Idiopathic Vesicular Disease Research Articles

Macrophage migration inhibitory factor facilitates replication of Senecavirus A by enhancing the glycolysis via hypoxia inducible factor 1 alpha

Senecavirus A (SVA) induced porcine idiopathic vesicular disease (PIVD) has been spread worldwide due to persistent infection, causing economic losses in swine industry. Host factors play an important role in replication of SVA, while, the interaction of migration inhibitory factor (MIF) and the virus has not been verified. Here, MIF facilitates the replication of SVA by enhancing the glycolysis via hypoxia-inducible factor alpha (HIF-1α) was reported. SVA infection up-regulates the expression of MIF in 3D4/21 cells, and infection experiment of cells with overexpression and interference expression of MIF showed that MIF facilitates the replication of SVA. MIF promoted the glycolysis in SVA infection to facilitate its replication by enhancing the accumulation of lactate and decreasing the production of adenosine triphosphate (ATP) and inhibiting the expression of retinoic acid-inducible gene I (RIG-I), mitochondrial antiviral-signaling protein (MAVS), interferon regulatory factor 3 (IRF3), interferon-beta (IFN-β), IFN-α, interferon-stimulating gene 15 (ISG15), and ISG56. Meanwhile, specific inhibitor verified MIF facilitates the replication of SVA by enhancing glycolysis. Further results showed MIF induces the increased expression of HIF-1α, which enhances MIF-induced glycolysis. These results provide new data on host factors in replication of SVA, as well as better understanding the role of MIF in virus infection.

Development of a CRISPR/Cas12a-based fluorescent detection method of Senecavirus A

BackgroundSenecavirus A (SVA), identified in 2002, is known to cause porcine idiopathic vesicular disease (PIVD), which presents with symptoms resembling other vesicular diseases. This similarity complicates field diagnosis. Conventional molecular diagnostic techniques are limited by their cost, sensitivity, and requirement for complicated instrumentation. Therefore, developing an effective and accurate diagnostic method is crucial for timely identification and isolation of affected pigs, thereby preventing further disease spread.MethodsIn this study, we developed a highly-specific and ultra-sensitive SVA detection method powered by CRISPR/Cas12a. To enhance the availability in laboratories with varied equipment conditions, microplate reader and ultraviolet light transilluminator were introduced. Moreover, PCR amplification has also been incorporated into this method to improve sensitivity. The specificity and sensitivity of this method were determined following the preparation of the recombinant Cas12a protein and optimization of the CRISPR/Cas12a-based trans-cleavage system.ResultsThe method demonstrated no cross-reactivity with ten kinds of viruses of swine. The minimum template concentration required to activate substantial trans-cleavage activity was determined to be 106 copies/µL of SVA templates. However, when PCR amplification was incorporated, the method achieved a detection limit of one copy of SVA templates per reaction. It also exhibited 100% accuracy in simulated sample testing. The complete testing process does not exceed three hours.ConclusionsImportantly, this method utilizes standard laboratory equipment, making it accessible for use in resource-limited settings and facilitating widespread and ultra-sensitive screening during epidemics. Overall, the development of this method not only broadens the array of tools available for detecting SVA but also holds significant promise for controlling the spread of PIVD.

Development and evaluation of inactivated vaccines incorporating a novel Senecavirus A strain-based Immunogen and various adjuvants in mice.

Porcine idiopathic vesicular disease (PIVD), one of several clinically indistinguishable vesicular diseases of pigs, is caused by the emerging pathogen Senecavirus A (SVA). Despite the widespread prevalence of porcine SVA infection, no effective commercial vaccines for PIVD prevention and control are available, due to high costs associated with vaccine testing in pigs, considerable SVA diversity, and SVA rapid evolution. In this study, SVA CH/JL/2022 (OP562896), a novel mutant SVA strain derived from an isolate obtained from a pig farm in Jilin Province, China, was inactivated then combined with four adjuvants, MONTANIDETM GEL02 PR (GEL 02), MONTANIDETM ISA 201 VG (ISA 201), MONTANIDETM IMG 1313 VG N (IMS1313), or Rehydragel LV (LV). The resulting inactivated SVA CH/JL/2022 vaccines were assessed for efficacy in mice and found to induce robust in vivo lymphocyte proliferation responses and strong IgG1, IgG2a, and neutralizing antibody responses with IgG2a/IgG1 ratios of <1. Furthermore, all vaccinated groups exhibited significantly higher levels of serum cytokines IL-2, IL-4, IL-6, and IFN as compared to unvaccinated mice. These results indicate that all vaccines elicited both Th1 and Th2 responses, with Th2 responses predominating. Moreover, vaccinated mice exhibited enhanced resistance to SVA infection, as evidenced by reduced viral RNA levels and SVA infection-induced histopathological changes. Collectively, our results demonstrate that the SVA-GEL vaccine induced more robust immunological responses in mice than did the other three vaccines, thus highlighting the potential of SVA-GEL to serve an effective tool for preventing and controlling SVA infection.

