Pathogenesis of porcine reproductive and respiratory syndrome virus

Stability of five strains of PRRSV in tap water at different temperatures

Porcine reproductive and respiratory syndrome (PRRS) is considered one of the most economically important diseases of swine, as outbreaks in the U.S. continue occurring despite current rigorous biosecurity measures. Limited information is available regarding the possibility of water contamination and the role of this milieu in dissemination of the PRRS virus. In this study, the survivability of the PRRSV in tap water at three temperatures (4°C, 21-23°C, and 37°C) was assessed. Tap water obtained from a laboratory faucet underwent different treatments involving autoclaving and dechlorination. Four strains of PRRSV-2 (L1A 1-7-4, L1C 1-4-4 SD, L9 1-4-2, L5 2-5-2) and one of PRRSV-1 (Lelystad), grown in the MARC-145 cell line with titers ranging from 4.0 to 5.5 log10 TCID50/0.1 mL, were added to the water samples followed by incubation at different temperatures. At various times, the samples were removed and titrated in cell cultures to determine the amount of viable virus. While there were no major differences between virus strains and water treatments, results showed a statistically significant (p < 0.01) prolonged survivability at lower temperatures: all strains remained viable for over 28 days at 4°C, 3-7 days at 21-23°C, and more than 24 hour sat 37°C. The time required for a 99% decrease in virus titer (T99) further confirmed its longer survivability at lower temperatures, and the comparisons among these results indicate a potential risk of drinking tap water as a PRRSV carrier in farms, especially at lower temperatures.

Evaluation of the utility of testicular-only processing fluid for porcine reproductive and respiratory syndrome virus diagnostics and the effect of sample pooling on the test results

Introduction

The testicular-only processing fluid (TOPF) obtained from piglet testicles after castration could be an alternative sample for porcine reproductive and respiratory syndrome (PRRS) laboratory diagnosis. If this matrix were proved useful, testing it would spare piglets the stress of blood drawing and eliminate some labour required to take blood samples. The aim of the study was to evaluate the utility of TOPF for this diagnostic purpose.

Material and Methods

Serum-and-TOPF pairs from male piglets and sera from female piglets were tested using commercial ELISA and real-time RT-PCR kits. For the pooling simulation, 10 μL aliquots of TOPF separated into low-, moderately and highly positive were mixed with appropriate volumes of negative TOPF samples. This simulated pools of 5, 10, 20, 40 and 80 samples containing 1 positive for serological analyses and pools of 10, 20, 40, 80, 160 and 320 samples containing 1 positive in molecular analyses.

Results

The percentages of anti-porcine reproductive and respiratory syndrome virus (PRRSV) antibodies were statistically significantly different (P-value < 0.05) between boar sera (69.55%) and TOPF (54.49%), as well as between gilt sera (74.52%) and TOPF. However, after adjusting the cut-off value, no significant differences were noted. The RNA of PRRSV was detected in 21.26% of male sera, 15.23% of TOPFs and 17.00% of female sera. Pooled sample testing revealed discrepancies in positive results associated with the pool size and original sample positivity strength.

Conclusion

TOPF samples can be a valuable matrix for laboratory PRRS diagnosis in piglets. However, it is important to be aware of the potential for false-negative results.

Research Progress on the GP3 Protein of Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious immunosuppressive disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV) that is characterized by a highly variable gene sequence and a high rate of recombination, thereby contributing to difficulties in the clinical prevention and control of this virus. Glycosylated protein 3 (GP3) is the most glycosylated protein in PRRSV, and is closely associated with the composition of PRRSV virus particles, infection, and immune evasion. This review summarizes the structural features, genetic evolutionary patterns, glycosylation of GP3 and its interactions with other PRRSV and host proteins, associations with PRRSV infection and virulence, and immunomodulatory roles. Additionally, it provides an overview of research progress on monoclonal antibodies and vaccines targeting GP3. This study aims to provide a theoretical foundation for better understanding the structure and function of GP3, of the mechanisms of PRRSV infection, and the development of novel vaccines.

Molecular mechanism of autophagy in porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome virus (PRRSV), a significant pathogen affecting the swine industry globally, has been shown to manipulate host cell processes, including autophagy, to facilitate its replication and survival within the host. Autophagy, an intracellular degradation process crucial for maintaining cellular homeostasis, can be hijacked by viruses for their own benefit. During PRRSV infection, autophagy plays a complex role, both as a defense mechanism of the host and as a tool exploited by the virus. This review explores the current understanding of the molecular mechanisms underlying autophagy induction under PRRSV infection, its impact on virus replication, and the potential implications for viral pathogenesis and antiviral strategies. By synthesizing the latest research findings, this article aims to enhance our understanding of the intricate relationship between autophagy and PRRSV, paving the way for novel therapeutic approaches against this swine pathogen.

PRRSV hijacks DDX3X protein and induces ferroptosis to facilitate viral replication

Porcine reproductive and respiratory syndrome virus (PRRSV) is a severe disease with substantial economic consequences for the swine industry. The DEAD-box helicase 3 (DDX3X) is an RNA helicase that plays a crucial role in regulating RNA metabolism, immunological response, and even RNA virus infection. However, it is unclear whether it contributes to PRRSV infection. Recent studies have found that the expression of DDX3X considerably increases in Marc-145 cells when infected with live PRRSV strains Ch-1R and SD16; however, it was observed that inactivated viruses did not lead to any changes. By using the RK-33 inhibitor or DDX3X-specific siRNAs to reduce DDX3X expression, there was a significant decrease in the production of PRRSV progenies. In contrast, the overexpression of DDX3X in host cells substantially increased the proliferation of PRRSV. A combination of transcriptomics and metabolomics investigations revealed that in PRRSV-infected cells, DDX3X gene silencing severely affected biological processes such as ferroptosis, the FoxO signalling pathway, and glutathione metabolism. The subsequent transmission electron microscopy (TEM) imaging displayed the typical ferroptosis features in PRRSV-infected cells, such as mitochondrial shrinkage, reduction or disappearance of mitochondrial cristae, and cytoplasmic membrane rupture. Conversely, the mitochondrial morphology was unchanged in DDX3X-inhibited cells. Furthermore, silencing of the DDX3X gene changed the expression of ferroptosis-related genes and inhibited the virus proliferation, while the drug-induced ferroptosis inversely promoted PRRSV replication. In summary, these results present an updated perspective of how PRRSV infection uses DDX3X for self-replication, potentially leading to ferroptosis via various mechanisms that promote PRRSV replication.

Genetic variation and recombination analysis of the GP5 gene of the porcine reproductive and respiratory syndrome virus in Thailand

Introduction

Porcine reproductive and respiratory syndrome (PRRS) is a significant threat to the global swine industry, and its prevalence in Thailand spans over two decades.

Methods

To understand the genetic variation and recombination of the PRRS virus (PRRSV) GP5 gene in Thailand, we retrieved 726 GP5 gene sequences from the NCBI database. Phylogenetic trees were constructed using the neighbor-joining (NJ) and maximum likelihood (ML) methods, and recombination analysis was performed.

Results

Homology analysis was conducted on 83 PRRSV-1 and 83 PRRSV-2 strains. Phylogenetic analysis revealed the prevalence of both PRRSV-1 and PRRSV-2 strains in Thailand, with the latter exhibiting wider distribution. PRRSV-1 strains clustered into clades A, D, and H, while PRRSV-2 strains grouped into lineages 1, 5, and sublineage 8.7, further divided into 8.7/HP and 8.7/NA sublineages. Sublineage 8.7/NA strains accounted for a significant proportion of circulating PRRSV-2 strains. Homology analysis showed nucleotide and amino acid similarities ranging from 75.4 to 100.0% and 41.3 to 100.0% for PRRSV-1, and 78.6 to 100.0% and 70.8 to 100.0% for PRRSV-2 strains. Amino acid sequence alignments revealed mutations, insertions, and deletions in PRRSV-1 GP5, and key residue mutations in PRRSV-2 GP5 associated with biological functions. Recombination analysis identified two recombination events within PRRSV-2 sublineage 8.7 strains.

Discussion

These findings confirm the variability of the GP5 protein. This study enhances our understanding of PRRSV prevalence and genetic variation in Thailand, contributing valuable insights for PRRS prevention and control.

