strains and an earlier PRV classic strain. Finally, we found that both human and pig-originated PRV strains could induce cytopathic effects in cells from humans, pigs, and mice, but only the human PRV and pig-variant PRV formed large syncytia in human cell lines. The data presented in this study contribute to our understanding of the molecular basis for the pathogenesis of human PRV from a genomic aspect.

Progress on innate immune evasion and live attenuated vaccine of pseudorabies virus

Pseudorabies virus (PRV) is a highly infectious disease that can infect most mammals, with pigs as the only natural host, has caused considerable economic losses to the pig husbandry of the world. Innate immunity is the first defense line of the host against the attack of pathogens and is essential for the proper establishment of adaptive immunity. The host uses the innate immune response to against the invasion of PRV; however PRV makes use of various strategies to inhibit the innate immunity to promote the virus replication. Currently, live attenuated vaccine is used to prevent pig from infection with the PRV worldwide, such as Bartha K61. However, a growing number of data indicates that these vaccines do not provide complete protection against new PRV variants that have emerged since late 2011. Here we summarized the interactions between PRV and host innate immunity and the current status of live attenuated PRV vaccines to promote the development of novel and more effective PRV vaccines.

Comprehensive evaluation of the safety and immunogenicity of a gene-deleted variant pseudorabies virus attenuated vaccine

Pseudorabies virus (PRV) variant infections have caused a substantial economic impact on swine production in the absence of new powerful candidate vaccines. In this study, we developed and evaluated a gene-deleted variant pseudorabies virus (PRV)-attenuated vaccine, PRV GX-ΔTK/IES, in which the genes TK, gI, gE, US9 and US2 were deleted. During a study of innocuousness, all mice inoculated with PRV GX-ΔTK/IES survived, neither clinical signs nor pathological changes were observed, and viral genomes could not be detected in the blood and tissues. All piglets inoculated with high titres of PRV GX-ΔTK/IES remained clinically healthy, and neither fever nor clinical signs were observed. Viral detection results were negative in nasal swab samples, blood and tissue samples. Moreover, none of the cohabitated piglets seroconverted during a trial on horizontal transmission. The immunogenicity was assessed through a vaccination and challenge experiment in piglets. Piglets vaccinated with PRV GX-ΔTK/IES and the commercial vaccine were completely protected from subsequent PRV infection, and the level of immunity and protection induced by PRV GX-ΔTK/IES was better than that provided by the live commercial vaccine. Thus, PRV GX-ΔTK/IES is completely safe for both nontarget and target animals and can be regarded as a novel live gene-deleted PRV vaccine candidate.

The Immune Efficacy of Inactivated Pseudorabies Vaccine Prepared from FJ-2012ΔgE/gI Strain

An emerging pseudorabies virus (PRV) variant has been reported on Bartha-K61-vaccinated farms since 2011, causing great economic losses to China's swine-feeding industry. In this study, two vaccines, FJ-2012ΔgE/gI-GEL02 and FJ-2012ΔgE/gI-206VG, were administered to piglets for immune efficacy investigation. Humoral immunity response, clinical signs, survival rate, tissue viral load, and pathology were assessed in piglets. The results showed that both vaccines were effective against the PRV FJ-2012 challenge, the piglets all survived while developing a high level of gB-specific antibody and neutralizing antibody, the virus load in tissue was alleviated, and no clinical PR signs or pathological lesions were displayed. In the unimmunized challenged group, typical clinical signs of pseudorabies were observed, and the piglets all died at 7 days post-challenge. Compared with commercial vaccines, the Bartha-K61 vaccine group could not provide full protection, which might be due to a lower vaccine dose; the inactivated vaccine vPRV* group piglets survived, displaying mild clinical signs. The asterisk denotes inactivation. These results indicate that FJ-2012ΔgE/gI-GEL02 and FJ-2012ΔgE/gI-206VG were effective and could be promising vaccines to control or eradicate the new PRV epidemic in China.

The Inactivated gE/TK Gene-Deleted Vaccine Against Pseudorabies Virus Type II Confers Effective Protection in Mice and Pigs

The highly virulent and antigenic variant of Pseudorabies virus (PRV) that emerged from classical Bartha-K61-vaccinated pig herds has caused substantial economic losses to the swine industry in China since 2011. A safe and more effective vaccine is most desirable. In this study, a gE/TK gene-deficient PRV, namely, HD/c, was constructed based on a PRV type II DX strain isolated from a commercial vaccine-immunized farm and the HD/c-based inactivated vaccine was formulated and evaluated for its safety, immunogenicity, and protective efficacy in mice and piglets. The resulting PRV HD/c strain has a similar growth curve to the parental DX strain. After vaccination, the inactivated HD/c vaccine did not cause any visible gross pathological or histopathological changes in the tissues of mice and piglets and provided rapid and potent protection against the challenge of the classical and variant PRVs at day 21 post-vaccination in mice. A single immunization of 10^8.5TCID₅₀ inactivated PRV HD/c strain-elicited robust immunity with high titer of neutralizing antibody and provided complete protection from the lethal challenge of PRV DX strain in piglets. These results indicated that the inactivated PRV HD/c vaccine with the deletion of gE/TK genes was a safe and effective PRV vaccine candidate for the control of PRV.