Experimental Seneca Valley virus infection in sows and their offspring

Neonatal mortality has been increasingly reported on swine breeding farms experiencing swine idiopathic vesicular disease (SIVD) outbreaks, which can be accompanied by lethargy, diarrhea, and neurologic signs in neonates. Seneca Valley Virus (SVV), or Senecavirus A, has been detected in clinical samples taken from pigs with SIVD. Experimental SVV inoculation has caused vesicular disease in pigs, particularly during the stages from weaning to finishing. However, it remains crucial to investigate whether SVV directly contributes to the increase in neonatal mortality rates. The following study was conducted to chronicle the pathogenesis of SVV infection in sows and their offspring. Ten sows were intranasally inoculated with 4.75 × 107 plaque-forming units of the virus per sow either late in gestation (n = 5) or within fourteen days of farrowing (n = 5). Each sow replicated SVV following intranasal inoculation, but only one out of ten sows developed a vesicular lesion on the snout. Evidence of transplacental infection was observed in two litters, and an additional two litters became infected following parturition out of five litters from sows inoculated in late gestation. No clinical signs were observed in the infected neonates. Likewise, no clinical signs were observed in the other five litters inoculated after farrowing, although each piglet did replicate the challenge virus. In this study, the experimental challenge of SVV did not result in neonatal mortality in contrast to observations in the field; however, it has shed light on the pathogenesis of the virus, the transmission of SVV between sows and their offspring, and host immune response that can help shape control measures in the field.

Senecavirus A-induced glycolysis facilitates virus replication by promoting lactate production that attenuates the interaction between MAVS and RIG-I

Senecavirus A (SVA)-induced porcine idiopathic vesicular disease has caused huge economic losses worldwide. Glucose metabolism in the host cell is essential for SVA proliferation; however, the impact of the virus on glucose metabolism in host cells and the subsequent effects are still unknown. Here, glycolysis induced by SVA is shown to facilitate virus replication by promoting lactate production, which then attenuates the interaction between the mitochondrial antiviral-signaling protein (MAVS) and retinoic acid-inducible gene I (RIG-I). SVA induces glycolysis in PK-15 cells, as indicated by significantly increased expression of hexokinase 2 (HK2), 6-phosphofructokinase (PFKM), pyruvate kinase M (PKM), phosphoglycerate kinase 1 (PGK1), hypoxia-inducible factor-1 alpha (HIF-1α), and superoxide dismutase-2 (SOD2) in a dose-and replication-dependent manner, and enhanced lactate production, while reducing ATP generation. Overexpression of PKM, PGK1, HIF-1α, and PDK3 in PK-15 cells and high glucose concentrations promote SVA replication, while glycolytic inhibitors decrease it. Inhibition of RLR signaling allowed better replication of SVA by promoting lactate production to attenuate the interaction between MAVS and RIG-I, and regulatory effect of glycolysis on replication of SVA was mainly via RIG-I signaling. SVA infection in mice increased expression of PKM and PGK1 in tissues and serum yields of lactate. Mice treated with high glucose and administered sodium lactate showed elevated lactate levels and better SVA replication, as well as suppressed induction of RIG-I, interferon beta (IFNβ), IFNα, interferon-stimulated gene 15 (ISG15), and interleukin 6 (IL-6). The inhibitory effect on interferons was lower in mice administered sodium oxamate and low glucose compared to the high glucose, indicating that RLR signaling was inhibited by SVA infection through lactate in vitro and in vivo. These results provide a new perspective on the relationship between metabolism and innate immunity of the host in SVA infection, suggesting that glycolysis or lactate may be new targets against the virus.

LncRNA 8244-ssc-miR-320-CCR7 Regulates IFN-β during SVA Infecting PK-15 Cells.

