Porcine reproductive and respiratory syndrome virus genetic variability a management and diagnostic dilemma

First study to describe the prevalence and epidemiology of African swine fever, classical swine fever, porcine reproductive and respiratory syndrome and swine flu in Kazakhstan

BACKGROUND

Kazakhstan, the ninth-largest country in the world, located in Central Asia and bordering China, Kyrgyzstan, Russia, Turkmenistan, and Uzbekistan, hosts a diverse population of domestic pigs across various environments, providing potential hosts for highly pathogenic viral diseases of swine. Here we monitored African Swine Fever Virus (ASFV), Classical Swine Fever Virus (CSFV), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and Swine Influenza Virus (SIV).

RESULTS

During the spring and fall of 2019, we sampled 1,459 domestic pigs in northern, central and eastern Kazakhstan. Samples were tested for antibodies by ELISA and for viral genomes by qPCR and RT-qPCR. No antibodies against ASFV or ASFV DNA were detected in sampled animals. Of the 84 farms sampled, 16.6% had at least one animal vaccinated against CSF. Seropositive pigs were found on a farm in Oskemen with no history of vaccination against CSFV. No CSFV RNA was detected in the blood of the sampled animals. Only 12.2% of the animals tested were vaccinated against PRRS with live-attenuated vaccines. The true animal-level seroprevalence of PRRS on unvaccinated farms was 16.6%. PRRSV RNA was detected in 17 unvaccinated animals in Pavlodar oblast on farms that were vaccinated against PRRS. The identified PRRSV-1 strains belonged to subtype 1 and clustered with the PRRS DV vaccine virus strain. A large proportion of the pigs had antibodies against SIV, with true animal-level seroprevalence of 35.9% and herd-level seroprevalence of 23.2%. Antibodies against the influenza A viruses of hemagglutinin subtypes H1 and H3 were found in the examined pigs. None of the animals were vaccinated against SIV. The variable 'commercial farming' showed an association with PRRSV and IAV seroprevalence. Of the unvaccinated farms, 9% were co-infected with PRRSV and SIV.

CONCLUSIONS

Results confirm the domestic pig population in Kazakhstan was not infected with ASFV but indicated exposure to PRRSV and SIV. This underscores the need for monitoring these infections in the region to manage their impact.

Nanobody-based competitive enzyme-linked immunosorbent assay for detecting antibodies of porcine reproductive and respiratory syndrome virus

The pandemic of porcine reproductive and respiratory syndrome (PRRS) continues a global threat to the swine industry and causes huge economic losses. Large-scale serological surveillance, particularly through enzyme-linked immunosorbent assay (ELISA), is an effective measure for PRRS control. Nanobodies have been used in diagnostic immunoassays due to their high affinity and specificity. In this study, two novel nanobodies against N protein of PRRSV were generated that exhibited ability to block the recognition of serum antibodies to N protein. A high-affinity nanobody was conjugated with horseradish peroxidase (HRP), then nanobody-based competitive ELISA (cELISA) was subsequently developed to detect antibodies against both genotypes 1 and 2 PRRSV. Notably, the developed cELISA exhibited enhanced sensitivity, specificity and reproducibility. The comparative analysis demonstrated a high agreement of 96.69 % between the cELISA and a commercial ELISA kit. Collectively, the developed nanobody-based cELISA can be used for epidemiological study of PRRSV infection and immune evaluations with advantages of simple operation and low costing.

A serologic marker attenuated live vaccine protects piglets against highly pathogenic porcine reproductive and respiratory syndrome virus infection

Currently, there are no commercial serologic marker or differentiation of infected and vaccinated animal (DIVA) vaccines for the eradication of porcine reproductive and respiratory syndrome virus (PRRSV) infection from pig farms. In a previous study, a nanobody-based competitive ELISA (cELISA) was specifically developed to detect anti-genotype 2 PRRSV (PRRSV-2) antibodies. On the basis of the epitope recognized by the nanobody and the prevalence of PRRSV-2 infection in China, a DIVA vaccine candidate strain was designed and evaluated in the present study. First, an infectious cDNA clone based on the genomic sequence of the highly pathogenic PRRSV-2 (HP-PRRSV) isolate SX-HD was constructed and named rSX-HD. Using the infectious clone as the backbone, a chimeric infectious cDNA clone in which the gene encoding the nucleocapsid (N) protein was replaced with the gene encoding the genotype 1 PRRSV N protein was generated and named rSX-HD2M1. The chimeric PRRSV rSX-HD2M1 was subsequently rescued successfully in Marc-145 cells, which were then passaged for 120 generations for attenuation. A safety study indicated that rSX-HD2M1-F120 is not pathogenic to piglets. In vivo inoculation and challenge experiments suggested that rSX-HD2M1-F120 vaccination significantly reduced serum viral loads and lung tissue lesions and that vaccinated piglets did not show any clinical symptoms or histopathological changes. Furthermore, this recombinant marker virus, in conjunction with the previously developed nanobody-based cELISA, enables serological differentiation between marker virus-infected animals and those infected with wild-type PRRSV-2. These results suggest that rSX-HD2M1-F120 is a good candidate for providing a live attenuated DIVA vaccine against PRRSV-2 infection in piglets.