Alphaherpesvirus glycoprotein E: A review of its interactions with other proteins of the virus and its application in vaccinology

The viral envelope glycoprotein E (gE) is required for cell-to-cell transmission, anterograde and retrograde neurotransmission, and immune evasion of alphaherpesviruses. gE can also interact with other proteins of the virus and perform various functions in the virus life cycle. In addition, the gE gene is often the target gene for the construction of gene-deleted attenuated marker vaccines. In recent years, new progress has been made in the research and vaccine application of gE with other proteins of the virus. This article reviews the structure of gE, the relationship between gE and other proteins of the virus, and the application of gE in vaccinology, which provides useful information for further research on gE.

Pseudorabies Virus: From Pathogenesis to Prevention Strategies

Pseudorabies (PR), also called Aujeszky’s disease (AD), is a highly infectious viral disease which is caused by pseudorabies virus (PRV). It has been nearly 200 years since the first PR case occurred. Currently, the virus can infect human beings and various mammals, including pigs, sheep, dogs, rabbits, rodents, cattle and cats, and among them, pigs are the only natural host of PRV infection. PRV is characterized by reproductive failure in pregnant sows, nervous disorders in newborn piglets, and respiratory distress in growing pigs, resulting in serious economic losses to the pig industry worldwide. Due to the extensive application of the attenuated vaccine containing the Bartha-K61 strain, PR was well controlled. With the variation of PRV strain, PR re-emerged and rapidly spread in some countries, especially China. Although researchers have been committed to the design of diagnostic methods and the development of vaccines in recent years, PR is still an important infectious disease and is widely prevalent in the global pig industry. In this review, we introduce the structural composition and life cycle of PRV virions and then discuss the latest findings on PRV pathogenesis, following the molecular characteristic of PRV and the summary of existing diagnosis methods. Subsequently, we also focus on the latest clinical progress in the prevention and control of PRV infection via the development of vaccines, traditional herbal medicines and novel small RNAs. Lastly, we provide an outlook on PRV eradication.

Same Dosages of rPRV/XJ5-gI−/gE−/TK− Prototype Vaccine or Bartha-K61 Vaccine Similarly Protects Growing Pigs Against Lethal Challenge of Emerging vPRV/XJ-5 Strain

Variant pseudorabies viruses (vPRV) have constantly emerged in China since late 2011. In the present study, a 1 × 10^6.0 TCID₅₀ per-animal dosage of a commercially available Bartha-K61 vaccine and an rPRV/XJ5-gI⁻/gE⁻/TK⁻ prototype vaccine freshly extracted from the vPRV/XJ-5 at the same dose were administered to evaluate the immune effectiveness thereof on growing pigs to prevent lethal strikes caused by vPRV/XJ-5. The results suggest that the Bartha-K61 vaccine at a dose of 1 × 10^6.0 TCID₅₀ per animal and the same dosage of the rPRV/XJ5-gI⁻/gE⁻/TK⁻ prototype vaccine protected growing pigs against the lethal challenge of vPRV/XJ-5 strain with 100% survive rate. Furthermore, the outcome of the clinical score, virus shedding, weight gain, and viral loads in different pig tissues in these two groups demonstrates that either the Bartha-K61 vaccine or the rPRV/XJ5-gI⁻/gE⁻/TK⁻ prototype vaccine at the same dose exhibited parallel efficacy in pigs against the lethal challenge with the XJ-5 strain of vPRV.

The Epidemiology and Variation in Pseudorabies Virus: A Continuing Challenge to Pigs and Humans

Pseudorabies virus (PRV) can infect most mammals and is well known for causing substantial economic losses in the pig industry. In addition to pigs, PRV infection usually leads to severe itching, central nervous system dysfunction, and 100% mortality in its non-natural hosts. It should be noted that increasing human cases of PRV infection have been reported in China since 2017, and these patients have generally suffered from nervous system damage and even death. Here, we reviewed the current prevalence and variation in PRV worldwide as well as the PRV-caused infections in animals and humans, and briefly summarized the vaccines and diagnostic methods used for pseudorabies control. Most countries, including China, have control programs in place for pseudorabies in domestic pigs, and thus, the disease is on the decline; however, PRV is still globally epizootic and an important pathogen for pigs. In countries where pseudorabies in domestic pigs have already been eliminated, the risk of PRV transmission by infected wild animals should be estimated and prevented. As a member of the alphaherpesviruses, PRV showed protein-coding variation that was relatively higher than that of herpes simplex virus-1 (HSV-1) and varicella-zoster virus (VZV), and its evolution was mainly contributed to by the frequent recombination observed between different genotypes or within the clade. Recombination events have promoted the generation of new variants, such as the variant strains resulting in the outbreak of pseudorabies in pigs in China, 2011. There have been 25 cases of PRV infections in humans reported in China since 2017, and they were considered to be infected by PRV variant strains. Although PRV infections have been sporadically reported in humans, their causal association remains to be determined. This review provided the latest epidemiological information on PRV for the better understanding, prevention, and treatment of pseudorabies.