Seneca Valley virus (SVV), a member of the Picornaviridae family, is an oncolytic RNA virus that can cause idiopathic vesicular disease and increase mortality in newborn piglets. Although research on the pathogenic characteristics, epidemiology, pathogenic mechanism, and clinical diagnosis of SVA has increased due to its emergence and prevalence, the interaction between SVA and its host lncRNA has not been fully studied. This study used qualcomm sequencing to analyze differentially expressed lncRNAs and found that during SVA infection, lncRNA 8244 was significantly down-regulated in both PK-15 cells and piglets. Further analysis through quantitative real-time PCR and dual luciferase experiments demonstrated that lncRNA8244 could compete with ssc-miR-320 to regulate the expression of CCR7. The lncRNA824-ssc-miR-320-CCR7 axis activated the TLR-mediated signaling pathway, which recognized viral molecules and induced the expression of IFN-β. These findings provide new insight into the interaction between lncRNA and SVA infection, which could lead to a better understanding of SVA pathogenesis and contribute to the prevention and control of SVA disease.

Development of an indirect ELISA using a novel linear epitope at the C-terminal region of the VP2 protein to specifically detect antibodies against Senecavirus A

BackgroundSenecavirus A (SVA) is a pathogen that has recently caused porcine idiopathic vesicular disease (PIVD). The clinical signs are similar to those of foot-and-mouth disease, porcine vesicular disease, and vesicular stomatitis. Therefore, identification of SVA as a cause of PIVD is important to eliminate this emerging pathogen.MethodsIn this study, an indirect ELISA based on the VP2 epitope (VP2-epitp-ELISA) was developed to detect antibodies directed against SVA.ResultsA novel linear epitope (271GLRNRFTTGTDEEQ284) was first identified at the C-terminus of the VP2 protein by epitope mapping. The diagnostic performance of VP2-epitp-ELISA was estimated by testing a panel of known background sera from swine. Under the optimum test conditions, when the cutoff value was 37%, the diagnostic sensitivity (Dn) and diagnostic specificity (Dp) of the assay were 91.13% and 91.17%, respectively. The accuracy of VP2-epitp-ELISA was validated and further compared with that of commercial diagnostic kits. The diagnostic results showed that VP2-epitp-ELISA did not cross-react with serum positive for other idiopathic vesicular diseases and had a concordance rate of 90.41% with the Swinecheck® SVA bELISA.ConclusionsThese results indicate that VP2-epitp-ELISA is suitable for specific detection of antibodies against SVA in swine.

Seneca Valley Virus Induces DHX30 Cleavage to Antagonize Its Antiviral Effects.

Seneca Valley virus (SVV) is a new pathogen associated with porcine idiopathic vesicular disease (PIVD) in recent years. However, SVV-host interaction is still unclear. In this study, through LC-MS/MS analysis and coimmunoprecipitation analysis, DHX30 was identified as a 3Cpro-interacting protein. 3Cpro mediated the cleavage of DHX30 at a specific site, which depends on its protease activity. Further study showed that DHX30 was an intrinsic antiviral factor against SVV that was dependent on its helicase activity. DHX30 functioned as a viral-RNA binding protein that inhibited SVV replication at the early stage of viral infection. RIP-seq showed comparatively higher coverage depth at SVV 5'UTR, but the distribution across SVV RNA suggested that the interaction had low specificity. DHX30 expression strongly inhibited double-stranded RNA (dsRNA) production. Interestingly, DHX30 was determined to interact with 3D in an SVV RNA-dependent manner. Thus, DHX30 negatively regulated SVV propagation by blocking viral RNA synthesis, presumably by participating in the viral replication complex. IMPORTANCE DHX30, an RNA helicase, is identified as a 3Cpro-interacting protein regulating Seneca Valley virus (SVV) replication dependent on its helicase activity. DHX30 functioned as a viral-RNA binding protein that inhibited SVV replication at the early stage of virus infection. DHX30 expression strongly inhibited double-stranded RNA (dsRNA) production. In addition, 3Cpro abolished DHX30 antiviral effects by inducing DHX30 cleavage. Thus, DHX30 is an intrinsic antiviral factor that inhibits SVV replication.

Evaluation of Immunoreactivity and Protection Efficacy of Seneca Valley Virus Inactivated Vaccine in Finishing Pigs Based on Screening of Inactivated Agents and Adjuvants.