Evaluating postmortem tongue fluids as a tool for monitoring PRRSV and IAV in the post-wean phases of swine production

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) and influenza A virus (IAV) are swine pathogens that can significantly impact the performance of post-weaning pigs. While oral fluid (OF) samples are widely used for monitoring these viruses, postmortem tongue fluid (TF) samples present a cost-effective alternative with potential advantages in viral detection. This study aimed to compare the performance of TF and OF samples collected from nursery and finishing pig herds in detecting PRRSV and IAV using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). A Bayesian latent class model was used to estimate diagnostic sensitivity and specificity for TF and OF under the assumption of conditional independence. The study also examined the relationship between mortality rates and RT-qPCR outcomes, the success rate of Sanger sequencing for the PRRSV ORF-5 region, and the effect of pooling daily aggregated TF samples on the probability of PRRSV detection.

RESULTS

IAV was detected in 34.9% of OF samples and 30.2% of TF samples, while PRRSV was identified in 67.4% of OF and 53.5% of TF samples. TF samples had a significantly lower mean Ct for PRRSV (29.1) compared to OF samples (32.8) but had a similar Ct (30.9) to OF (29.7) for IAV. The hierarchical latent class Bayesian model estimated the sensitivity and specificity values for OF as 37.3% and 61.7% for IAV, and 64.3% and 35.1% for PRRSV. The estimated sensitivity and specificity values for TF were 33.5% and 66.0% for IAV, and 53.0% and 47.0% for PRRSV. Among 22 matched TF and OF pairs submitted for PRRSV sequencing, 45.5% of OF samples and 63.6% of TF samples were successfully sequenced, with the higher success rate for TF attributed to having lower Ct values. Additionally, mortality rates were notably higher when PRRSV was detected, especially in cases with concurrent IAV detection. Regarding sample pooling, our results indicated that pooling TF samples significantly increased detection probabilities, with a 1/7 dilution achieving a 79% RT-qPCR detection rate, compared to a detection rate of 14.3% when testing a single day's TF sample from a week with only one positive day.

CONCLUSION

The findings support the use of TF samples as a viable complement or alternative to OF samples for PRRSV and IAV surveillance in post-weaning pigs when mortalities are available. The cost-efficiency of TF sampling can enhance monitoring compliance, improve early pathogen detection, and facilitate timely responses to emerging threats in swine production. This study advocates for the adoption of TF as a risk-based sampling strategy in nursery and grow-finish settings, complementing live animal samples such as OF, ultimately contributing to better herd health management.

Recombination and pathogenicity analysis of NADC30-like and QYYZ-like PRRSV strains in South China

Since 2010, the Lineage 1 (NADC30-like) and Lineage 3 (QYYZ-like) strains of PRRSV-2 have become widespread in China, undergoing recombination and resulting in varying virulent and immune-evading mutants that have severely impacted the pig farming industry. In this study, we isolated one NADC30-like strain (GXHX20211106) and one QYYZ-like strain (GXGG202007) from pig serum samples collected in southern China. Comparative genomic analysis revealed that GXHX20211106 shares 90 % identity with NADC30, while GXGG202007 shows 91.4 % similarity to QYYZ. Both strains exhibit characteristic amino acids deletions or insertions in the Nsp2 region. Phylogenetic analyses further classified GXHX20211106 within Lineage 1.8 (NADC30-like) and GXGG202007 in Lineage 3 (QYYZ-like). Recombination analysis demonstrated that GXHX20211106 resulted from recombination between NADC30-like and HP-PRRSV-like strains, while GXGG202007 originated from recombination events involving QYYZ-like, VR-2332-like, and HP-PRRSV-like strains. Pathogenicity studies in piglets indicated that both isolates caused moderate clinical signs, with GXHX20211106 showing higher virulence compared to GXGG202007. No deaths were recorded in the infected piglets. These findings highlight the critical role of recombination in shaping PRRSV virulence and underscore the need for ongoing surveillance and control measures to mitigate the impact of recombinant PRRSV strains in southern China.

