Histopathology of brain functional areas in pigs infected by porcine pseudorabies virus

Fermented Erigeron breviscapus flavonoids: anti-pseudorabies virus efficacy and mechanisms in vitro and in vivo

Introduction

Erigeron breviscapus exhibits anti-inflammatory properties, protects neuronal cells and enhances immune function. Modern traditional Chinese medicine fermentation techniques can increase the bioactive compound content in Erigeron breviscapus. However, its potential therapeutic effects against the porcine pseudorabies virus (PRV) remain unclear.

Methods

A PRV infection model was established in mouse trigeminal ganglion (TG) cells to determine the optimal antiviral mode of action of flavonoids from fermented Erigeron breviscapus (FEBF). Additionally, a PRV-infected rat model was developed to evaluate the in vivo antiviral efficacy of FEBF.

Results

FEBF demonstrated a higher protective rate and a lower viral copy number compared to unfermented E. breviscapus flavonoids (EBF). The protective effect was most pronounced under toxicological and inhibitory conditions, surpassing the blocking effect. PRV infection upregulated TLR4, MyD88, and NF-κB p65 protein expression during the pre-infection phase, followed by their downregulation after 12 h. FEBF regulated PRV-induced changes in protein expression, restoring them to near-normal levels by 36 h. In vivo assessments of pathological injury, PRV viral load, neuronal count, and neuronal apoptosis indicated that FEBF provided superior neuroprotection compared to both Minocycline (MINO), a broad-spectrum neuroprotective drug, and unfermented EBF. Mechanistic studies further revealed that FEBF modulated microglial polarization and regulated the inflammatory cytokines IL-6, TNF-α, IL-4, and IL-10.

Conclusion

These findings demonstrate that FEBF exhibits significant antiviral effects against PRV in both in vitro and in vivo models. FEBF represents a promising candidate for the development of anti-PRV therapeutics.

Characteristics of the pseudorabies virus strain GDWS2 with severe neurological signs and high viral shedding capacity in pigs

Pseudorabies virus (PRV) poses a serious threat to the global swine industry, as PRV infection can lead to reproductive disorders in sows and high mortality in newborn piglets. Although pigs typically exhibit age-related resistance to PRV, with older pigs exhibiting milder symptoms upon infection, the recent isolation of multiple highly pathogenic PRV variants and reports of severe symptoms and even death in older pigs have garnered much attention. The GDWS2 strain isolated in this study exhibits characteristics similar to those of highly pathogenic strains. GDWS2 was isolated from the brain tissue of a 90-day-old diseased pig that exhibited severe respiratory and neurological symptoms. The pig originated from a farm that had been previously vaccinated with the Bartha-k61 strain. In vitro experiments demonstrated that GDWS2 induces substantial cytopathic effects in PK-15, VERO, BHK cells, and PAM. Moreover, GDWS2 formed larger plaques and exhibited higher early replication titers in PK-15 cells compared to the highly pathogenic variant strain JM isolated in China. Phylogenetic analysis revealed that GDWS2 belongs to PRV genotype II, with gD, gE, and TK genes showing high homology to those of highly pathogenic PRV variants. Additionally, GDWS2 harbors unique insertions or mutations in the US1, UL36, and UL5 gene regions, and its genome contains recombination events with PRV variants, Bartha, or genotype I strains. In vivo experiments further confirmed the high pathogenicity of GDWS2. In rabbit and 90-day-old pig models, GDWS2, compared with the JM strain, caused high mortality rates, accompanied by severe pathological damage. Notably, in the 90-day-old pig model, the GDWS2 challenge group exhibited more severe respiratory and neurological symptoms, and enhanced neurotropism and shedding capacity. The data from this study may indicate the emergence of a naturally recombined and highly pathogenic PRV variant in China once again.

Astrocyte-derived MMP-9 is a key mediator of pseudorabies virus penetration of the blood-brain barrier and tight junction disruption

Pseudorabies virus (PRV) infection leads to viral encephalitis and neurological damage in mice, causing significant neurological symptoms and brain damage. This study aimed to investigate the cellular mechanisms of PRV-induced encephalopathy and the role of matrix metalloproteinase-9 (MMP-9) in blood-brain barrier (BBB) disruption. We found that PRV infection increased the number of astrocytes and induced a phenotypic shift from the A2 to the A1 subtype, which was associated with increased secretion of MMP-9. MMP-9 was identified as a critical mediator of PRV-induced BBB disruption, as it degrades collagen VI, leading to BBB damage. PRV was shown to penetrate the BBB via a paracellular pathway, and MMP-9 deletion reversed this damage, mitigating tight junction injury. Additionally, PRV infection caused an "inflammatory storm" in the central nervous system (CNS), with increased levels of the chemokines CCL-3, CCL-4, and CCL-5; the cytokines IL-6 and IL-18; and TNF-α. The expression of INF-γ was significantly decreased. In conclusion, PRV infection disrupts the BBB and induces an inflammatory response in the CNS, with MMP-9 playing a key role in mediating BBB damage. These findings provide insights into the pathogenesis of PRV-induced encephalopathy and potential therapeutic targets for viral encephalitis.