Seneca Valley virus (SVV), also known as Senecavirus A (SVA), is a non-enveloped and single-strand positive-sense RNA virus, which belongs to the genus of Senecavirus within the family Picornaviridae. Porcine idiopathic vesicular disease (PIVD) caused by SVV has frequently been prevalent in America and Southeast Asia (especially in China) since the end of 2014, and has caused continuing issues. In this study, an SVV strain isolated in China, named SVV LNSY01-2017 (MH064435), was used as the stock virus for the preparation of an SVV-inactivated vaccine. The SVV culture was directly inactivated using binary ethyleneimine (BEI) and β-propiolactone (BPL). BPL showed a better effect as an SVV inactivator, according to the results of pH variation, inactivation kinetics, and the detection of VP1 content during inactivation. Then, SVV inactivated by BPL was subsequently emulsified using different adjuvants, including MONTANIDETM ISA 201 VG (ISA 201) and MONTANIDETM IMG 1313 VG N (IMS 1313). The immunoreactivity and protection efficacy of the inactivated vaccines were then evaluated in finishing pigs. SVV-BPL-1313 showed a better humoral response post-immunization and further challenge tests post-immunization showed that both the SVV-BPL-201 and SVV-BPL-1313 combinations could resist challenge from a virulent SVV strain. The SVV LNSY01-2017-inactivated vaccine candidate developed here represents a promising alternative to prevent and control SVV infection in swine.

Suppressor of cytokine signaling 1 (SOCS1) inhibits antiviral responses to facilitate Senecavirus A infection by regulating the NF-κB signaling pathway

Senecavirus A (SVA) is a new virus inducing porcine idiopathic vesicular disease that causes significant economic losses. Although some progress has been made in etiological research, the role of host factors in SVA infection remains unclear. This study investigated the role of the host factor, suppressor of cytokine signaling 1 (SOCS1), in SVA infection. The expression of SOCS1 was significantly upregulated with infection of SVA in a dose-dependent manner, and SOCS1 inhibited the expression of type I interferons (IFN-α, IFN-β) and the production of interferon stimulating genes (ISGs) (ISG56, ISG54, PKR), thereby facilitating viral replication. Further results showed that inhibition of antiviral responses of SOCS1 was achieved by regulating the NF-κB signaling pathway, which attenuates the production of IFNs and pro-inflammatory cytokines. These findings provide a new perspective of SVA pathogenesis and may partially explain the persistence of this infection. Moreover, the data indicate that targeting SOCS1 can help in developing new agents against SVA infection.

Global Phosphoproteomics Analysis of IBRS-2 Cells Infected With Senecavirus A.

Phosphorylation is a widespread posttranslational modification that regulates numerous biological processes. Viruses can alter the physiological activities of host cells to promote virus particle replication, and manipulating phosphorylation is one of the mechanisms. Senecavirus A (SVA) is the causative agent of porcine idiopathic vesicular disease. Although numerous studies on SVA have been performed, comprehensive phosphoproteomics analysis of SVA infection is lacking. The present study performed a quantitative mass spectrometry-based phosphoproteomics survey of SVA infection in Instituto Biologico-Rim Suino-2 (IBRS-2) cells. Three parallel experiments were performed, and 4,520 phosphosites were quantified on 2,084 proteins. Gene Ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses showed that many phosphorylated proteins were involved in apoptosis and spliceosome pathways, and subcellular structure localization analysis revealed that more than half were located in the nucleus. Motif analysis of proteins with differentially regulated phosphosites showed that proline, aspartic acid, and glutamic acid were the most abundant residues in the serine motif, while proline and arginine were the most abundant in the threonine motif. Forty phosphosites on 27 proteins were validated by parallel reaction monitoring (PRM) phosphoproteomics, and 30 phosphosites in 21 proteins were verified. Nine proteins with significantly altered phosphosites were further discussed, and eight [SRRM2, CDK13, DDX20, DDX21, BAD, ELAVL1, PDZ-binding kinase (PBK), and STAT3] may play a role in SVA infection. Finally, kinase activity prediction showed 10 kinases’ activity was reversed following SVA infection. It is the first phosphoproteomics analysis of SVA infection of IBRS-2 cells, and the results greatly expand our knowledge of SVA infection. The findings provide a basis for studying the interactions of other picornaviruses and their mammalian host cells.

Evaluation of immunogenicity and protective efficacy of a novel Senecavirus A strain-based inactivated vaccine in mice