Genomic RNA recombination of porcine reproductive and respiratory syndrome virus and other arteriviruses

Arteriviruses in the Nidovirales order are single-stranded positive-sense RNA viruses infecting mammals. Arteriviruses are recognized for causing various clinical diseases, ranging from asymptomatic infections to severe conditions like respiratory syndromes and viral hemorrhagic fever. Notably, arteriviruses exhibit a high frequency of RNA recombination, and their robust recombination rates are a crucial factor in recurrent outbreaks. The recombination events also shape the countermeasures employed by arteriviruses during virus-host co-evolution and confer specific evolutionary benefits to viruses, implicating a role as a selective advantage in viral adaptation. This review delves into the molecular basis of RNA recombination in arteriviruses, the bioinformatics tools and methodologies used to visualize evolutionary relationships, and the identification of recombination breakpoints. Significant recombination events are highlighted for PRRSV and other arteriviruses, illustrating the profound implications of recombination for viral evolution and pathogenesis. Recombination between field viruses and between field viruses and vaccine strains can generate new variants with altered antigenic profiles and virulence, leading to diagnostic failure, severe clinical outcomes, and reduced vaccine efficacy. Despite the advances, further research is needed to understand recombination rates and hotspots, as well as to develop potential antiviral strategies and diagnostic approaches for arteriviruses.

Identification and biophysical characterization of epitope atlas of Porcine Reproductive and Respiratory Syndrome Virus

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) have been a critical threat to swine health since 1987 due to its high mutation rate and substantial economic loss over half a billion dollar in USA. The rapid mutation rate of PRRSV presents a significant challenge in developing an effective vaccine. Even though surveillance and intervention studies have recently (2019) unveiled utilization of PRRSV glycoprotein 5 (GP5; encoded by ORF5 gene) to induce immunogenic reaction and production of neutralizing antibodies in porcine populations, the future viral generations can accrue escape mutations. In this study we identify 63 porcine-PRRSV protein-protein interactions which play primary or ancillary roles in viral entry and infection. Using genome-proteome annotation, protein structure prediction, multiple docking experiments, and binding energy calculations, we identified a list of 75 epitope locations on PRRSV proteins crucial for infection. Additionally, using machine learning-based diffusion model, we designed 56 stable immunogen peptides that contain one or more of these epitopes with their native tertiary structures stabilized through optimized N- and C-terminus flank sequences and interspersed with appropriate linker regions. Our workflow successfully identified numerous known interactions and predicted several novel PRRSV-porcine interactions. By leveraging the structural and sequence insights, this study paves the way for more effective, high-avidity, multi-valent PRRSV vaccines, and leveraging neural networks for immunogen design.

Prevalence and genetic diversity of PRRSV in Sichuan province of China from 2021 to 2023: Evidence of an ongoing epidemic transition

Porcine reproductive and respiratory syndrome (PRRS) significantly impacts the global swine industry. Sichuan province, a key pig breeding center in China, has limited data on the molecular epidemiology of PRRS Virus (PRRSV). To address this, 1618 suspected PRRSV samples were collected from 2021 to 2023, with a prevalence rate of 39.74% (643/1618). Phylogenetic analysis showed PRRSV-2 as dominant (95.65%, 615/643), with PRRSV-1 at 4.35% (28/643). PRRSV-2 strains were further classified into NADC30-like (74.18%), NADC34-like (11.98%), C-PRRSV (5.44%), and HP-PRRSV (4.04%). The significant change in the proportions of different lineages indicates genomic divergence. NADC30-like strains exhibited significant amino acid mutations in ORF5, aiding immune evasion. Recombination analysis revealed complex patterns, primarily involving NADC30-like strains. This study highlights the genomic divergence of PRRSV in Sichuan, with NADC30-like strains becoming predominant and emerging strains like NADC34-like showing potential for further spread.

A Comprehensive Review on Porcine Reproductive and Respiratory Syndrome Virus with Emphasis on Immunity

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens in pig production worldwide and responsible for enormous production and economic losses. PRRSV infection in gestating gilts and sows induces important reproductive failure. Additionally, respiratory distress is observed in infected piglets and fattening pigs, resulting in growth retardation and increased mortality. Importantly, PRRSV infection interferes with immunity in the respiratory tract, making PRRSV-infected pigs more susceptible to opportunistic secondary pathogens. Despite the availability of commercial PRRSV vaccines for more than three decades, control of the disease remains a frustrating and challenging task. This paper provides a comprehensive overview of PRRSV, covering its history, economic and scientific importance, and description of the viral structure and genetic diversity. It explores the virus's pathogenesis, including cell tropism, viral entry, replication, stages of infection and epidemiology. It reviews the porcine innate and adaptative immune responses to comprehend the modulation mechanisms employed by PRRS for immune evasion.