Bartha-K61 vaccine protects nursery pigs against challenge with novel european and asian strains of suid herpesvirus 1

The present study investigates the pathogenicity of two recently isolated strains of Suid herpesvirus 1 (SuHV1), the Greek strain Hercules and the Chinese strain HeN1, in unvaccinated pigs and in pigs vaccinated with a Bartha-K61 strain. In an experiment performed in negative pressure kiosks (isolators), 45-day old seronegative pigs previously oronasally /intramuscularly vaccinated with the Bartha-K61 vaccine strain, along with unvaccinated controls, were challenged either with the Hercules strain or the HeN1 strain of SuHV1. All animals were observed daily for clinical signs and body temperature and nasal swabs, faeces, blood and bodyweight were collected up to a maximum period of 20 days post-challenge (dpc). The results showed that, in the unvaccinated pigs, HeN1 strain was more virulent than the Hercules strain, with increased mortality, shorter time to death and higher group clinical score (p < 0.05). However, after vaccination with the Bartha-K61 vaccine, there was a drastic reduction in morbidity, mortality, bodyweight loss and virus excretion to almost a similar extent in both strains (p < 0.05). No significant differences were seen among the pigs of the two vaccinated groups compared to unvaccinated unchallenged controls, except a slight elevation in body temperature and in clinical score in the HeN1 vaccinees at 2 and 3 dpc, while bodyweight gain was similar to that of the negative control pigs. Our study showed that despite differences in virulence, the standard vaccination scheme with the Bartha-K61 strain could equally protect nursery pigs against both the European and Chinese strains.

Design of live-attenuated animal vaccines based on pseudorabies virus platform

Pseudorabies virus (PRV) is a double-stranded DNA virus with a genome approximating 150 kb in size. PRV contains many non-essential genes that can be replaced with genes encoding heterogenous antigens without affecting viral propagation. With the ability to induce cellular, humoral and mucosal immune responses in the host, PRV is considered to be an ideal and potential live vector for generation of animal vaccines. In this review, we summarize the advances in attenuated recombinant PRVs and design of PRV-based live vaccines as well as the challenge of vaccine application.

A Review of Pseudorabies Virus Variants: Genomics, Vaccination, Transmission, and Zoonotic Potential

Pseudorabies virus (PRV), the causative agent of Aujeszky’s disease, has a broad host range including most mammals and avian species. In 2011, a PRV variant emerged in many Bartha K61-vaccinated pig herds in China and has attracted more and more attention due to its serious threat to domestic and wild animals, and even human beings. The PRV variant has been spreading in China for more than 10 years, and considerable research progresses about its molecular biology, pathogenesis, transmission, and host–virus interactions have been made. This review is mainly organized into four sections including outbreak and genomic evolution characteristics of PRV variants, progresses of PRV variant vaccine development, the pathogenicity and transmission of PRV variants among different species of animals, and the zoonotic potential of PRV variants. Considering PRV has caused a huge economic loss of animals and is a potential threat to public health, it is necessary to extensively explore the mechanisms involved in its replication, pathogenesis, and transmission in order to ultimately eradicate it in China.

The Construction and Immunogenicity Analyses of Recombinant Pseudorabies Virus With NADC30-Like Porcine Reproductive and Respiratory Syndrome Virus-Like Particles Co-expression

Porcine reproductive and respiratory syndrome (PRRS) and pseudorabies (PR) are highly infectious swine diseases and cause significant financial loss in China. The respiratory system and reproductive system are the main target systems. Previous studies showed that the existing PR virus (PRV) and PRRS virus (PRRSV) commercial vaccines could not provide complete protection against PRV variant strains and NADC30-like PRRSV strains in China. In this study, the PRV variant strain XJ and NADC30-like PRRSV strain CHSCDJY-2019 are used as the parent for constructing a recombinant pseudorabies virus (rPRV)-NC56 with gE/gI/TK gene deletion and co-expressing NADC30-like PRRSV GP5 and M protein. The rPRV-NC56 proliferated stably in BHK-21 cells, and it could stably express GP5 and M protein. Due to the introduction of the self-cleaving 2A peptide, GP5 and M protein were able to express independently and form virus-like particles (VLPs) of PRRSV in rPRV-NC56-infected BHK-21 cells. The rPRV-NC56 is safe for use in mice; it can colonize and express the target protein in mouse lungs for a long time. Vaccination with rPRV-NC56 induces PRV and NADC30-like PRRSV specific humoral and cellular immune responses in mice, and protects 100% of mice from virulent PRV XJ strain. Furthermore, the virus-neutralizing antibody (VNA) elicited by rPRV-NC56 showed significantly lower titer against SCNJ-2016 (HP-PRRSV) than that against CHSCDJY-2019 (NADC30-like PRRSV). Thus, rPRV-NC56 appears to be a promising candidate vaccine against NADC30-like PRRSV and PRV for the control and eradication of the variant PRV and NADC30-like PRRSV.

A noval strategy of deletion in PK gene for construction of a vaccine candidate with exellent safety and complete protection efficiency against high virulent Chinese pseudorabies virus variant