MiR-320 inhibits PRRSV replication by targeting PRRSV ORF6 and porcine CEBPB

Porcine reproductive and respiratory syndrome (PRRS), a highly contagious disease caused by Porcine reproductive and respiratory syndrome virus (PRRSV), results in huge economic losses to the world pig industry. MiRNAs have been reported to be involved in regulation of viral infection. In our study, miR-320 was one of 21 common differentially expressed miRNAs of Meishan, Pietrain, and Landrace pig breeds at 9-h post-infection (hpi). Bioinformatics and experiments found that PRRSV replication was inhibited by miR-320 through directly targeting PRRSV ORF6. In addition, the expression of CCAAT enhancer binding protein beta (CEBPB) was also inhibited by miR-320 by targeting the 3' UTR of CEBPB, which significantly promotes PRRSV replication. Intramuscular injection of pEGFP-N1-miR-320 verified that miR-320 significantly inhibited the replication of PRRSV and alleviated the symptoms caused by PRRSV in piglets. Taken together, miR-320 have significant roles in the infection and may be promising therapeutic target for PRRS.

Research progress on the N protein of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV exhibits genetic diversity and complexity in terms of immune responses, posing challenges for eradication. The nucleocapsid (N) protein of PRRSV, an alkaline phosphoprotein, is important for various biological functions. This review summarizes the structural characteristics, genetic evolution, impact on PRRSV replication and virulence, interactions between viral and host proteins, modulation of host immunity, detection techniques targeting the N protein, and progress in vaccine development. The discussion provides a theoretical foundation for understanding the pathogenic mechanisms underlying PRRSV virulence, developing diagnostic techniques, and designing effective vaccines.

Characterizing the detection of inactivated Mycoplasma hyopneumoniae DNA in the respiratory tract of pigs

A positive Mycoplasma hyopneumoniae PCR result in a clinical specimen may eventually represent the mere detection of non-viable bacteria, complicating the diagnostic interpretation. Thus, the objective of this study was to evaluate the PCR detection of non-viable M. hyopneumoniae and its residual cell-free DNA in live pigs. Pigs were inoculated with either active or inactivated M. hyopneumoniae and were sampled for up to 14 days. Mycoplasma hyopneumoniae was not detected by PCR at any timepoint in pigs inoculated with the inactivated bacterium, suggesting that in healthy pigs, the non-viable M. hyopneumoniae DNA was rapidly sensed and cleared.

Survival of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) in the Environment

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important diseases of swine, with losses due to poor reproductive performance and high piglet and growing pig mortality. Transmission of porcine reproductive and respiratory syndrome virus (PRRSV) may occur by both direct and indirect routes; the latter includes exposure to PRRSV-contaminated fomites, aerosols, and arthropod vectors. This review has collected available data on the ex-vivo environmental stability and persistence of PRRSV in an effort to highlight important sources of the virus and to determine the role of environmental conditions on the stability of the virus, especially temperature. The ex-vivo settings include fomites (solid, porous, and liquid fomites), insects, people, and pork meat, as well as the role of environmental conditions on the stability of the virus, especially temperature.

Integrative transcriptomic profiling of mRNA, miRNA, circRNA, and lncRNA in alveolar macrophages isolated from PRRSV-infected porcine

Introduction

The porcine reproductive and respiratory syndrome virus (PRRSV) continues to pose a significant threat to the global swine industry, attributed largely to its immunosuppressive properties and the chronic nature of its infection. The absence of effective vaccines and therapeutics amplifies the urgency to deepen our comprehension of PRRSV's intricate pathogenic mechanisms. Previous transcriptomic studies, although informative, are partially constrained by their predominant reliance on in vitro models or lack of long-term infections. Moreover, the role of circular RNAs (circRNAs) during PRRSV invasion is yet to be elucidated.

Methods

In this study, we employed an in vivo approach, exposing piglets to a PRRSV challenge over varied durations of 3, 7, or 21 days. Subsequently, porcine alveolar macrophages were isolated for a comprehensive transcriptomic investigation, examining the expression patterns of mRNAs, miRNAs, circRNAs, and long non-coding RNAs (lncRNAs).

Results

Differentially expressed RNAs from all four categories were identified, underscoring the dynamic interplay among these RNA species during PRRSV infection. Functional enrichment analyses indicate that these differentially expressed RNAs, as well as their target genes, play a pivotal role in immune related pathways. For the first time, we integrated circRNAs into the lncRNA-miRNA-mRNA relationship, constructing a competitive endogenous RNA (ceRNA) network. Our findings highlight the immune-related genes, CTLA4 and SAMHD1, as well as their associated miRNAs, lncRNAs, and circRNAs, suggesting potential therapeutic targets for PRRS. Importantly, we corroborated the expression patterns of selected RNAs through RT-qPCR, ensuring consistency with our transcriptomic sequencing data.

Discussion

This study sheds lights on the intricate RNA interplay during PRRSV infection and provides a solid foundation for future therapeutic strategizing.

Porcine reproductive and respiratory syndrome virus regulates lipid droplet accumulation in lipid metabolic pathways to promote viral replication

Porcine reproductive and respiratory syndrome (PRRS) is a severe respiratory disease caused by porcine reproductive and respiratory syndrome virus (PRRSV) that can lead to the abortion of pregnant sows and decreased boar semen quality. However, the mechanisms of PRRSV replication in the host have not yet been fully elucidated. As lipid metabolism and lipid droplets (LDs) have been reported to play important roles in the replication of various viruses, we aimed to explore the mechanisms through which LDs affect PRRSV replication. Laser confocal and transmission electron microscopy revealed that PRRSV infection promoted intracellular LD accumulation, which was significantly reduced by treatment with the NF-κB signaling pathway inhibitors BAY11-7082 and metformin hydrochloride (MH). In addition, treatment with a DGAT1 inhibitor significantly reduced the protein expression of Phosphorylated NF-ΚB P65and PIκB and the transcription of IL-1β and IL-8 in the NF-κB signaling pathway. Furthermore, we showed that the reduction of the NF-κB signaling pathway and LDs significantly reduced PRRSV replication. Together, the findings of this study suggest a novel mechanism through which PRRSV regulates the NF-κB signaling pathway to increase LD accumulation and promote viral replication. Moreover, we demonstrated that both BAY11-7082 and MH can reduce PRRSV replication by reducing the NF-κB signaling pathway and LD accumulation. This study lays a theoretical foundation for research on the mechanism of PRRS prevention and control, as well as the research and development of antiviral drugs.

Discovery of Brassica Yellows Virus and Porcine Reproductive and Respiratory Syndrome Virus in Diaphorina citri and Changes in Virome Due to Infection with 'Ca. L. asiaticus'

Detection of new viruses or new virus hosts is essential for the protection of economically important agroecosystems and human health. Increasingly, metatranscriptomic data are being used to facilitate this process. Such data were obtained from adult Asian citrus psyllids (ACP) (Diaphorina citri Kuwayama) that fed solely on mandarin (Citrus ×aurantium L.) plants grafted with buds infected with 'Candidatus Liberibacter asiaticus' (CLas), a phloem-limited bacterium associated with the severe Asian variant of huanglongbing (HLB), the most destructive disease of citrus. Brassica yellows virus (BrYV), the causative agent of yellowing or leafroll symptoms in brassicaceous plants, and its associated RNA (named as BrYVaRNA) were detected in ACP. In addition, the porcine reproductive and respiratory syndrome virus (PRRSV), which affects pigs and is economically important to pig production, was also found in ACP. These viruses were not detected in insects feeding on plants grafted with CLas-free buds. Changes in the concentrations of insect-specific viruses within the psyllid were caused by coinfection with CLas. IMPORTANCE The cross transmission of pathogenic viruses between different farming systems or plant communities is a major threat to plants and animals and, potentially, human health. The use of metagenomics is an effective approach to discover viruses and vectors. Here, we collected buds from the CLas-infected and CLas-free mandarin (Citrus ×aurantium L. [Rutaceae: Aurantioideae: Aurantieae]) trees from a commercial orchard and grafted them onto CLas-free mandarin plants under laboratory conditions. Through metatranscriptome sequencing, we first identified the Asian citrus psyllids feeding on plants grafted with CLas-infected buds carried the plant pathogen, brassica yellows virus and its associated RNA, and the swine pathogen, porcine reproductive and respiratory syndrome virus. These discoveries indicate that both viruses can be transmitted by grafting and acquired by ACP from CLas+ mandarin seedlings.