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.

Lineage 1 PRRSVs infection induces hemorrhagic injury in intestines of piglets: Effects on complement and coagulation cascades

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly transmissible disease of significant concern in the pig industry. Previous studies have demonstrated that the XM-2020 strain (a lineage 1.8 PRRSV IA/2012/NADC30) can induce special hemorrhagic injury in the small intestines. However, the specific mechanism underlying this injurious effect remains incompletely understood. In this study, we examined the pathogenic properties of XM-2020 and YC-2020 strains (a lineage 1.5 PRRSV IA/2014/NADC34) in piglets. Animal pathogenic tests revealed that with either Lineage 1 PRRSVs strains XM-2020 or YC-2020 demonstrated pronounced intestinal hemorrhage and suppression of peripheral immunological organs, comparing to JXA1 infection. Transcriptome analysis of diseased small intestines unveiled that PRRSV infection stimulated oxidative and inflammatory reactions. Remarkably, we also observed activation of the complement system alongside a notable down-regulation of complement and coagulation cascade pathways in the Lineage 1 PRRSVs infection group. Based on these findings, we propose that the primary mechanism driving the hemorrhagic injury of the small intestine caused by Lineage 1 PRRSVs is the suppression of complement and coagulation cascades resulting from immunosuppression. This discovery deepens our understanding of the pathogenicity of PRRSV in the small intestine and provides promising ways out for the development of innovative strategies aimed at controlling PRRSV.

Heat shock protein 71 restricts mutation of porcine reproductive and respiratory syndrome virus nsp2 in vitro

porcine reproductive and respiratory syndrome (PRRS), caused by porcine reproductive and respiratory syndrome virus (PRRSV) infection, is an important swine infectious disease that causes substantial losses worldwide each year. PRRSV is a positive-sense single-stranded RNA virus that is highly susceptible to mutation and recombination, making vaccine and drug research for the disease extremely difficult. In this study, the binding of PRRSV nsp2 to HSP71 protein was detected by using the IP/MS technique. And the inhibitory effect of HSP71 on nsp2 antagonistic activity was validated by measuring NF-kB luciferase reporter. According to stress from inhibitory effects, the amino acid variation profile of PRRSV nsp2 under HSP71 stress was further analyzed using second-generation sequencing. Surprisingly, the results indicated that HSP71 pressure limits the random mutations of PRRSV nsp2 and maintains the dominant PRRSV strain within the population. Mutant strain showed weaker antagonistic activity and replication capability in cell. These results imply the binding of HSP71 with PRRSV nsp2 may lead to maintain the stability of highly virulent strains of PRRSV.

Isolation and pathogenicity comparison of two novel natural recombinant porcine reproductive and respiratory syndrome viruses with different recombination patterns in Southwest China

Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic losses in the swine industry. Frequent mutations and recombinations account for PRRSV immune evasion and the emergence of novel strains. In this study, we isolated and characterized two novel PRRSV-2 strains from Southwest China exhibiting distinct recombination patterns. They were designated SCABTC-202305 and SCABTC-202309. Phylogenetic results indicated that SCABTC-202305 was classified as lineage 8, and SCABTC-202309 was classified as lineage 1.8. Amino acid mutation analysis identified unique amino acid substitutions and deletions in ORF5 and Nsp2 genes. The results of the recombination analysis revealed that SCABTC-202305 is a recombinant with JXA1 as the major parental strain and NADC30 as the minor parental strain. At the same time, SCABTC-202309 is identified as a recombinant with NADC30 as the major parental strain and JXA1 as the minor parental strain. In this study, we infected piglets with SCABTC-202305, SCABTC-202309, or mock inoculum (control) to study the pathogenicity of these isolates. Although both isolated strains were pathogenic, SCABTC-202305-infected piglets exhibited more severe clinical signs and higher mortality, viral load, and antibody response than SCABTC-202309-infected piglets. SCABTC-202305 also caused more extensive lung lesions based on histopathology. Our findings suggest that the divergent pathogenicity observed between the two novel PRRSV isolates may be attributed to variations in the genetic information encoded by specific genomic regions. Elucidating the genetic determinants governing PRRSV virulence and transmissibility will inform efforts to control this devastating swine pathogen.IMPORTANCEPorcine reproductive and respiratory syndrome virus (PRRSV) is one of the most critical pathogens impacting the global swine industry. Frequent mutations and recombinations have made the control of PRRSV increasingly difficult. Following the NADC30-like PRRSV pandemic, recombination events involving PRRSV strains have further increased. We isolated two novel field PRRSV recombinant strains, SCABTC-202305 and SCABTC-202309, exhibiting different recombination patterns and compared their pathogenicity in animal experiments. The isolates caused higher viral loads, persistent fever, marked weight loss, moderate respiratory clinical signs, and severe histopathologic lung lesions in piglets. Elucidating correlations between recombinant regions and pathogenicity in these isolates can inform epidemiologic tracking of emerging strains and investigations into viral adaptive mechanisms underlying PRRSV immunity evasion. Our findings underscore the importance of continued genomic surveillance to curb this economically damaging pathogen.