A variant of pseudorabies virus (PRV) with enhanced pathogenicity have emerged in many vaccinated swine herds in China since 2011. PRV^ΔTK&gE-AH02, a previously described TK/gE deletion PRV strain arising from the PRV variant AH02LA, has been shown to be safe for PRV antibody positive piglets, and could provide protection against emerging PRV variants. However, inoculation of PRV^ΔTK&gE-AH02 into PRV antibody negative neonatal piglets caused lethal infection. In the study, in order to attenuate the virulence of PRV^ΔTK&gE-AH02, an additional deletion of 1ཞ13bp of US3 (the serine/threonine kinase, PK) gene was performed to generate a TK/PK/gE deletion PRV variant (PRV^{ΔTK&PK&gE-AH02}). We found that the growth kinetics of PRV^{ΔTK&PK&gE-AH02} was similar to that of PRV^ΔTK&gE-AH02. Mice inoculated with PRV^{ΔTK&PK&gE-AH02} in different dose (10^4.0∼10^7.0 TCID₅₀) survived and showed no observable clinical symptoms. No virus was detected in the brain or lung of the mice inoculated with PRV^{ΔTK&PK&gE-AH02}. Moreover, mice inoculated with PRV^{ΔTK&PK&gE-AH02} and PRV^ΔTK&gE-AH02 showed similar survival against virulent PRV AH02LA strain. Importantly, safety test showed no clinical symptoms in PRV antibody negative neonatal piglets that were intranasally inoculated with PRV^{ΔTK&PK&gE-AH02} at a dose of 10^6.5 TCID₅₀, indicating that the virulence of PRV^{ΔTK&PK&gE-AH02} was significantly mitigated. Piglets immunized with PRV^{ΔTK&PK&gE-AH02} exhibited a high serum neutralization index. All piglets inoculated intramuscularly (I.M.) with 1 mL (10^5.0 TCID₅₀) PRV^{ΔTK&PK&gE-AH02} were completely protected against challenge intranasally (I.N.) with 2LD₅₀ (10^6.5TCID₅₀) PRV AH02LA strain. In summary, our results indicate that deletion of 1ཞ13bp of US3 (PK) can provide a useful way for further attenuation of PRV and the PRV^{ΔTK&PK&gE-AH02} might be a promising vaccine candidate for controlling of the virulent PRV variants in China.

A natural product, (S)-10-Hydroxycamptothecin inhibits pseudorabies virus proliferation through DNA damage dependent antiviral innate immunity

Pseudorabies virus (PRV), a member of the subfamily alphaherpesvirinae, is one of the most important pathogenes that cause acute death in infected pigs and leads to substantial economic losses in the global swine industry. Recently, China's emerging PRV mutant strains resulted in the traditionally commercial vaccines not providing complete protection. Some studies reported that PRV could infect humans and cause endophthalmitis and encephalitis under certain circumstances. It is necessary to develop alternative manners to control the virus infection. Here, by screening a library of natural products, (S)-10-Hydroxycamptothecin (10-HCPT) was revealed to inhibit PRV replication with a selective index of 270.04. And 10-HCPT inhibited PRV replication by blocking the viral genome replication but not inhibiting the viral attachment, internalization, and release. RNA interference assay showed that 10-HCPT inhibited PRV replication by targeting DNA topoisomerase 1 (TOP1). Meanwhile, 10-HCPT treatment induced DNA damage response and stimulated antiviral innate immunity. Animal challenge experiments showed that 10-HCPT effectively alleviated clinical signs and hispathology, and increased INF-β responses in lung and brain tissues of mice induced by PRV infection. The results demonstrate that 10-HCPT is a promising therapeutic agent to control PRV infection.

Construction and Immunogenicity of a Recombinant Pseudorabies Virus Variant With TK/gI/gE/11k/28k Deletion

In China, the re-emerging pseudorabies virus (PRV) variant has caused large-scale outbreaks of pseudorabies in swine herds with classical PRV vaccine immunization since late 2011. Here, a recombinant PRV with TK/gI/gE/11k/28k deletion was constructed based on variant HN1201 strain isolated in 2012, by the bacterial artificial chromosome infectious clones. Compared with the parental virus, the recombinant PRV rHN1201^{TK−/gE−/gI−/11k−/28k−} showed a similar virus grown curve and exhibited smaller plaques. The vaccination of rHN1201^{TK−/gE−/gI−/11k−/28k−} could elicit an earlier and higher level of gB antibody, and the neutralizing antibodies elicited by rHN1201^{TK−/gE−/gI−/11k−/28k−} were effective against both PRV classical and variant strains. Clinically, the body temperature of the pigs immunized with rHN1201^{TK−/gE−/gI−/11k−/28k−} was significantly lower than that of the classical PRV vaccine immunized pigs, and the recombinant PRV could provide effective protection against the challenge with the PRV variant. These results imply that the rHN1201^{TK−/gE−/gI−/11k−/28k−} could be a promising vaccine candidate for the prevention of the current epidemic of pseudorabies in China.

Construction of a quadruple gene-deleted vaccine confers complete protective immunity against emerging PRV variant challenge in piglets

Background

Pseudorabies virus (PRV) causes Aujeszky’s disease or pseudorabies (PR) in pigs worldwide, which leads to heavy economic losses to the swine industry. Pigs are the natural host, meanwhile, animals such as dogs, cats, foxes, rabbits, cattle and sheep are susceptible to infection. In 2011, the emerging PRV variant led to the outbreak of PR in Bartha-K61 vaccinated pigs. The PR outbreaks demonstrated that the Bartha-K61 vaccine did not provide full protection against the emerging PRV variant. It is widely believed that PRV live attenuated vaccine could control PRV infection.

Methods

In this study, we developed a novel PRV live attenuated vaccine by deleting its gI, gE, US9, and US2 genes through CRISPR/Cas9, which was named PRV GDFS-delgI/gE/US9/US2.