Antibody-dependent enhancement of porcine reproductive and respiratory syndrome virus infection downregulates the levels of interferon-gamma/lambdas in porcine alveolar macrophages in vitro

Fc gamma receptor-mediated antibody-dependent enhancement (ADE) can promote virus invasion of target cells, sometimes exacerbating the severity of the disease. ADE may be an enormous hurdle to developing efficacious vaccines for certain human and animal viruses. ADE of porcine reproductive and respiratory syndrome virus (PRRSV) infection has been demonstrated in vivo and in vitro. However, the effect of PRRSV-ADE infection on the natural antiviral immunity of the host cells is yet to be well investigated. Specifically, whether the ADE of PRRSV infection affects the levels of type II (interferon-gamma, IFN-γ) and III (interferon-lambdas, IFN-λs) interferons (IFNs) remains unclear. In this study, our results showed that PRRSV significantly induced the secretion of IFN-γ, IFN-λ1, IFN-λ3, and IFN-λ4 in porcine alveolar macrophages (PAMs) in early infection, and weakly inhibited the production of IFN-γ, IFN-λ1, IFN-λ3, and IFN-λ4 in PAMs in late infection. Simultaneously, PRRSV infection significantly increased the transcription of interferon-stimulated gene 15 (ISG15), ISG56, and 2′, 5′-oligoadenylate synthetase 2 (OAS2) in PAMs. In addition, our results showed that PRRSV infection in PAMs via the ADE pathway not only significantly decreased the synthesis of IFN-γ, IFN-λ1, IFN-λ3, and IFN-λ4 but also significantly enhanced the generation of transforming growth factor-beta1 (TGF-β1). Our results also showed that the ADE of PRRSV infection significantly reduced the mRNAs of ISG15, ISG56, and OAS2 in PAMs. In conclusion, our studies indicated that PRRSV-ADE infection suppressed innate antiviral response by downregulating the levels of type II and III IFNs, hence facilitating viral replication in PAMs in vitro. The ADE mechanism demonstrated in the present study furthered our understanding of persistent pathogenesis following PRRSV infection mediated by antibodies.

Effects of a water-soluble formulation of tylvalosin on disease caused by porcine reproductive and respiratory syndrome virus alone in sows or in combination with Mycoplasma hyopneumoniae in piglets

BACKGROUND

The effect of a water-soluble formulation of tylvalosin (Aivlosin® 625 mg/g granules) on disease caused by porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae (Mhyop) was investigated in two animal studies. In a PRRSV challenge model in pregnant sows (n = 18), six sows received water medicated at target dose of 5 mg tylvalosin/kg body weight/day from 3 days prior to challenge until the end of gestation. Six sows were left untreated, with a third group remaining untreated and unchallenged. Sows were challenged with PRRSV-2 at approximately 85 days of gestation. Cytokines, viremia, viral shedding, sow reproductive parameters and piglet performance to weaning were evaluated. In a dual infection study (n = 16), piglets were challenged with Mhyop on days 0, 1 and 2, and with PRRSV-1 on day 14 and euthanized on day 24. From day 10 to 20, eight piglets received water medicated at target dose of 20 mg tylvalosin/kg body weight/day and eight piglets were left untreated. Cytokines, viremia, bacteriology and lung lesions were evaluated.

RESULTS

In the PRRSV challenge study in pregnant sows, tylvalosin significantly reduced the levels of serum IL-8 (P < 0.001), IL-12 (P = 0.032), TNFα (P < 0.001) and GM-CSF (P = 0.001). IL-8 (P = 0.100) tended to be lower in uterus of tylvalosin sows. All piglets from tylvalosin sows surviving to weaning were PRRSV negative in faecal swabs at weaning compared to 33.3% PRRSV positive piglets from untreated sows (P = 0.08). In the dual challenge study in piglet, tylvalosin reduced serum IL1β, IL-4, IL-6, IL-8, IL-10, IL-12, IL-1α, IL-13, IL-17A, IL-18, GM-CSF, TGFβ1, TNFα, CCL3L1, MIG, PEPCAM-1 (P < 0.001) and increased serum IFNα, IL-1ra and MIP-1b (P < 0.001). In the lungs, tylvalosin reduced IL-8, IL-10 and IL-12 compared to untreated pigs (P < 0.001) and tended to reduce TNFα (P = 0.082). Lung lavage samples from all tylvalosin treated piglets were negative for Mhyop (0 cfu/mL) compared to the untreated piglets which had mean Mhyop counts of 2.68 × 10⁴ cfu/mL (P = 0.023).

CONCLUSION

Overall, tylvalosin reduced both local and systemic proinflammatory cytokines after challenge with respiratory pathogens in sows and in piglets. Tylvalosin was effective in reducing Mhyop recovery from the lungs and may reduce virus shedding in piglets following transplacental PRRSV infection in sows.

Evaluation of Intradermal PRRSV MLV Vaccination of Suckling Piglets on Health and Performance Parameters under Field Conditions

Porcine reproductive and respiratory syndrome virus (PRRSV) causes respiratory disease in weaning and growing pigs. A vaccination against PRRSV is one of the most important control measures. This trial aimed to evaluate the effect of the intradermal (ID) administration of a PRRSV-1 modified live virus (MLV) vaccine in comparison to the intramuscular (IM) administration on the piglets’ health and performance. A total of 187 suckling piglets of a PRRSV-positive commercial farrow-to-finish farm were assigned to four groups: group A—PRRSV ID, group B—PRRSV IM, group C—control ID, and group D—control IM. At 2 weeks of age, all the study piglets were either vaccinated with a PRRSV-1 MLV vaccine or injected with the vaccine adjuvant (controls). The collected blood serum samples were tested by ELISA and qRT-PCR. The side effects, body weight (BW), average daily gain (ADG), mortality rate, and lung and pleurisy lesions scores (LLS, PLS) were also recorded. The ELISA results indicated that the vaccination induced an important seroconversion at 4 and 7 weeks. Significant differences in the qRT-PCR results were noticed only at 10 weeks in group A vs. group C (p < 0.01) and group B vs. group C (p < 0.05). High viral loads, as evidenced by the qRT-PCR Ct values, were noticed in animals of both non-vaccinated groups at 7, 10, and 13 weeks. An ID vaccination has a positive impact on the BW at the piglets’ slaughter, while both an ID and IM vaccination had a positive impact on the ADG. The mortality rate was lower in vaccinated groups at the finishing stage. The LLS and PLS were significantly lower in the vaccinated groups. In conclusion, our study demonstrated that the ID vaccination of suckling piglets with a PRRSV-1 MLV vaccine has a positive effect on the piglets’ health and performance, including an improved BW and a lower LLS and PLS index at their slaughter, as well as a decreased mortality rate at the growing/finishing stage.

Using Alphafold2 to Predict the Structure of the Gp5/M Dimer of Porcine Respiratory and Reproductive Syndrome Virus

Porcine reproductive and respiratory syndrome virus is a positive-stranded RNA virus of the family Arteriviridae. The Gp5/M dimer, the major component of the viral envelope, is required for virus budding and is an antibody target. We used alphafold2, an artificial-intelligence-based system, to predict a credible structure of Gp5/M. The short disulfide-linked ectodomains lie flat on the membrane, with the exception of the erected N-terminal helix of Gp5, which contains the antibody epitopes and a hypervariable region with a changing number of carbohydrates. The core of the dimer consists of six curved and tilted transmembrane helices, and three are from each protein. The third transmembrane regions extend into the cytoplasm as amphiphilic helices containing the acylation sites. The endodomains of Gp5 and M are composed of seven β-strands from each protein, which interact via β-strand seven. The area under the membrane forms an open cavity with a positive surface charge. The M and Orf3a proteins of coronaviruses have a similar structure, suggesting that all four proteins are derived from the same ancestral gene. Orf3a, like Gp5/M, is acylated at membrane-proximal cysteines. The role of Gp5/M during virus replication is discussed, in particular the mechanisms of virus budding and models of antibody-dependent virus neutralization.

Micro-Players of Great Significance-Host microRNA Signature in Viral Infections in Humans and Animals

Over time, more and more is becoming known about micro-players of great significance. This is particularly the case for microRNAs (miRNAs; miR), which have been found to participate in the regulation of many physiological and pathological processes in both humans and animals. One such process is viral infection in humans and animals, in which the host miRNAs—alone or in conjunction with the virus—interact on two levels: viruses may regulate the host’s miRNAs to evade its immune system, while the host miRNAs can play anti- or pro-viral roles. The purpose of this comprehensive review is to present the key miRNAs involved in viral infections in humans and animals. We summarize the data in the available literature, indicating that the signature miRNAs in human viral infections mainly include 12 miRNAs (i.e., miR-155, miR-223, miR-146a, miR-122, miR-125b, miR-132, miR-34a, miR -21, miR-16, miR-181 family, let-7 family, and miR-10a), while 10 miRNAs are commonly found in animals (i.e., miR-155, miR-223, miR-146a, miR-145, miR-21, miR-15a/miR-16 cluster, miR-181 family, let-7 family, and miR-122) in this context. Knowledge of which miRNAs are involved in different viral infections and the biological functions that they play can help in understanding the pathogenesis of viral diseases, facilitating the future development of therapeutic agents for both humans and animals.

cGAS Restricts PRRSV Replication by Sensing the mtDNA to Increase the cGAMP Activity

Porcine reproductive and respiratory syndrome virus (PRRSV) is an RNA virus that causes great economic losses globally to the swine industry. Innate immune RNA receptors mainly sense it during infection. As a DNA sensor, cyclic GMP-AMP synthase (cGAS) plays an important role in sensing cytosolic DNA and activating innate immunity to induce IFN-I and establish an antiviral cellular state. In contrast, the role of innate immune DNA sensors during PRRSV infection has not been elucidated. In this study, we found that cGAS facilitates the production of IFN-β during PRRSV infection. Western blot and virus titer assays suggested that cGAS overexpression suppressed the replication of multiple PRRSV strains, while knockout of cGAS increased viral titer and nucleocapsid protein expression. Besides, our results indicated that the mitochondria were damaged during PRRSV infection and leaked mitochondrial DNA (mtDNA) into the cytoplasm. The mtDNA in the cytoplasm co-localizes with the cGAS, and the cGAMP activity was increased when the cGAS was overexpressed during PRRSV infection. Furthermore, the cGAMP also possesses an anti-PRRSV effect. These results indicate for the first time that cGAS restricts PRRSV replication by sensing the mtDNA in the cytoplasm to increase cGAMP activity, which not only explains the molecular mechanism by which cGAS inhibits PRRSV replication but also provides research ideas for studying the role of the cGAS-STING signaling pathway in the process of RNA virus infection.