Transition from one commercial porcine reproductive and respiratory syndrome modified-live virus vaccine to another in a breeding herd and impact on productivity

Porcine reproductive and respiratory syndrome (PRRS) continues to represent a significant cost to the swine industry and efforts are focused on prevention and mitigation of losses across production phases. Herein describes a PRRS modified-live virus (MLV) vaccinated breeding herd that changed commercial MLV vaccines to improve post-weaning performance. Two whole-herd vaccinations with a new PRRS MLV vaccine, administered 4 weeks apart, occurred without breeding herd production disruptions and with limited changes in diagnostic results. Replacement gilts tested PRRS virus negative 10 weeks post vaccination with the new MLV vaccine. Diagnostics were intermittently positive in the breeding herd and early nursery.

Computational antigenic insights into the novel NADC-34-like Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) isolate YC-2020

In this computational study, we advanced the understanding of the antigenic properties of the NADC-34-like isolate of the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), named YC-2020, relevant in veterinary pathology. We utilized sequence comparison analyses of the M and N proteins, comparing them with those of NADC34, identifying substantial amino acid homology that allowed us to highlight conserved epitopes and crucial variants. Through the application of Clustal Omega for multiple sequence alignment and platforms like Vaxijen and AllerTOP for predicting antigenic and allergenic potential, our analyses revealed important insights into the conservation and variation of epitopes essential for the development of effective diagnostic tools and vaccines. Our findings, aligned with initial experimental studies, underscore the importance of these epitopes in the development of targeted immunodiagnostic platforms and significantly contribute to the management and control of PRRSV. However, further studies are required to validate the computational predictions of antigenicity for this new viral isolate. This approach underscores the potential of computational models to enable ongoing monitoring and control of PRRSV evolution in swine. While this study provides valuable insights into the antigenic properties of the novel PRRSV isolate YC-2020 through computational analysis, it is important to acknowledge the limitations inherent to in silico predictions, specifically, the absence of laboratory validation.

Mass Spectrometry-Based Proteomic Analysis of Potential Host Proteins Interacting with GP5 in PRRSV-Infected PAMs

Porcine reproductive and respiratory syndrome virus (PRRSV) is a typical immunosuppressive virus causing a large economic impact on the swine industry. The structural protein GP5 of PRRSV plays a pivotal role in its pathogenicity and immune evasion. Virus-host interactions play a crucial part in viral replication and immune escape. Therefore, understanding the interactions between GP5 and host proteins are significant for porcine reproductive and respiratory syndrome (PRRS) control. However, the interaction network between GP5 and host proteins in primary porcine alveolar macrophages (PAMs) has not been reported. In this study, 709 GP5-interacting host proteins were identified in primary PAMs by immunoprecipitation coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Bioinformatics analysis revealed that these proteins were involved in multiple cellular processes, such as translation, protein transport, and protein stabilization. Subsequently, immunoprecipitation and immunofluorescence assay confirmed that GP5 could interact with antigen processing and presentation pathways related proteins. Finally, we found that GP5 may be a key protein that inhibits the antigen processing and presentation pathway during PRRSV infection. The novel host proteins identified in this study will be the candidates for studying the biological functions of GP5, which will provide new insights into PRRS prevention and vaccine development.