Results

Safety experiments confirmed that PRV GDFS-delgI/gE/US9/US2 was safe for 5- to 7-day-old suckling piglets. Piglets immunized with the PRV GDFS-delgI/gE/US9/US2 vaccine did not produce PRV gE-specific antibodies but could generate PRV gB-specific antibodies and high neutralizing titers against the PRV GDFS strain (variant PRV strain) or PRV Ea strain (older PRV strain). After challenge with the emerging PRV GDFS variant, none of the piglets immunized with the PRV GDFS-delgI/gE/US9/US2 vaccine showed any clinical signs, and their rectal temperatures were normal. Moreover, the autopsy and histopathological analyses revealed that the piglets in the PRV GDFS-delgI/gE/US9/US2 vaccine group did not show apparent gross or pathological lesions. Furthermore, the piglets in the PRV GDFS-delgI/gE/US9/US2 vaccine groups did not present weight loss. According to the criteria of the OIE terrestrial manual, the results of the experiment confirmed that the PRV GDFS-delgI/gE/US9/US2 vaccine could provide full protection against the emerging PRV variant strain in piglets.

Conclusions

The PRV GDFS-delgI/gE/US9/US2 strain is a potential new live attenuated vaccine against emerging PRV variant strain infections in China.

Isolation and Phylogenetic Analysis of Reemerging Pseudorabies Virus Within Pig Populations in Central China During 2012 to 2019

To understand the biological characteristics of the reemerging pseudorabies virus (PRV) strains, a total of 392 tissue samples were collected from diseased pigs during reemerging PR outbreaks between 2012 and 2019 on farms in central China where swine had been immunized with Bartha-K61 and 51 (13. 01%) were positive for the gE gene by PCR. Sixteen PRV strains were isolated and caused clinical symptoms and death in mice. Subsequently, gE, gC, gB, and gD complete genes were amplified from the 16 PRV isolates and sequenced. Phylogenetic analysis based on these four gene sequences shows that the 16 PRV isolates were more closely related to the Chinese PRV variants (after 2012) but genetically differed from early Chinese PRV isolates (before 2012). Sequence analysis reveals that PRV isolates exhibited amino acid insertions, substitutions, or deletions compared with early Chinese PRV isolates and European–American PRV strains. In addition, this is the first report that eight isolates (8/16) in this study harbor a unique amino acid substitution at position 280 (F to L) of the gC protein, and six isolates have an amino acid substitution at position 338 (A to V) of the gD protein compared with the Chinese PRV variants. The emulsion containing inactivated PRV NY isolate could provide complete protection against the NY isolate. This study might enrich our understanding of the evolution of reemerging PRV strains as well as pave the way for finding a model virus to develop a novel vaccine based on reemerging PRV strains.

Tandem Mass Tag-Based Quantitative Proteomic Analysis of ISG15 Knockout PK15 Cells in Pseudorabies Virus Infection

Pseudorabies virus (PRV) is recognized as one of the most important pathogens of swine and poses a serious threat to the swine industry worldwide. Available commercial vaccines fail to protect against the emergence of new PRV strains. Therefore, the new protein targets against PRV highlight the urgent need for uncovering the molecular determinants of host cellular proteins following PRV infection. Interferon-stimulated gene 15 (ISG15) demonstrates an outstanding antiviral response. However, the molecular mechanism of ISG15 that affects PRV replication is incompletely known. Here, we performed a tandem mass tag (TMT)-based approach to quantitatively identify protein expression changes in PRV-infected ISG15 knockout PK15 (ISG15^−/−-PK15) cells. In total, 4958 proteins were identified by using TMT coupled with LC-MS/MS in this study. In the PRV- and mock-infected groups, 241 differentially expressed proteins (DEPs) were identified, 162 upregulated and 79 downregulated proteins at 24 h post-infection (hpi), among which AFP, Vtn, Hsp40, Herc5, and Mccc1 may play important roles in PRV propagation. To ensure the validity and reliability of the proteomics data, the randomly selected DEPs were verified by RT-qPCR and Western blot analysis, and the results were consistent with the TMT results. Bioinformatics analyses further demonstrated that the DEPs are mainly involved in various biological processes and signaling pathways, such as signal transduction, the digestive system, and the PI3K-AKT pathway. These findings may provide new insight into molecular mechanisms for PRV infection, which is helpful for identifying potential protein targets for antiviral agents.

Whole-Genome Sequence Analysis of Pseudorabies Virus Clinical Isolates from Pigs in China between 2012 and 2017 in China

Pseudorabies virus (PRV) is an economically significant swine infectious agent. A PRV outbreak took place in China in 2011 with novel virulent variants. Although the association of viral genomic variability with pathogenicity is not fully confirmed, the knowledge concerning PRV genomic diversity and evolution is still limited. Here, we sequenced 54 genomes of novel PRV variants isolated in China from 2012 to 2017. Phylogenetic analysis revealed that China strains and US/Europe strains were classified into two separate genotypes. PRV strains isolated from 2012 to 2017 in China are highly related to each other and genetically close to classic China strains such as Ea, Fa, and SC. RDP analysis revealed 23 recombination events within novel PRV variants, indicating that recombination contributes significantly to the viral evolution. The selection pressure analysis indicated that most ORFs were under evolutionary constraint, and 19 amino acid residue sites in 15 ORFs were identified under positive selection. Additionally, 37 unique mutations were identified in 19 ORFs, which distinguish the novel variants from classic strains. Overall, our study suggested that novel PRV variants might evolve from classical PRV strains through point mutation and recombination mechanisms.