Effect of the host genotype at a Porcine Reproductive and Respiratory Syndrome (PRRS) resistance marker on evolution of the modified-live PRRS vaccine virus in pigs

Porcine Reproductive and Respiratory Syndrome, Porcine Reproductive and Respiratory Syndrome Virus, PRRS, Whole genome sequencing, quasispecies, WUR allele.

A rescued NADC30-like virus by reverse genetic manipulation exhibits moderate virulence and a promising application perspective

NADC30-like porcine reproductive and respiratory syndrome virus (PRRSV), which is highly homologous to the NADC30 strain isolated in the United States. The NADC30-like PRRSV was first reported in 2014 in China, where it spread and gradually caused an epidemic. Currently, growing research has shown that NADC30-like strains have greater propensity to recombine with other PRRSV strains, particularly the PPRSV vaccine virus used clinically, making the prevention and control of PRRSV highly complex. To carry out an in-depth molecular biology and virulence analysis, a full-length infectious clone of the NADC30-like strain was successfully constructed and rescued by reverse genetic manipulation. The rescued virus, rZJqz, was indistinguishable from its parental virus, ZJqz21, based on virological characteristics. Further animal experiments demonstrated that rZJqz retained similar pathogenicity and induced the typical clinical symptoms and viral shedding observed in the ZJqz21 challenge model. Together, these results provide a useful tool for further study of the biological characteristics and pathogenicity of NADC30-like strains. Moreover, these findings also provide a solid foundation for studying the recombination of different PRRSVs and developing new and effective universal vaccines in the future.

Point-of-Care and Label-Free Detection of Porcine Reproductive and Respiratory Syndrome and Swine Influenza Viruses Using a Microfluidic Device with Photonic Integrated Circuits

Swine viral diseases challenge the sector’s sustainability by affecting productivity and the health and welfare of the animals. The lack of antiviral drugs and/or effective vaccines renders early and reliable diagnosis the basis of viral disease management, underlining the importance of point-of-care (POC) diagnostics. A novel POC diagnostic device utilizing photonic integrated circuits (PICs), microfluidics, and information and communication technologies for the detection of porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza A (SIV) was validated using spiked and clinical oral fluid samples. Metrics including sensitivity, specificity, accuracy, precision, positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR) were calculated to assess the performance of the device. For PRRSV, the device achieved a sensitivity of 83.5%, specificity of 77.8%, and DOR values of 17.66, whereas the values for SIV were 81.8%, 82.2%, and 20.81, respectively. The POC device and PICs can be used for the detection of PRRSV and SIV in the field, paving the way for the introduction of novel technologies in the field of animal POC diagnostics to further optimize livestock biosecurity.

Combined Subcutaneous-Intranasal Immunization With Epitope-Based Antigens Elicits Binding and Neutralizing Antibody Responses in Serum and Mucosae Against PRRSV-2 and SARS-CoV-2

New vaccine design approaches, platforms, and immunization strategies might foster antiviral mucosal effector and memory responses to reduce asymptomatic infection and transmission in vaccinated individuals. Here, we investigated a combined parenteral and mucosal immunization scheme to induce local and serum antibody responses, employing the epitope-based antigens 3BT and NG19m. These antigens target the important emerging and re-emerging viruses PRRSV-2 and SARS-CoV-2, respectively. We assessed two versions of the 3BT protein, which contains conserved epitopes from the GP5 envelope protein of PRRSV-2: soluble and expressed by the recombinant baculovirus BacDual-3BT. On the other hand, NG19m, comprising the receptor-binding motif of the S protein of SARS-CoV-2, was evaluated as a soluble recombinant protein only. Vietnamese mini-pigs were immunized employing different inoculation routes: subcutaneous, intranasal, or a combination of both (s.c.-i.n.). Animals produced antigen-binding and neut1ralizing antibodies in serum and mucosal fluids, with varying patterns of concentration and activity, depending on the antigen and the immunization schedule. Soluble 3BT was a potent immunogen to elicit binding and neutralizing antibodies in serum, nasal mucus, and vaginal swabs. The vectored immunogen BacDual-3BT induced binding antibodies in serum and mucosae, but PRRSV-2 neutralizing activity was found in nasal mucus exclusively when administered intranasally. NG19m promoted serum and mucosal binding antibodies, which showed differing neutralizing activity. Only serum samples from subcutaneously immunized animals inhibited RBD-ACE2 interaction, while mini-pigs inoculated intranasally or via the combined s.c.-i.n. scheme produced subtle neutralizing humoral responses in the upper and lower respiratory mucosae. Our results show that intranasal immunization, alone or combined with subcutaneous delivery of epitope-based antigens, generates local and systemic binding and neutralizing antibodies. Further investigation is needed to evaluate the capability of the induced responses to prevent infection and reduce transmission.

The mycotoxin deoxynivalenol (DON) can deteriorate vaccination efficacy against porcine reproductive and respiratory syndrome virus (PRRSV) at subtoxic levels

Background

Feedgrain contamination with mycotoxins, including deoxynivalenol (DON, “vomitoxin”) is relatively frequently encountered. Pigs are particularly sensitive to the toxicity of DON. To assess the interplay between DON and porcine reproductive and respiratory syndrome virus (PRRSV), we performed an experimental DON exposure–PRRSV vaccination–challenge infection trial. Three-week-old piglets were divided into four groups. Groups I, II and III (10 animals/group) were vaccinated with a PRRSV modified live vaccine and 2 weeks later challenged with a heterologous field strain. While group I was not supplemented with DON, animals in groups II and III received DON for 4 weeks prior to challenge infection at levels that can be encountered in pig feed, employing a low-dose or high-dose regime (group II: 40 µg DON/kg body weight per day; group III: 80 µg DON/kg body weight per day, corresponding to approx. 1 or 2 mg DON/kg feed, respectively). Eight animals (group IV; unvaccinated, not DON exposed) served as control animals for the challenge infection.

Results

We assessed clinical signs, virus load in serum and various organs as well as antibody titres in the animals. All vaccinated animals mounted an efficient PRRSV-specific antibody response within 2 weeks, except for 20% of the animals receiving the higher DON dose. Upon virus challenge, the vaccinated animals in group I were protected from clinical signs. Vaccinated DON-exposed animals in group II and III were protected from clinical signs to a lesser extent. Clinical signs in group III receiving the higher dose of DON were as severe as in the (unvaccinated, not DON exposed) control group IV. The animals of group III also displayed lower antibody titres compared with the animals in group I and II.

Conclusions

The experimental vaccination/challenge study therefore revealed that exposure of pigs to DON for a period of 4 weeks deteriorates the efficacy of vaccination against clinical signs of PRRS.

Alterations in the expression level of visfatin in the lungs of piglets infected with PRRSV and its effect on PRRSV replication

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by PRRS virus (PRRSV), characterized by sow reproductive failure and respiratory symptoms in pigs of all ages. PRRSV mainly causes severe lung damage by invading alveolar macrophages. Visfatin is closely related to acute lung injury, immune response and inflammation along with virus invasion to the host. Therefore, the current study was performed to clarify the relationship between visfatin and PRRSV infection. We used ternary piglets to construct a piglet model to explore the expression of visfatin and tight junction protein in lung injury induced by PRRSV infection, and then further studied the inhibition effect of visfatin on PRRSV replication by PRRSV infection of Marc-145 cells. Our results indicated that both PRRSV attenuated and virulent infections could damage the lung tissues, which could not only lead to severe inflammatory reaction (such as increased expression of TNF-α, TGF-β, IL-8 and IL-10) in lung tissues of piglets, but also brought about the sharp decrease of ZO-1 and Tricellulin expressions resulting in impaired alveolar epithelial barrier. Meanwhile, we found significantly up-regulated expression of visfatin in lungs and serum of pigs after PRRSV infection that were related to both the degree of lung injury and the virulence of PRRSV strain. Moreover, visfatin might inhibit the PRRSV infection to Marc-145 cells in time dependent fashion. Hence, the current investigation provides the novel information about the effect of visfatin and PRRSV co-culture on Marc-145 cells and the effect of visfatin on PRRSV proliferation at different time points.