Development of a one-step reverse transcription-quantitative polymerase chain reaction assay for the detection of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) is an important disease that severely affects the swine industry and, therefore, warrants rapid and accurate diagnosis for its control. Despite the progress in developing diagnostic tools, including polymerase chain reaction (PCR)-based methods such as reverse transcription quantitative PCR (RT-qPCR) to diagnose PRRSV infection, its diagnosis at the genetic level is challenging because of its high genetic variability. Nevertheless, RT-qPCR is the easiest and fastest method for diagnosing PRRSV. Therefore, this study aimed to develop an RT-qPCR assay for rapid and accurate diagnosis of PRRSV by encompassing all publicly available PRRSV sequences. The developed assay using highly specific primers and probes could detect up to 10 copies of PRRSV-1 and -2 subtypes. Furthermore, a comparison of the performance of the developed assay with those of two commercial kits widely used in South Korea demonstrated the higher efficiency of the developed assay in detecting PRRSV infections in field samples. For PRRSV-1 detection, the developed assay showed a diagnostic agreement of 97.7% with the results of ORF5 sequencing, while for commercial kits, it showed 95.3% and 72.1% agreement. For PRRSV-2, the developed assay showed a diagnostic agreement of 97.7%, whereas the commercial kits showed 93% and 90.7% agreement. In conclusion, we developed an assay with higher accuracy than those of the tested commercial kits, which will contribute markedly to global PRRSV control.

Emergent Molecular Techniques Applied to the Detection of Porcine Viruses

Molecular diagnostic tests have evolved very rapidly in the field of human health, especially with the arrival of the recent pandemic caused by the SARS-CoV-2 virus. However, the animal sector is constantly neglected, even though accurate detection by molecular tools could represent economic advantages by preventing the spread of viruses. In this regard, the swine industry is of great interest. The main viruses that affect the swine industry are described in this review, including African swine fever virus (ASFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and porcine circovirus (PCV), which have been effectively detected by different molecular tools in recent times. Here, we describe the rationale of molecular techniques such as multiplex PCR, isothermal methods (LAMP, NASBA, RPA, and PSR) and novel methods such as CRISPR-Cas and microfluidics platforms. Successful molecular diagnostic developments are presented by highlighting their most important findings. Finally, we describe the barriers that hinder the large-scale development of affordable, accessible, rapid, and easy-to-use molecular diagnostic tests. The evolution of diagnostic techniques is critical to prevent the spread of viruses and the development of viral reservoirs in the swine industry that impact the possible development of future pandemics and the world economy.

Codon Pair Deoptimization (CPD)-Attenuated PRRSV-1 Vaccination Exhibit Immunity to Virulent PRRSV Challenge in Pigs

Commercially used porcine respiratory and reproductive syndrome (PRRS) modified live virus (MLV) vaccines provide limited protection with heterologous viruses, can revert back to a virulent form and they tend to recombine with circulating wild-type strains. Codon pair deoptimization (CPD) is an advanced method to attenuate a virus that overcomes the disadvantages of MLV vaccines and is effective in various virus vaccine models. The CPD vaccine against PRRSV-2 was successfully tested in our previous study. The co-existence of PRRSV-1 and -2 in the same herd demands protective immunity against both viruses. In this study, live attenuated PRRSV-1 was constructed by recoding 22 base pairs in the ORF7 gene of the E38 strain. The efficacy and safety of the CPD live attenuated vaccine E38-ORF7 CPD to protect against virulent PRRSV-1 were evaluated. Viral load, and respiratory and lung lesion scores were significantly reduced in animals vaccinated with E38-ORF7 CPD. Vaccinated animals were seropositive by 14 days post-vaccination with an increased level of interferon-γ secreting cells. In conclusion, the codon-pair-deoptimized vaccine was easily attenuated and displayed protective immunity against virulent heterologous PRRSV-1.

A recombinant porcine reproductive and respiratory syndrome virus type 2 field strain derived from two PRRSV-2-modified live virus vaccines

A porcine reproductive and respiratory syndrome virus (PRRSV) type 2 (PRRSV-2) isolate was obtained from lung samples collected from a 4.5-month-old pig at a wean-to-finish site in Indiana, USA, although no gross or microscopic lesions suggestive of PRRSV infection were observed in the lung tissue. Phylogenetic and molecular evolutionary analyses based on the obtained virus sequences indicated that PRRSV USA/IN105404/2021 was a natural recombinant isolate from Ingelvac PRRS® MLV and Prevacent® PRRS, which are PRRSV-2-modified live virus vaccines commercially available in the United States. This study is the first to report the detection of a PRRSV-2 recombinant strain consisting entirely of two modified live virus vaccine strains under field conditions. Based on clinical data and the absence of lung lesions, this PRRSV-2 recombinant strain was not virulent in swine, although its pathogenicity needs to be confirmed by clinical trials.

Optimized protocol for double vaccine immunization against classical swine fever and porcine reproductive and respiratory syndrome

BACKGROUND

Classical swine fever and porcine reproductive and respiratory syndrome have seriously affected the development of the swine breeding industry in China. Vaccine immunization remains the main way to prevent these infections. The aim of this study was to establish an optimized protocol for vaccine immunization against classical swine fever virus (CSFV) and porcine reproductive and respiratory syndrome virus (PRRSV).