Pathogenicity and immunogenicity of a gI/gE/TK/UL13-gene-deleted variant pseudorabies virus strain in swine

Pseudorabies is a highly infectious disease with severe clinical symptoms, causing acute death in infected pigs and leading to substantial economic losses among swine producers. In this study, a vaccine candidate strain in which the protein kinase UL13 gene was deleted was constructed with the CRISPR/Cas9 system based on the recombinant pseudorabies virus (PRV) ZJ01-ΔgI/gE/TK. Pigs immunized with ZJ01-ΔgI/gE/TK or ZJ01-ΔgI/gE/TK/UL13 produced high levels of anti-gB antibodies and virus-neutralizing antibodies. ZJ01-ΔgI/gE/TK/UL13 provided greater protective efficacy against challenge with PRV variant strain ZJ01 than did Bartha-K61 or ZJ01-ΔgI/gE/TK. The pigs vaccinated with ZJ01-ΔgI/gE/TK/UL13 excreted significantly less virus than those vaccinated with Bartha-K61 or ZJ01-ΔgI/gE/TK. The viral loads in the lungs of pigs treated with ZJ01-ΔgI/gE/TK/UL13 were lower than those in pigs treated with ZJ01-ΔgI/gE/TK after challenge with PRV variant strain ZJ01. These data indicated that ZJ01-ΔgI/gE/TK/UL13 had greater protective efficacy and safety than the commercial ZJ01-ΔgI/gE/TK and Bartha-K61 vaccines, and could be developed as a promising vaccine candidate for the prevention and control of this disease.

Ghonaim A, Wu H, Sun Q, Fan S, He Q. Recombinant Pseudorabies Virus with TK/gE Gene Deletion and Flt3L Co-Expression Enhances the Innate and Adaptive Immune Response via Activating Dendritic Cells

Owing to viral evolution and recombination, emerging pseudorabies virus (PRV) strains have caused unprecedented outbreaks in swine farms even when the pigs were previously vaccinated, which might indicate that traditional vaccines were unable to provide effective protection. The development of safe and efficacious vaccines presents prospects to minimize the clinical signs and eventually eradicate the infection. In this study, we used an emerging PRV strain, HNX, as the parental strain to construct a recombinant PRV with TK/gE gene deletion and Fms-related tyrosine kinase 3 ligand (Flt3L) expression, named HNX-TK⁻/gE⁻-Flt3L. HNX-TK⁻/gE⁻-Flt3L enhanced the maturation of bone marrow derived dendritic cells (DCs) in vitro. Significantly more activated DCs were detected in HNX-TK⁻/gE⁻-Flt3L-immunized mice compared with those immunized with HNX-TK⁻/gE⁻. Subsequently, a remarkable increase of neutralizing antibodies, gB-specific IgG antibodies, and interferon-gamma (IFN-γ) was observed in mice vaccinated with HNX-TK⁻/gE⁻-Flt3L. In addition, a lower mortality and less histopathological damage were observed in HNX-TK⁻/gE⁻-Flt3L vaccinated mice with upon PRV lethal challenge infection. Taken together, our results revealed the potential of Flt3L as an ideal adjuvant that can activate DCs and enhance protective immune responses and support the further evaluation of HNX-TK⁻/gE⁻-Flt3L as a promising PRV vaccine candidate.

Recombinant pseudorabies virus with gI/gE deletion generated by overlapping polymerase chain reaction and homologous recombination technology induces protection against the PRV variant PRV-GD2013

BACKGROUND

Since 2011, numerous highly virulent and antigenic variant viral strains have been reported in pigs that were vaccinated against the swine pseudorabies virus. These infections have led to substantial economic losses in the Chinese swine industry.

RESULTS

This study, constructed a novel recombinant vaccine strain with gI/gE deletion (PRV-GD2013-ΔgI/gE) by overlapping PCR and homologous recombination technology. The growth curves and plaque morphology of the recombinant virus were similar to those of the parental strain. However, PRV-GD2013-ΔgI/gE infection was significantly attenuated in mice compared with that of PRV-GD2013. Two-week-old piglets had normal rectal temperatures and displayed no clinical symptoms after being inoculated with 105 TCID50 PRV-GD2013-ΔgI/gE, indicating that the recombinant virus was avirulent in piglets. Piglets were immunized with different doses of PRV-GD2013-ΔgI/gE, or a single dose of Bartha-K61 or DMEM, and infected with PRV-GD2013 at 14 days post-vaccination. Piglets given high doses of PRV-GD2013-ΔgI/gE showed no obvious clinical symptoms, and their antibody levels were higher than those of other groups, indicating that the piglets were completely protected from PRV-GD2013.

CONCLUSIONS

The PRV-GD2013-ΔgI/gE vaccine strain could be effective for immunizing Chinese swine herds against the pseudorabies virus (PRV) strain.

Current Status and Challenge of Pseudorabies Virus Infection in China

Pseudorabies (PR), also called Aujeszky’s disease, is a highly infectious disease caused by pseudorabies virus (PRV). Without specific host tropism, PRV can infect a wide variety of mammals, including pig, sheep, cattle, etc., thereby causing severe clinical symptoms and acute death. PRV was firstly reported in China in 1950s, while outbreaks of emerging PRV variants have been documented in partial regions since 2011, leading to significant economic losses in swine industry. Although scientists have been devoting to the design of diagnostic approaches and the development of vaccines during the past years, PR remains a vital infectious disease widely prevalent in Chinese pig industry. Especially, its potential threat to human health has also attracted the worldwide attention. In this review, we will provide a summary of current understanding of PRV in China, mainly focusing on PRV history, the existing diagnosis methods, PRV prevalence in pig population and other susceptible mammals, molecular characteristics, and the available vaccines against its infection. Additionally, promising agents including traditional Chinese herbal medicines and novel inhibitors that may be employed to treat this viral infection, are also discussed.