Immunosuppression of the Nasal Cavity by a Novel Pathogenic Pseudorabies Virus Isolation from Cattle in China

The respiratory mucosa serves as a primary entry point for numerous pathogenic microbes, and the respiratory mucosa secretes type I and III interferons (IFNs), the first generation of antiviral cytokines, in response to viral infection. The pseudorabies virus (PRV) causes serious illnesses in many domestic and wild animal species, particularly in pigs and cattle. However, more information is needed about the immunosuppressive properties and evolutionary history of emerging PRV field strains in China's respiratory system. The PRV field strain JS2022, which was obtained from a cow farm for this investigation, is a spontaneous recombination of early PRV variant strains in the Jiangsu region and is similar to the PRV variations recovered in China in terms of its entire genome sequence. According to sequence analysis, JS2022 has a spontaneous deletion of 1,212 bp in the gE gene, 502 bp in the gI gene, and 192 bp in the glycoprotein (g) C gene. Pathogenicity analysis revealed that intranasal JS2022 causes severe neurological symptoms in calves, but this effect is different from that of ZJ01. In addition, a considerable number of viral antigens in the nasal mucosa were detected by immunohistochemical staining. Therefore, we constructed a bovine nasal mucosal explant model that maintained good cell morphology and activity even after 5 days. In bovine nasal mucosal explants, JS2022 and ZJ01 can cause infection, and the viral load increases dramatically over time. Quantitative research revealed that 24 hr after infection, JS2022 dramatically reduced the expression of downstream interferon-stimulated genes and the innate immune factors IFN-β and IFN-λ3 and bovine nasal mucosal explants. Overall, our results highlight the significance of PRV surveillance in cattle and offer a resource for learning more about the clinical traits and development of PRV.

Resveratrol alleviated neuroinflammation induced by pseudorabies virus infection through regulating microglial M1/M2 polarization

BACKGROUND

Pseudorabies virus (PRV) infections in susceptible non-porcine species trigger uncontrolled inflammations and eventually fatal encephalitis. Resveratrol (Res) has broad pharmacological functions including anti-virus, anti-inflammation, and neuroprotective.

PURPOSE

We attempted to investigate the potential of Res in ameliorating PRV infection pathology in mice and decipher the mechanism of Res in treating PRV.

METHODS

The mice were infected by PRV to investigate the protective effect of Res. Blood-brain barrier (BBB) permeability, H&E/Nissl/TUNEL staining, Real-time PCR and ELISA analyses were performed. Primary microglia and neuron were isolated from mice and cultured. The co-culture model of microglia and neuron was established by transwell. Immunofluorescence assay and flow cytometry were used.

RESULTS

In this study, we showed that Res ameliorated brain damage by reducing BBB permeability in PRV-infected mice, and diminished the expressions of MMP-2, MMP-9 and ZO-1 in the cortex. Pathological changes of neurons by H&E/Nissl/TUNEL staining suggested that Res could alleviate neuronal lesions. Moreover, Res inhibited the expressions of pro-inflammatory factors (IL-6, TNF-α) and chemokines (CCL3, CXCL10, MCP-1), but increased the expressions of anti-inflammatory factors (IL-4, IL-10) and neurotrophic factor (TGF-β, NGF and GDNF) in brain. In vitro cultured microglia cells, Res could suppress M1 microglia polarization and activate M2 microglia polarization. Co-culture of PRV-infected microglia with neuron cells by transwell system indicated that Res alleviated inflammatory response and neuronal apoptosis.

CONCLUSION

This study provided evidence that Res could protect mice from PRV-induced encephalitis through regulation of microglia polarization and neuronal apoptosis suggesting the potential for treatment of viral encephalitis.

Microscopic lesions and modulation of gene expression in cervical medulla during BoAHV-1and BoAHV-5 infection: A mini-review

Bovine herpesvirus (BoAHV) types 1 and 5 are closely-related neurotropic alpha-herpesviruses. BoAHV-1 generally causes respiratory and genital disease but can occasionally cause encephalitis. BoAHV-5 is the causative agent of non suppurative meningoencephalitis in calves. During neuroinvasion, both viruses reach the central and peripheral nervous system. While brain alterations are well-described, the changes that occur in the medulla have not been fully detailed. In this work, we integrated and analyzed the virological findings, the microscopic lesions and the changes that occur in the expression of genes related to the innate immunity, cell cycle and apoptosis in the cervical medulla of calves experimentally-infected with BoAHV-1 and BoAHV-5. This will contribute to the understanding of the differential neuropathogenesis of these alpha-herpesviruses of cattle.

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.

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.