METHODS

Blood samples were collected from the anterior vena cava of pigs after immunization, and blood indices, secreted levels of specific antibodies and neutralizing antibodies associated with humoral immunity, the proliferation capacity of T lymphocytes as a measure of cellular immunity, and secreted levels of IFN-γ and TNF-α were determined.

RESULTS

The results showed that simultaneous immunization against CSFV and PRRSV infections induced strong and specific humoral and T-cellular immune responses, high levels of cytokine IFN-γ secretion and delayed secretion of cytokine TNF-α. Moreover, significantly higher lymphocyte percentages and red blood cell and leukocyte counts were found in the group simultaneously immunized against CSFV and PRRSV. However, no statistically significant differences were observed in hemoglobin values, neutrophil counts, and median cell percentages among the S + PRRS, PRRS-S, and S-PRRS groups.

CONCLUSION

This study demonstrated that simultaneous immunization against CSFV and PRRSV had the advantages of inducing a rapid, enhanced, and long-lasting immune response. These findings provide a theoretical basis for the establishment of a reasonable and optimized vaccine immunization protocol against CSFV and PRRSV in combination with a variety of other vaccine inoculations.

Evaluating oral swab samples for PRRSV surveillance in weaning-age pigs under field conditions

Introduction

The use of serum and family oral fluids for porcine reproductive and respiratory syndrome virus (PRRSV) surveillance in weaning-age pigs has been previously characterized. Characterizing more sample types similarly offers veterinarians and producers additional validated sample options for PRRSV surveillance in this subpopulation of pigs. Oral swab sampling is relatively easy and convenient; however, there is sparse information on how it compares to the reference sample type for PRRSV surveillance under field conditions. Therefore, this study's objective was to compare the PRRSV reverse-transcription real-time polymerase chain reaction (RT-rtPCR) test outcomes of oral swabs (OS) and sera samples obtained from weaning-age pig litters.

Method

At an eligible breeding herd, six hundred twenty-three weaning-age piglets from 51 litters were each sampled for serum and OS and tested for PRRSV RNA by RT-rtPCR.

Results and Discussion

PRRSV RT-rtPCR positivity rate was higher in serum samples (24 of 51 litters, 83 of 623 pigs, with a mean cycle threshold (Ct) value of RT-rtPCR-positive samples per litter ranging from 18.9 to 32.0) compared to OS samples (15 of 51 litters, 33 of 623 pigs, with a mean Ct of RT-rtPCR positive samples per litter ranging from 28.2 to 36.9); this highlights the importance of interpreting negative RT-rtPCR results from OS samples with caution. Every litter with a positive PRRSV RT-rtPCR OS had at least one viremic piglet, highlighting the authenticity of positive PRRSV RT-rtPCR tests using OS; in other words, there was no evidence of environmental PRRSV RNA being detected in OS. Cohen's kappa analysis (Ck = 0.638) indicated a substantial agreement between both sample types for identifying the true PRRSV status of weaning-age pigs.

Signaling Lymphocytic Activation Molecule Family Member 1 Inhibits Porcine Reproductive and Respiratory Syndrome Virus Replication

The porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly contagious disease in domestic swine. Signaling lymphocytic activation molecule family member 1 (SLAMF1) is a costimulatory factor that is involved in innate immunity, inflammation, and infection. Here, we demonstrate that overexpression of the SLAMF1 gene inhibited PRRSV replication significantly and reduced the levels of key signaling pathways, including MyD88, RIG-I, TLR2, TRIF, and inflammatory factors IL-6, IL-1β, IL-8, TNF-β, TNF-α, and IFN-α in vitro. However, the knockdown of the SLAMF1 gene could enhance replication of the PRRSV and the levels of key signaling pathways and inflammatory factors. Overall, our results identify a new, to our knowledge, antagonist of the PRRSV, as well as a novel antagonistic mechanism evolved by inhibiting innate immunity and inflammation, providing a new reference and direction for PRRSV disease resistance breeding.