Immunogenic and antigenic analysis of recombinant NSP1 and NSP11 of PRRS virus

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped RNA virus in the order Nidovirales, family Arteriviridae, genus Betaarterivirus. Antibodies against nonstructural proteins (NSPs) from this virus can be found in pigs starting 4 days postinfection and they remain detectable for several months.

Objective

The goal of this study was to evaluate the immunogenicity and antigenic properties of recombinant proteins NSP1 and NSP11 expressed in Escherichia coli cells, as well as to assess the neutralization activity that they elicit.

Methods

We obtained the complete ORF‐1 genes coding for NSP1 and NSP11 from PRRSV using the VR‐2332 strain. Cloning was performed with the pET23a(+) vector with a histidine tag (His6), linearized by restriction enzyme digestion; the expression of the NSP1 and NSP11 clones was induced in OverExpress C41(DE3) chemically competent cells. Recombinant proteins were used to generate hyperimmune sera and we perform serological assays to confirm neutralizing antibodies.

Results

The expressed recombinant NSP1 and NSP11 were found to be immunogenic when injected in pigs, as well as demonstrated higher specificity in recognition of antigen in field sera from pigs positive infected with PRRSV. Furthermore, both NSP1 and NSP11 recombinant proteins elicited PRRSV neutralizing antibodies.

Conclusions

In this study, we demonstrated the immune humoral response to NSP 1 and NSP11, and neutralizing‐antibody response to PRRSV VR2332 strain in sera from hyperimmunized pigs.

MicroRNA-376b-3p Promotes Porcine Reproductive and Respiratory Syndrome Virus Replication by Targeting Viral Restriction Factor TRIM22

Porcine reproductive and respiratory syndrome virus is a major economically significant pathogen and has evolved several strategies to evade host's antiviral response and provide favorable conditions for survival. In the present study, we demonstrated that a host microRNA, miR-376b-3p, was upregulated by PRRSV infection through the viral components, nsp4 and nsp11, and miR-376b-3p can directly target tripartite motif-containing 22 (TRIM22) to impair its anti-PRRSV activity, thus facilitating the replication of PRRSV. Meanwhile, we found that TRIM22 induced degradation of the nucleocapsid protein (N) of PRRSV by interacting with N protein to inhibit PRRSV replication, and further study indicated that TRIM22 could enhance the activation of lysosomal pathway by interacting with LC3 to induce lysosomal degradation of N protein. In conclusion, PRRSV increased miR-376b-3p expression and hijacked the host miR-376b-3p to promote PRRSV replication by impairing the antiviral effect of TRIM22. Therefore, our finding outlines a novel strategy of immune evasion exerted by PRRSV, which is helpful for better understanding the pathogenesis of PRRSV. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) causes enormous economic losses each year in the swine industry worldwide. MicroRNAs (miRNAs) play important roles during viral infections via modulating the expression of viral or host genes at post-transcriptional level. TRIM22 has recently been identified as a key restriction factor that inhibited the replication of a number of human virus such as HIV, ECMV, HCV, HBV, IAV, and RSV. Here we showed that host miR-376b-3p could be up-regulated by PRRSV and functioned to impair the anti-PRRSV role of TRIM22 to facilitate PRRSV replication. Meanwhile, we found that TRIM22 inhibited the replication of PRRSV by interacting with viral N protein and accelerating its degradation through the lysosomal pathway. Collectively, the paper described a novel mechanism that PRRSV exploited the host miR-376b-3p to evade antiviral responses and provided a new insight into the study of virus-host interactions.

Andrographolide and Its Derivative Potassium Dehydrographolide Succinate Suppress PRRSV Replication in Primary and Established Cells via Differential Mechanisms of Action

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause significant economic loss worldwide and remains a serious threat to the pork industry. Currently, vaccination strategies provide limited protection against PRRSV infection, and consequently, new antiviral strategies are urgently required. Andrographolide (Andro) and its derivative potassium dehydrographolide succinate (PDS) have been used clinically in China and other Asian countries as therapies for inflammation-related diseases, including bacterial and viral infections, for decades. Here, we demonstrate that Andro and PDS exhibit robust activity against PRRSV replication in Marc-145 cells and primary porcine alveolar macrophages (PAMs). The two compounds exhibited broad-spectrum inhibitory activities in vitro against clinically circulating type 2 PRRSV GD-HD, XH-GD, and NADC30-like HNhx strains in China. The EC₅₀ values of Andro against three tested PRRSV strain infections in Marc-145 cells ranged from 11.7 to 15.3 μmol/L, with selectivity indexes ranging from 8.3 to 10.8, while the EC₅₀ values of PDS ranged from 57.1 to 85.4 μmol/L, with selectivity indexes ranging from 344 to 515. Mechanistically, the anti-PRRSV activity of the two compounds is closely associated with their potent suppression on NF-κB activation and enhanced oxidative stress induced by PRRSV infection. Further mechanistic investigations revealed that PDS, but not Andro, is able to directly interact with PRRSV particles. Taken together, our findings suggest that Andro and PDS are promising PRRSV inhibitors in vitro and deserves further in vivo studies in swine.

The C/EBPβ-Dependent Induction of TFDP2 Facilitates Porcine Reproductive and Respiratory Syndrome Virus Proliferation

Porcine reproductive and respiratory syndrome (PRRS) is an important infectious disease caused by porcine reproductive and respiratory syndrome virus (PRRSV), leading to significant economic losses in swine industry worldwide. Although several studies have shown that PRRSV can affect the cell cycle of infected cells, it is still unclear how it manipulates the cell cycle to facilitate its proliferation. In this study, we analyzed the mRNA expression profiles of transcription factors in PRRSV-infected 3D4/21 cells by RNA-sequencing. The result shows that the expression of transcription factor DP2 (TFDP2) is remarkably upregulated in PRRSV-infected cells. Further studies show that TFDP2 contributes to PRRSV proliferation and the PRRSV nucleocapsid (N) protein induces TFDP2 expression by activating C/EBPβ. TFDP2 positively regulates cyclin A expression and triggers a less proportion of cells in the S phase, which contributes to PRRSV proliferation. This study proposes a novel mechanism by which PRRSV utilizes host protein to regulate the cell cycle to favor its infection. Findings from this study will help us for a better understanding of PRRSV pathogenesis.

Palmitoylation of the envelope membrane proteins GP5 and M of porcine reproductive and respiratory syndrome virus is essential for virus growth

Porcine reproductive and respiratory syndrome virus (PRRSV), an enveloped positive-strand RNA virus in the Arteiviridae family, is a major pathogen affecting pigs worldwide. The membrane (glyco)proteins GP5 and M form a disulfide-linked dimer, which is a major component of virions. GP5/M are required for virus budding, which occurs at membranes of the exocytic pathway. Both GP5 and M feature a short ectodomain, three transmembrane regions, and a long cytoplasmic tail, which contains three and two conserved cysteines, respectively, in close proximity to the transmembrane span. We report here that GP5 and M of PRRSV-1 and -2 strains are palmitoylated at the cysteines, regardless of whether the proteins are expressed individually or in PRRSV-infected cells. To completely prevent S-acylation, all cysteines in GP5 and M have to be exchanged. If individual cysteines in GP5 or M were substituted, palmitoylation was reduced, and some cysteines proved more important for efficient palmitoylation than others. Neither infectious virus nor genome-containing particles could be rescued if all three cysteines present in GP5 or both present in M were replaced in a PRRSV-2 strain, indicating that acylation is essential for virus growth. Viruses lacking one or two acylation sites in M or GP5 could be rescued but grew to significantly lower titers. GP5 and M lacking acylation sites form dimers and GP5 acquires Endo-H resistant carbohydrates in the Golgi apparatus suggesting that trafficking of the membrane proteins to budding sites is not disturbed. Likewise, GP5 lacking two acylation sites is efficiently incorporated into virus particles and these viruses exhibit no reduction in cell entry. We speculate that multiple fatty acids attached to GP5 and M in the endoplasmic reticulum are required for clustering of GP5/M dimers at Golgi membranes and constitute an essential prerequisite for virus assembly.