Adefovir dipivoxil efficiently inhibits the proliferation of pseudorabies virus in vitro and in vivo

Since 2011, highly pathogenic pseudorabies virus (PRV) variants that emerged on many farms in China have posed major economic burdens to the animal industry and have even recently caused several human cases of viral encephalitis. Currently, there are no approved effective drugs to treat PRV associated diseases in humans or pigs. Thus, it is important to develop a new effective drug for the treatment of PRV infection. To this end, we established a novel rapid method to screen drugs against PRV from 1818 kinds of small molecular drugs approved by the FDA. Using this method, we identified 21 kinds of them that can strongly suppress the proliferation of PRV. Mitoxantrone, puromycin dihydrochloride, mitoxantrone hydrochloride and adefovir dipivoxil effectively inhibited PRV in vitro. Of them, only adefovir dipivoxil could potently protect mice against lethal PRV infection. Our work identifies several kinds of potential therapeutics against PRV and may offer important guidance for controlling PRV epidemics and treating associated diseases in humans and animals.

Isolation and Characterization of a Variant Psedorabies Virus HNXY and Construction of rHNXY-∆TK/∆gE

The outbreak of pseudorabies in China, caused by more virulent pseudorabies virus (PRV) than the classical strains, has led to considerable economic losses. In this study, PRV strain HNXY was isolated from the Henan province of China in 2015 from the pig farm with severe reproductive failure in sows and a high mortality in piglets. The 50% tissue culture infectious doses (TCID50) of HNXY in Vero cells were examined to be 106.5/mL, and the neutralisation titer against Bartha-K61 was significantly higher than against HNXY when tested with the serum from Bartha-K61 vaccinated pigs. The 50% lethal doses (LD50) of HNXY to six-week-old BALB/c mice and two-month-old PRV-free pigs were both 102.3 TCID50. HNXY was classified as genotype II, and numerous amino acid variations were found in gB, gE, gC, gD, TK, and RR1 proteins, compared with PRV from other countries or those prevalent in China before 2012. The attenuated rHNXY-∆TK/∆gE was further constructed, which presented significantly smaller plaques than HNXY, as well as the similar growth kinetics. rHNXY-∆TK/∆gE was confirmed to be non-pathogenic to six-week-old BALB/c mice and zero-day-old piglets. This study isolated updated PRV promising to develop into a new vaccine candidate.

A single dose glycoprotein D-based subunit vaccine against pseudorabies virus infection

Pseudorabies Virus (PRV) is the causative agent of Pseudorabies (PR), also known as Aujeszky's Disease, one of the most important infectious diseases in swine, resulting in huge economic losses to the swine industry globally. The emergence of mutant PRV strains after 2011 resulted in a sharp decrease in the efficacy of available commercial vaccines. To develop a more effective vaccine that can prevent the spread of PRV, glycoprotein B (gB), glycoprotein C (gC) and glycoprotein D (gD) from recent PRV isolates were expressed in a baculovirus system and their protective efficacy was tested in mice and piglets. Neutralizing antibody titers (NAs) in mice vaccinated with gB, gC and gD peaked at 28 days after immunization and then slowly declined. NAs in the mice immunized with gD were remarkably higher than other groups. After a lethal challenge of 5 LD₅₀ with mutant PRV-HNLH strain, the survival rates of gB and gD were 100% and 87.5% respectively, which was significantly higher than gC group (50%). Piglets vaccinated with the gD and gB + D vaccines developed the highest NAs 7 days post immunization. No piglets in these two groups exhibited clinical symptoms, high body temperature or virus shedding following challenge with 10^6.6 TCID₅₀ with the mutant PRV-HNLH strain. Histopathology and immunohistochemistry showed remarkably reduced pathological damage and viral loads in gD and gB + D groups. Furthermore, the duration of the NAs induced by gD vaccine could maintain as long as four months after a single dose. The current study indicates that a gD-based vaccine could be developed for the efficient control of PRV.

Pseudorabies virus infection inhibits stress granules formation via dephosphorylating eIF2α

Pseudorabies virus (PRV) is one of the most notorious pathogens in the global pig industry. During infection, viruses may evolve various strategies, such as modulating stress granules (SGs) formation, to create an optimal surroundings for viral replication. However, the interplay between PRV infection and SGs formation remains largely unknown. Here we showed that PRV infection markedly blocked SGs formation induced by sodium arsenate (AS) and DL-Dithiothreitol (DTT). Accordantly, the phosphorylation of eIF2α was markedly inhibited in PRV-infected cells, although two eIF2α kinases double-stranded RNA-activated protein kinase (PKR) and PKR-like ER kinase (PERK) were activated during PRV infection. Furthermore, we also found that the dephosphorylation of eIF2α occurred at the early stage of virus infection but without the elevated production of GADD34 and PP1. Moreover, inhibition of PP1 activity by salubrinal could counteract PRV-mediated eIF2α dephosphorylation partially and inhibit virus replication. Our results revealed that, on the one hand, PRV infection activated eIF2α kinases PKR (latter inhibited) and PERK, and on the other hand, PRV encoded-functions dephosphorylated eIF2α and inhibited SGs formation to facilitate virus replication.