Extracellular Vesicles in Veterinary Medicine

Extracellular vesicles (EVs) are cell-derived membrane-bound vesicles involved in many physiological and pathological processes not only in humans but also in all the organisms of the eukaryotic and prokaryotic kingdoms. EV shedding constitutes a fundamental universal mechanism of intra-kingdom and inter-kingdom intercellular communication. A tremendous increase of interest in EVs has therefore grown in the last decades, mainly in humans, but progressively also in animals, parasites, and bacteria. With the present review, we aim to summarize the current status of the EV research on domestic and wild animals, analyzing the content of scientific literature, including approximately 220 papers published between 1984 and 2021. Critical aspects evidenced through the veterinarian EV literature are discussed. Then, specific subsections describe details regarding EVs in physiology and pathophysiology, as biomarkers, and in therapy and vaccines. Further, the wide area of research related to animal milk-derived EVs is also presented in brief. The numerous studies on EVs related to parasites and parasitic diseases are excluded, deserving further specific attention. The literature shows that EVs are becoming increasingly addressed in veterinary studies and standardization in protocols and procedures is mandatory, as in human research, to maximize the knowledge and the possibility to exploit these naturally produced nanoparticles.

Antiviral Effects of Heparan Sulfate Analogue‐Modified Two‐Dimensional MXene Nanocomposites on PRRSV and SARS‐CoV‐2

Due to the worldwide impact of viruses such as SARS‐CoV‐2, researchers have paid extensive attention to antiviral reagents against viruses. Despite extensive research on two‐dimensional (2D) transition metal carbides (MXenes) in the field of biomaterials, their antiviral effects have received little attention. In this work, heparan sulfate analogue (sodium 3‐mercapto‐1‐propanesulfonate, MPS) modified 2D MXene nanocomposites (Ti₃C₂‐Au‐MPS) for prevention of viral infection are prepared and investigated using severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pseudovirus and porcine reproductive and respiratory syndrome virus (PRRSV) as two model viruses. Ti₃C₂‐Au‐MPS nanocomposites are shown to possess antiviral properties in the different stages of PRRSV proliferation, such as direct interaction with PRRS virions and inhibiting their adsorption and penetration in the host cell. Additionally, Ti₃C₂‐Au‐MPS nanocomposites can strongly inhibit the infection of SARS‐CoV‐2 pseudovirus as shown by the contents of its reporter gene GFP and luciferase. These results demonstrate the potential broad‐spectrum antiviral property of Ti₃C₂‐Au‐MPS nanocomposites against viruses with the receptor of heparin sulfate. This work sheds light on the specific antiviral effects of MXene‐based nanocomposites against viruses and may facilitate further exploration of their antiviral applications.

Recent advances in the study of NADC34-like porcine reproductive and respiratory syndrome virus in China

Since porcine reproductive and respiratory syndrome virus (PRRSV) was first described in China in 1996, several genetically distinct strains of PRRSV have emerged with varying pathogenicity and severity, thereby making the prevention and control of PRRS more difficult in China and worldwide. Between 2017 and 2021, the detection rate of NADC34-like strain in China increased. To date, NADC34-like strains have spread to 10 Chinese provinces and have thus developed different degrees of pathogenicity and mortality. In this review, we summarize the history of NADC34-like strains in China and clarify the prevalence, genomic characteristics, restriction fragment length polymorphisms, recombination, pathogenicity, and vaccine status of this strain in China. In so doing, this study aims to provide a basis for the further development of prevention and control measures targeting the NADC34-like strain.

Porcine reproductive and respiratory virus 2 infection of the fetus results in multi-organ cell cycle suppression

Porcine reproductive and respiratory syndrome virus (PRRSV) infection during late gestation negatively affects fetal development. The objective of this study was to identify the fetal organs most severely impacted following infection, and evaluate the relationship between this response and fetal phenotypes. RNA was extracted from fetal heart, liver, lung, thymus, kidney, spleen, and loin muscle, collected following late gestation viral challenge of pregnant gilts. Initially, gene expression for three cell cycle promoters (CDK1, CDK2, CDK4) and one inhibitor (CDKN1A) were evaluated in biologically extreme phenotypic subsets including gestational age-matched controls (CON), uninfected (UNIF), high-viral load viable (HV-VIA), and high-viral load meconium-stained (HV-MEC) fetuses. There were no differences between CON and UNIF groups for any gene, indicating no impact of maternal infection alone. Relative to CON, high-viral load (HV-VIA, HV-MEC) fetuses showed significant downregulation of at least one CDK gene in all tissues except liver, while CDKN1A was upregulated in all tissues except muscle, with the heart and kidney most severely impacted. Subsequent evaluation of additional genes known to be upregulated following activation of P53 or TGFb/SMAD signaling cascades indicated neither pathway was responsible for the observed increase in CDKN1A. Finally, analysis of heart and kidney from a larger unselected population of infected fetuses from the same animal study showed that serum thyroxin and viral load were highly correlated with the expression of CDKN1A in both tissues. Collectively these results demonstrate the widespread suppression in cell division across all tissues in PRRSV infected fetuses and indicate a non-canonical regulatory mechanism.