Porcine reproductive and respiratory syndrome virus (PRRSV), an arterivirus in the order Nidovirales, is an important pathogen for pigs. Despite its importance in veterinary medicine, basic structural and functional features of its membrane proteins have not been elucidated. Here, we provide evidence for palmitoylation of the PRRSV major membrane proteins GP5 and M at a cluster of membrane-near cysteines. Fatty acid attachment is required for virus growth, since removal of all acylation sites from either M or GP5 prevents recue of infectious particles. Furthermore, viruses lacking individual acylation sites in M and GP5 grow to significantly lower titers in cell culture. The specific infectivity and cell entry of viruses lacking two acylation sites in Gp5 is, however, not reduced. Likewise, these viruses revealed no effect on dimerization of GP5 with M, its transport to budding sites, and incorporation into virus particles. Since cells transfected with a cDNA expressing non-acylated GP5, or non-acylated M release no virus-like particles into the supernatant we propose that the fatty acids are required for the budding process. They might trigger assembly of GP5/M dimers to form a coat inside the lipid bilayer that induces membrane curvature.

Research Relevant Background Lesions and Conditions: Ferrets, Dogs, Swine, Sheep, and Goats

Animal models provide a valuable tool and resource for biomedical researchers as they investigate biological processes, disease pathogenesis, novel therapies, and toxicologic studies. Interpretation of animal model data requires knowledge not only of the processes/diseases being studied but also awareness of spontaneous conditions and background lesions in the model that can influence or even confound the study results. Species, breed/stock, sex, age, anatomy, physiology, diseases (noninfectious and infectious), and neoplastic processes are model features that can impact the results as well as study interpretation. Here, we review these features in several common laboratory animal species, including ferret, dog (beagle), pig, sheep, and goats.

Commercial PRRS Modified-Live Virus Vaccines

Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) presents one of the challenging viral pathogens in the global pork industry. PRRS is characterized by two distinct clinical presentations; reproductive failure in breeding animals (gilts, sows, and boars), and respiratory disease in growing pigs. PRRSV is further divided into two species: PRRSV-1 (formerly known as the European genotype 1) and PRRSV-2 (formerly known as the North American genotype 2). A PRRSV-2 modified-live virus (MLV) vaccine was first introduced in North America in 1994, and, six years later, a PRRSV-1 MLV vaccine was also introduced in Europe. Since then, MLV vaccination is the principal strategy used to control PRRSV infection. Despite the fact that MLV vaccines have shown some efficacy, they were problematic as the efficacy of vaccine was often unpredictable and depended highly on the field virus. This paper focused on the efficacy of commercially available MLV vaccines at a global level based on respiratory disease in growing pigs, and maternal and paternal reproductive failure in breeding animals.

Antiviral Mechanism of Tea Polyphenols against Porcine Reproductive and Respiratory Syndrome Virus

Neither inactivated nor attenuated vaccines can effectively prevent and control the infection and spread of porcine reproductive and respiratory syndrome virus (PRRSV). Therefore, it is necessary to broaden new horizons and to conceive effective preventive strategies. The main components of Tea polyphenol (TPP) are catechins and their derivatives. TPP has many physiological activities and has certain antiviral and antifungal effects. However, whether TPP shows anti-PRRSV activity remains unclear. We found that TPP effectively inhibited PRRSV infection in Marc-145 cells by suppressing the stages of viral attachment, internalization, replication, and release. TPP exhibited a potent anti-PRRSV effect regardless of pre-treatment or post-treatment. In addition, we demonstrated that TPP restrained PRRSV-induced p65 entry into the nucleus to suppress the activation of the NF-κB signaling pathway, which ultimately leads to the inhibition of the expression of inflammatory cytokines. Furthermore, TPP limited the synthesis of viral non-structural protein 2 (nsp2), the core component of viral replication transcription complexes, which may contribute to the inhibition of viral RNA replication. TPP has the potential to develop into an effective antiviral agent for PRRSV prevention and control in the future.

Aspartic acid at residue 185 modulates the capacity of HP-PRRSV nsp4 to antagonize IFN-I expression

In a previous study, we have shown that highly-pathogenic PRRSV (HP-PRRSV) nonstructural protein 4 (nsp4) antagonizes type I IFN expression induced by poly(I:C). Here, we demonstrated that the mutation of Aspartic acid 185 (Asp185) impaired the ability of nsp4 to inhibit IFN-I production induced by poly(I:C). Subsequently, we verified that all the mutants at the residue 185, regardless of amino acid size (including Cys and Ser) and charge (including Glu and Lys), impaired nsp4 catalytic activity. However, when Asp185 in nsp4 was replaced by a similar structure amino acid Asparagine 185 (Asn185), nsp4 stayed but with a decreased protease activity. Importantly, the recombinant virus with Asn185 mutation in HP-PRRSV-nsp4 exhibited slower replication rate and higher ability to induce IFN-I expression compared with wild-type (wt) HP-PRRSV.

Vaccination Is a Suitable Tool in the Control of Aujeszky's Disease Outbreaks in Pigs Using a Population Dynamics P Systems Model

Simple Summary

Maximizing the efficiency of pork production in line with sustainability and environmental restrictions presents a challenge for the pig industry in the coming years. It is necessary to develop practices based on cost/benefit analyses of the effects of disease on animal performance. Diseases can be controlled in various ways, such as vaccination programs and management protocols, among others, to control pathogens. We have developed a model to disentangle the effects of management and vaccination strategies to control one of the most important pig viral diseases, Aujeszky disease. Our results suggest that after confirming the diagnosis, early vaccination of most of the population is critical to decrease the spread of the virus and minimize its impact on pig productivity. However, the effect of management is negligible for the control of this virus. Thus, this model can be used to evaluate preventive medicine programs in the control of known diseases and for new ones that could appear in the future.

Abstract

Aujeszky’s disease is one of the main pig viral diseases and results in considerable economic losses in the pork production industry. The disease can be controlled using preventive measures such as improved stock management and vaccination throughout the pig-rearing period. We developed a stochastic model based on Population Dynamics P systems (PDP) models for a standard pig production system to differentiate between the effects of pig farm management regimes and vaccination strategies on the control of Aujeszky’s disease under several different epidemiological scenarios. Our results suggest that after confirming the diagnosis, early vaccination of most of the population (>75%) is critical to decrease the spread of the virus and minimize its impact on pig productivity. The direct economic cost of an outbreak of Aujeszky’s disease can be extremely high on a previously uninfected farm (from 352–792 Euros/sow/year) and highlights the positive benefits of investing in vaccination measures to control infections. We demonstrate the usefulness of computational models as tools in the evaluation of preventive medicine programs aimed at limiting the impact of disease on animal production.

Resilience Effects of SGK1 and TAP1 DNA Markers during PRRSV Outbreaks in Reproductive Sows

The porcine reproductive and respiratory syndrome virus (PRRSV) is a major infectious stressor that causes serious health problems and productivity drops. Based on previous genome-wide analyses, we selected SGK1 and TAP1 as candidate genes for resilience, and genotyped three mutations, including a 3'UTR variant SGK1_rs338508371 and two synonymous variants TAP1_rs1109026889 and TAP1_rs80928141 in 305 Landrace × Large White sows. All polymorphisms affected the reproductive performance in the outbreak, but not during the endemic phase, thereby indicating a potential use of these markers for resilience. Moreover, some genotypes were associated with a stable performance across PRRSV phases. Thus, in the outbreak, the SGK1_rs338508371 AA sows had less piglets born alive (p < 0.0001) and more stillborns (p < 0.05) while other sows were able to keep their productivity. During the outbreak, TAP1_rs80928141 GG sows had less piglets born alive (p < 0.05) and both TAP1 polymorphisms influenced the number of mummies in an additive manner (p < 0.05). Remarkably, TAP1_rs80928141 AA sows had around one mummy more than GG sows (p < 0.01). Resilience to PRRSV could be improved by including the SGK1 and TAP1 markers in crossbreeding and/or selection schemes, as they contribute to maintaining a stable number of piglets born alive and lost, particularly mummies, despite the outbreak.

TREM2 suppresses the proinflammatory response to facilitate PRRSV infection via PI3K/NF-κB signaling

Triggering receptor expressed on myeloid cells 2 (TREM2) serves as an anti-inflammatory receptor, negatively regulating the innate immune response. TREM2 is mainly expressed on dendritic cells and macrophages, the target cells of porcine reproductive and respiratory syndrome virus (PRRSV). Thus, we investigated the potential role of TREM2 in PRRSV infection in porcine alveolar macrophages (PAMs). We found that there was an increased expression of TREM2 upon PRRSV infection in vitro. TREM2 silencing restrained the replication of PRRSV, whereas TREM2 overexpression facilitated viral replication. The cytoplasmic tail domain of TREM2 interacted with PRRSV Nsp2 to promote infection. TREM2 downregulation led to early activation of PI3K/NF-κB signaling, thus reinforcing the expression of proinflammatory cytokines and type I interferons. Due to the enhanced cytokine expression, a disintegrin and metalloproteinase 17 was activated to promote the cleavage of membrane CD163, which resulted in suppression of infection. Furthermore, exogenous soluble TREM2 (sTREM2)-mediated inhibition of PRRSV attachment might be attributed to its competitive binding to viral envelope proteins. In pigs, following PRRSV challenge in vivo, the expression of TREM2 in lungs and lymph nodes as well as the production of sTREM2 were significantly increased. These novel findings indicate that TREM2 plays a role in regulating PRRSV replication via the inflammatory response. Therefore, our work describes a novel antiviral mechanism against PRRSV infection and suggests that targeting TREM2 could be a new approach in the control of the PRRSV infection.