Construction and immunogenicity of a gE/gI/TK-deleted PRV based on porcine pseudorabies virus variant

Pseudorabies (PR) caused by re-emerging pseudorabies virus (PRV) variant has outbroken among PRV vaccine-immunized swine herds on many Chinese pig farms, with severe socioeconomic consequences since late 2011. Here, a gE/gI/TK-deleted recombinant virus (rPRV NY-gE^-/gI^-/TK^-) was constructed based on PRV NY strain from 2012 through homologous DNA recombination and gene-editing technology termed clustered regularly interspaced palindromic repeats (CRISPR)/associated (Cas9) system. The rPRV NY-gE^-/gI^-/TK^- strain showed similar growth kinetics to the parental PRV NY strain in vitro, and was safe for mice. Sixty mice were injected subcutaneously (s.c.) twice with 10^6.0 TCID₅₀ of rPRV NY-gE^-/gI^-/TK^- and DMEM, respectively, with two-week interval. The levels of PRV gB antibodies and neutralizing antibodies against PRV NY in mice immunized with rPRV NY-gE^-/gI^-/TK^- were higher than those in the DMEM control group. The number of T lymphocyte subclasses CD3⁺, CD4⁺ and CD8⁺ in rPRV NY-gE^-/gI^-/TK^--immunized mice was higher than that in DMEM-injected mice. After challenge with 10^6.0 TCID₅₀ PRV NY at 42 dpi, all rPRV NY-gE^-/gI^-/TK^--immunized mice survived without exhibiting any pathological lesions in different tissues and intranuclear eosinophilic inclusions of the brain, and the viral genomic copy numbers in various organs of mice were obviously lower than DMEM group. These results showed the rPRV NY-gE^-/gI^-/TK^- could be a promising next-generation vaccine to control now epidemic PR in China.

Functional analysis of prv-miR-LLT11a encoded by pseudorabies virus

Viral-encoded microRNAs (miRNAs) have vital roles in the regulation of virus replications and host immune responses. The results of previous studies have indicated that miRNA clusters are involved in the replication and virulence of the pseudorabies virus (PRV), which may potentially lead to immune escape or facilitation of PRV replication. This study's previous research revealed that prv-miR-LLT11a was differentially expressed during PRV infection. The present study's results have demonstrated that prv-miR-LLT11a could significantly inhibit PRV replication. It was further determined that SLA-1 was the target gene of prv-miR-LLT11a, and simultaneously, that overexpression of prv-miR-LLT11a could downregulate the mRNA and protein levels of SLA-1 in a dose-independent manner. Furthermore, the present study also observed that prv-miR-LLT11a can downregulate TAP1 expression. Our findings provide a better understanding of the molecular mechanism involved in the effects of prv-miR-LLT11a on SLA-1 and TAP1 as well as its involvement in immune system evasion of PRV.

Glycoproteins C and D of PRV Strain HB1201 Contribute Individually to the Escape From Bartha-K61 Vaccine-Induced Immunity

The newly emerged pseudorabies virus (PRV) novel variants can escape from the immunity induced by the classical vaccine Bartha-K61. Here we investigated the underlying mechanisms by constructing chimeric mutants between epidemic strain HB1201 and the Bartha-K61 vaccine. Our analyses focused on three viral envelope glycoproteins, namely gB, gC, and gD, as they exhibit remarkable genetic variations and are also involved in induction of protective immunity. The corresponding genes were swapped reciprocally either individually or in combination by using CRISPR/Cas9 technology and homologous recombination. The rescued chimeric viruses exhibited differential sensitivity to neutralizing antibodies in vitro, and gC was found to be the major contributor to inefficient neutralization against HB1201 by anti-Bartha-K61 serum. When tested in the 4-week-piglet model, substitution with HB1201 gC enabled Bartha-K61 to induce a protective immunity against HB1201 at a high challenge dose of 10⁷ TCID₅₀. Interestingly, despite a relatively lower cross-neutralization ability, the gD exchange also enabled Bartha-K61 to protect piglets from lethal challenge. In both cases, clinical signs and microscopic lesions were eased, and so was the viral tissue load with the exception of brain. A better protection could be achieved when both gC and gD were swapped in terms of reducing viral load in brain and virus-induced microscopic lesions. Thus, our studies not only revealed individual roles of gC and gD variations in the immune escape and also suggested a synergistic effect of both proteins on induction of protective immunity. These findings have important implications in novel vaccine development for PRV control in China.

Genome Characteristics and Evolution of Pseudorabies Virus Strains in Eastern China from 2017 to 2019

Since late 2011, outbreaks of pseudorabies virus (PRV) have occurred in southern China causing major economic losses to the pig industry. We previously reported that variant PRV forms and recombination in China could be the source of continued epidemics. Here, we analyzed samples from intensive pig farms in eastern China between 2017 and 2019, and sequenced the main glycoproteins (gB, gC, gD, and gE) to study the evolution characteristics of PRV. Based on the gC gene, we found that PRV variants belong to clade 2 and detected a founder effect during by the PRV epidemic. In addition, we detected inter- and intra-clade recombination; in particular, inter-clade recombination in the gB genes of strains FJ-ZXF and FJ-W2, which were recombinant with clade 1 strains. We also found specific amino-acid changes and positively selected sites, possibly associated with functional changes. This analysis of the emergence of PRV in China illustrates the need for continuous monitoring and the development of vaccines against specific variants of PRV.