Induction of mucosal immunity against pathogens by using recombinant baculoviral vectors: Mechanisms, advantages, and limitations

Over 90% of pathogens of medical importance invade the organism through mucosal surfaces, which makes it urgent to develop safe and effective mucosal vaccines and mucosal immunization protocols. Besides, parenteral immunization does not provide adequate protective immunity in mucosal surfaces. Effective mucosal vaccination could protect local and systemic compartments and favor herd immunity. Although various mucosal adjuvants and Ag-delivery systems have been developed, none has filled the gap to control diseases caused by complex mucosal pathogens. Among the strategies to counteract them, recombinant virions from the baculovirus Autographa californica multiple nucleopolyhedrovirus (rAcMNPV) are useful vectors, given their safety and efficacy to produce mucosal and systemic immunity in animal infection models. Here, we review the immunogenic properties of rAcMNPV virions from the perspectives of mucosal immunology and vaccinology. Some features, which are analyzed and extrapolated from studies with different particulate antigens, include size, shape, surface molecule organization, and danger signals, all needed to break the tolerogenic responses of the mucosal immune tissues. Also, we present a condensed discussion on the immunity provided by rAcMNPV virions against influenza virus and human papillomavirus in animal models. Through the text, we highlight the advantages and limitations of this experimental immunization platform.

Molecular and Cellular Mechanisms for PRRSV Pathogenesis and Host Response to Infection

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PRRSV has evolved to arm with various strategies to modify host antiviral response.

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Viral modulation of homeostatic cellular processes provides favorable conditions for PRRSV survival during infection.

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PRRSV modulation of cellular processes includes pathways for interferons, apoptosis, microRNAs, cytokines, autophagy, and viral genome recombination.

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused tremendous amounts of economic losses to the swine industry for more than three decades, but its control is still unsatisfactory. A significant amount of information is available for host cell-virus interactions during infection, and it is evident that PRRSV has evolved to equip various strategies to disrupt the host antiviral system and provide favorable conditions for survival. The current study reviews viral strategies for modulations of cellular processes including innate immunity, apoptosis, microRNAs, inflammatory cytokines, and other cellular pathways.

Vaccination of Mice with Listeria ivanovii Expressing the Truncated M Protein of Porcine Reproductive and Respiratory Syndrome Virus Induces both Antigen-Specific CD4+ and CD8+ T Cell-Mediated Immunity

Porcine reproductive and respiratory syndrome (PRRS), a serious disease of swine caused by the PRRS virus (PRRSV), had a severe economic impact worldwide. As commonly used PRRS vaccines, the attenuated or inactivated vaccines, provide unsatisfactory immune protection, a new PRRS vaccine is urgently needed. In this study, a part of the PRRSV ORF6 gene (from 253 to 519 bp) encoding the hydrophilic domain of PRRSV M protein was integrated into two Listeria strains via homologous recombination to generate two PRRS vaccine candidates, namely LI-M' and LM-ΔactAplcB-M'. Both candidate vaccines showed similar growth rate as their parent strains in culture media, but presented different bacterial loads in target organs. As the integrated heterogenous gene was not expressed, LM-ΔactAplcB-M' was excluded from the immunological test. In a mouse model, LI-M' provoked both CD4+ and CD8+ T cell-mediated immunity. In addition, LI-M' boosting dramatically enhanced CD8+ T cell-mediated immunity without affecting the response intensity of CD4+ T cell-mediated immunity. All of these data suggest that LI-M' is a promising PRRS vaccine candidate.

Genetic relationships of antibody response, viremia level, and weight gain in pigs experimentally infected with porcine reproductive and respiratory syndrome virus1

Genetic and antigenic variability between Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) isolates has encumbered vaccine development. Here, the genetic basis of PRRSV antibody response was assessed using data from experimental infection trials of commercial crossbred weaner pigs across with one of two distinct PRRSV isolates, NVSL-97-7895 (~750 pigs) and KS-2006-72109 (~450 pigs). Objectives were to estimate the genetic parameters of antibody response, measured as the sample to positive ratio (S:P) of PRRSV N-protein specific IgG in serum at 42 d post infection (dpi); assess the relationship of S:P at 42 dpi with serum viremia and growth under infection; and identify genomic regions associated with S:P at 42 dpi. Estimates of heritability of S:P at 42 dpi for NVSL and KS06 were 0.31 ± 0.09 and 0.40 ± 0.10 and appeared to be under similar genetic control (genetic correlation 0.73 ± 0.39). Estimates of genetic correlations of S:P were generally weak with viral load (NVSL: -0.20 ± 0.18; KS06: -0.69 ± 0.20), measured as area under the curve of log10 serum viremia from 0 to 21 dpi, and with weight gain (WG) from 0 to 42 dpi (NVSL: -0.38 ± 0.19; KS06: -0.08 ± 0.25). However, genetic correlations of S:P at 42 dpi with daily serum viremia and with 3-d WG revealed dynamic relationships, with S:P at 42 dpi having the strongest negative genetic correlations with daily viremia when IgG production starts (10-20 dpi), and negative genetic correlations with WG early after infection but positive later on. This suggests that animals that placed more emphasis on immune response early in infection reaped benefits of that later in infection by more effectively clearing the virus. The WUR10000125 SNP on SSC4, previously associated with response to PRRSV, did not have a significant effect on S:P at 42 dpi (P > 0.05) but genotype-specific genetic correlations of S:P with daily viremia and 3-d WG suggested that the lower WG of pigs with the unfavorable AA WUR10000125 genotype may be due to their utilization of a more energetically costly host response compared to pigs with the favorable genotype. Genome-wide association studies identified three SNPs in the Major Histocompatibility Complex associated with S:P that explained ~10 (NVSL) and 45% (KS06) of the genetic variance but were not associated with viremia or WG. In conclusion, antibody response to PRRSV infection is a possible biomarker for improved host response to PRRSV infection.

WITHDRAWN: Porcine reproductive and respiratory syndrome virus (PRRSV) inhibition with engineered Cas13d

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Effect of polymorphisms in porcine guanylate-binding proteins on host resistance to PRRSV infection in experimentally challenged pigs

Guanylate-binding proteins (GBP1 and GBP5) are known to be important for host resistance against porcine reproductive and respiratory syndrome virus (PRRSV) infection. In this study, the effects of polymorphisms in GBP1 (GBP1E2 and WUR) and GBP5 on host immune responses against PRRSV were investigated to elucidate the mechanisms governing increased resistance to this disease. Seventy-one pigs [pre-genotyped based on three SNP markers (GBP1E2, WUR, and GBP5)] were assigned to homozygous (n = 36) and heterozygous (n = 35) groups and challenged with the JA142 PRRSV strain. Another group of nineteen pigs was kept separately as a negative control group. Serum and peripheral blood mononuclear cells (PBMCs) were collected at 0, 3, 7, 14, 21 and 28 days post-challenge (dpc). Viremia and weight gain were measured in all pigs at each time point, and a flow cytometry analysis of PBMCs was performed to evaluate T cell activation. In addition, 15 pigs (5 pigs per homozygous, heterozygous and negative groups) were sacrificed at 3, 14 and 28 dpc, and the local T cell responses were evaluated in the lungs, bronchoalveolar lavage cells (BALc), lymph nodes and tonsils. The heterozygous pigs showed lower viral loads in the serum and lungs and higher weight gains than the homozygous pigs based on the area under the curve calculation. Consistently, compared with the homozygous pigs, the heterozygous pigs exhibited significantly higher levels of IFN-α in the serum, proliferation of various T cells (γδT, Th1, and Th17) in PBMCs and tissues, and cytotoxic T cells in the lungs and BALc. These results indicate that the higher resistance in the pigs heterozygous for the GBP1E2, WUR and GBP5 markers could be mediated by increased antiviral cytokine (IFN-α) production and T cell activation.

A novel intracellularly expressed NS5B-specific nanobody suppresses bovine viral diarrhea virus replication

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BVDV NS5B-specific nanobodies were identified.

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NS5B-specific nanobody Nb1 suppresses BVDV infection and replication.

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Nb1 interacts with NS5B protein during BVDV infection.

Bovine viral diarrhea virus (BVDV) infection causes significant economic losses to the cattle industry worldwide and still represents a huge pressure on agricultural production. Thus, the development of novel anti-BVDV strategies are urgently needed. The nonstructural protein 5 (NS5B) of BVDV is essential for viral replication. Further, the camel single-domain antibody (nanobody) represents a promising antiviral approach with the advantages of small size, stable structure, high specificity and solubility, and the recognition of specific epitopes. However, no NS5B-specific nanobodies against BVDV have been reported. In this study, NS5B-specific nanobodies were isolated from a phage display library of variable domains of Camellidae heavy chain-only antibodies (VHHs). Further, an MDBK cell line stably expressing Nb1 was established to explore antiviral activity. Results showed that Nb1 could markedly suppress BVDV replication and interact with the BVDV NS5B protein. This suggests that nanobodies have potential for the development of novel antiviral drugs against BVDV infection.

Fluorescence resonance energy transfer combined with asymmetric PCR for broad and sensitive detection of porcine reproductive and respiratory syndrome virus 2

With its ever-increasing viral genetic diversity, accurate diagnosis of porcine reproductive and respiratory syndrome virus (PRRSV) infection is indispensable for PRRSV control. Here, a sensitive graphene oxide (GO)-based FRET method was developed to detect PRRSV-2 based on the ability of GO to quench fluorophore by fluorescence resonance energy transfer (FRET). Using primers and a fluorophore-labeled ssDNA probe targeting a conserved region between the PRRSV M gene and 3'UTR, asymmetric PCR specifically amplified viral ssDNA that could anneal with probe to generate dsDNA only in the presence of virus. Upon exonuclease III treatment to release the probe fluorophore, which degrades dsDNA with blunt ends or recessed 3´-termini, the ssDNA annealed with other probe to generate enhanced fluorescence. This GO-based FRET assay specifically detected both classical and highly pathogenic PRRSV, with analytical sensitivity approaching 10 copies/μL, similar to that of real-time PCR but greater than that of conventional reverse transcription PCR (RT-PCR). Consistent with real-time RT-PCR detection, the assay developed here exhibited high diagnostic sensitivity for virus detection of sera from experimentally and naturally infected pigs. Thus, this novel GO-based FRET assay combined with asymmetric PCR detection is sensitive and specific and will be valuable for future PRRSV diagnosis.

Restriction of porcine reproductive and respiratory syndrome virus replication by galectin-1

Porcine reproductive and respiratory syndrome virus (PRRSV) causes great economic losses to the swine industry globally; however, effective control measures for this virus are limited. Here, we screened a porcine alveolar macrophage (PAM) cDNA library with a yeast two-hybrid system to reveal that galectin-1 (Gal-1), an endogenous innate immune protein encoded by LGALS1, interacts with nonstructural protein 11 (Nsp11) of PRRSV. Western blotting and viral titer assays indicated that Gal-1 overexpression suppressed replication in multiple PRRSV strains (P < 0.001), whereas Gal-1 knockdown or knockout increased viral titer and nucleocapsid protein expression. The Gal-1-specific anti-PRRSV effect was associated with the endoribonuclease domain of Nsp11 through inactivation of interferon-antagonist function and stimulation of interferon-stimulated gene expression. Additionally, Gal-1 interacted with PRRSV E protein but not with PRRSV glycoproteins, and recombinant Gal-1 treatment inhibited PRRSV in PAMs and MARC-145 cells. Furthermore, Gal-1 inhibited replication in multiple viruses, including equine arteritis virus, porcine epidemic diarrhea virus, pseudorabies virus, Japanese encephalitis virus, and classical swine fever virus, suggesting its potential broad application for antiviral strategies. Our findings provide insight into the important role of Gal-1 in PRRSV pathogenesis and its potential use as a novel therapeutic target against PRRSV infection.

Improving the management procedures in farms infected with the Porcine Reproductive and Respiratory Syndrome virus using PDP models

Pig meat production need to be built up in the future due to the increase of the human population worldwide. To address this challenge, there is plenty of room for improvement in terms of pig production efficiency that could be severely hampered by the presence of diseases. In this sense, Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is one of the most costly disease present in industrial pork production in Europe and North America. We have developed a model to analyze the effect of different management procedures to control this important virus in different epidemiological scenarios. Our results clearly suggest that no cross-fostering during lactation and the maintaining of litter integrity significantly decrease the number of sick and dead animals during the rearing period compared to scenarios where cross-fostering and no litter integrity are practiced. These results highlight the relevance of different management strategies to control PRRSV and quantify the effect of limiting cross-fostering and avoiding mixing animals from different litters in PRRSV positive farms to optimize animal production. Our findings will allow pig farmers to apply these management procedures to control this disease under field conditions in a very cost-effective way.

Arterivirus nsp4 Antagonizes Interferon Beta Production by Proteolytically Cleaving NEMO at Multiple Sites

Equine arteritis virus (EAV) and porcine reproductive and respiratory syndrome virus (PRRSV) represent two members of the family Arteriviridae and pose major threats for the horse- and swine-breeding industries worldwide. A previous study suggested that PRRSV nsp4, a 3C-like protease, antagonizes interferon beta (IFN-β) production by cleaving the NF-κB essential modulator (NEMO) at a single site, glutamate 349 (E349). Here, we demonstrated that EAV nsp4 also inhibited virus-induced IFN-β production by targeting NEMO for proteolytic cleavage and that the scission occurred at four sites: E166, E171, glutamine 205 (Q205), and E349. Additionally, we found that, besides the previously reported cleavage site E349 in NEMO, scission by PRRSV nsp4 took place at two additional sites, E166 and E171. These results imply that while cleaving NEMO is a common strategy utilized by EAV and PRRSV nsp4 to antagonize IFN induction, EAV nsp4 adopts a more complex substrate recognition mechanism to target NEMO. By analyzing the abilities of the eight different NEMO fragments resulting from EAV or PRRSV nsp4 scission to induce IFN-β production, we serendipitously found that a NEMO fragment (residues 1 to 349) could activate IFN-β transcription more robustly than full-length NEMO, whereas all other NEMO cleavage products were abrogated for the IFN-β-inducing capacity. Thus, NEMO cleavage at E349 alone may not be sufficient to completely inactivate the IFN response via this signaling adaptor. Altogether, our findings suggest that EAV and PRRSV nsp4 cleave NEMO at multiple sites and that this strategy is critical for disarming the innate immune response for viral survival.IMPORTANCE The arterivirus nsp4-encoded 3C-like protease (3CLpro) plays an important role in virus replication and immune evasion, making it an attractive target for antiviral therapeutics. Previous work suggested that PRRSV nsp4 suppresses type I IFN production by cleaving NEMO at a single site. In contrast, the present study demonstrates that both EAV and PRRSV nsp4 cleave NEMO at multiple sites and that this strategy is essential for disruption of type I IFN production. Moreover, we reveal that EAV nsp4 also cleaves NEMO at glutamine 205 (Q205), which is not targeted by PRRSV nsp4. Notably, targeting a glutamine in NEMO for cleavage has been observed only with picornavirus 3C proteases (3Cpro) and coronavirus 3CLpro In aggregate, our work expands knowledge of the innate immune evasion mechanisms associated with NEMO cleavage by arterivirus nsp4 and describes a novel substrate recognition characteristic of EAV nsp4.

Perturbation of Thymocyte Development Underlies the PRRS Pandemic: A Testable Hypothesis

Porcine reproductive and respiratory syndrome virus (PRRSV) causes immune dysregulation during the Critical Window of Immunological Development. We hypothesize that thymocyte development is altered by infected thymic antigen presenting cells (TAPCs) in the fetal/neonatal thymus that interact with double-positive thymocytes causing an acute deficiency of T cells that produces "holes" in the T cell repertoire allowing for poor recognition of PRRSV and other neonatal pathogens. The deficiency may be the result of random elimination of PRRSV-specific T cells or the generation of T cells that accept PRRSV epitopes as self-antigens. Loss of helper T cells for virus neutralizing (VN) epitopes can result in the failure of selection for B cells in lymph node germinal centers capable of producing high affinity VN antibodies. Generation of cytotoxic and regulatory T cells may also be impaired. Similar to infections with LDV, LCMV, MCMV, HIV-1 and trypanosomes, the host responds to the deficiency of pathogen-specific T cells and perhaps regulatory T cells, by "last ditch" polyclonal B cell activation. In colostrum-deprived PRRSV-infected isolator piglets, this results in hypergammaglobulinemia, which we believe to be a "red herring" that detracts attention from the thymic atrophy story, but leads to our second independent hypothesis. Since hypergammaglobulinemia has not been reported in PRRSV-infected conventionally-reared piglets, we hypothesize that this is due to the down-regulatory effect of passive maternal IgG and cytokines in porcine colostrum, especially TGFβ which stimulates development of regulatory T cells (Tregs).