Senecavirus A (SVA) is an emerging picornavirus associated with porcine idiopathic vesicular disease (PIVD), which is clinically indistinguishable from foot-and-mouth disease and other vesicular diseases in pigs. In recent years, the wide spread of SVA has caused huge economic losses to the world's pig industry. However, there are no vaccines currently available to prevent and control the infection of SVA due to the extensive diversity of SVA isolates and high cost of the pig model for vaccine evaluation. In the present study, a novel SVA CH-HNCY-2019 strain with unique amino-acid mutations in VP1, VP3 and 3C was isolated from the central part of China. A mouse model was proposed to for evaluation of the immunogenicity and protective efficacy of the inactivated CH-HNCY-2019 vaccine. The results indicated that one dose immunization of 107TCID50 inactivated CH-HNCY-2019 vaccine in mice induced a high titer of neutralizing antibody and complete protection. After challenging with the homologous virus, no viral RNA or histopathological damages were detected in the heart, liver, spleen, lung, kidney, intestine and brain tissues of the immunized mice. However, viral RNA and different degrees of histopathological damages were observed in all corresponding tissues of the unimmunized mice. In summary, the present study proved that mouse is a candidate animal model for the primary evaluation of the immunogenicity and protection efficacy of SVA vaccines for the first time. In addition, the inactivated SVA CH-HNCY-2019 vaccine was immunogenic and could protect mice against homologous viral challenges.

Seneca Valley virus 3Cpro degrades heterogeneous nuclear ribonucleoprotein A1 to facilitate viral replication

ABSTRACT Seneca Valley virus (SVV) is a recently-identified important pathogen that is closely related to idiopathic vesicular disease in swine. Infection of SVV has been shown to induce a variety of cellular factors and their activations are essential for viral replication, but whether heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) involved in SVV replication is unknown. The cytoplasmic redistribution of hnRNP A1 is considered to play an important role in the virus life cycle. Here, we demonstrated that SVV infection can promote redistribution of the nucleocytoplasmic shuttling RNA-binding protein hnRNP A1 to the cytoplasm from the nucleus, whereas hnRNP A1 remained mainly in the nucleus of mock-infected cells. siRNA-mediated knockdown of the gene encoding hnRNP A1 attenuated viral replication as evidenced by decreased viral protein expression and virus production, whereas its overexpression enhanced replication. Moreover, infection with SVV induced the degradation of hnRNP A1, and viral 3 C protease (3 Cpro) was found to be responsible for its degradation and translocation. Further studies demonstrated that 3 Cpro induced hnRNP A1 degradation through its protease activity, via the proteasome pathway. This degradation could be attenuated by a proteasome inhibitor (MG132) and inactivation of the conserved catalytic box in 3 Cpro. Taken together, these results presented here reveal that SVV 3 C protease targets cellular hnRNP A1 for its degradation and translocation, which is utilized by SVV to aid viral replication, thereby highlighting the control potential of strategies for infection of SVV.

Comparison of historical and contemporary isolates of Senecavirus A

Senecavirus A (SVA) was discovered as a cell culture contaminant in 2002, and multiple attempts to experimentally reproduce disease were unsuccessful. Field reports of porcine idiopathic vesicular disease (PIVD) cases testing PCR positive for SVA in addition to outbreaks of PIVD in Brazil and the United States in 2015 suggested SVA was a causative agent, which has now been consistently demonstrated experimentally. Ease of experimental reproduction of disease with contemporary strains of SVA raised questions concerning the difficulty of reproducing vesicular disease with historical isolates. The following study was conducted to compare the pathogenicity of SVA between historical and contemporary isolates in growing pigs. Six groups of pigs (n = 8) were intranasally inoculated with the following SVA isolates: SVV001/2002, CAN/2011, HI/2012, IA/2015, NC/2015, SD/2015. All isolates induced vesicular disease in at least half of the inoculated pigs from each group. All pigs replicated virus as demonstrated by serum and/or swab samples positive for SVA by quantitative PCR. Pig sera tested by virus neutralization assay demonstrated cross-neutralizing antibodies against all viruses utilized in the study. Cross-neutralizing antibodies from pigs inoculated with historical isolates were lower than those pigs that were inoculated with contemporary isolates. Phylogenetic analysis revealed two clades with SVV001/2002 being in a separate clade compared to the other five isolates. Although differences in the infection kinetics and sequences of these six isolates were found, clinical presentation of vesicular disease was similar between both historical and contemporary isolates.

Eradication of Swine Vesicular Disease in Italy.

Swine vesicular disease (SVD) is a contagious viral disease of pigs clinically indistinguishable from other vesicular diseases, such as foot and mouth disease, vesicular stomatitis, vesicular exanthema of swine, and idiopathic vesicular disease. In Italy, where SVD was first reported in 1966, an eradication program started in 1995. The program, updated in 2008, was based on regionalization, complete control on pig movements, improvement of pig farms biosecurity, appropriate cleansing and disinfection procedures of vehicles approved for pig transportation, and a testing program using both serological and virological assays. In cases of confirmed SVD virus infection a stamping-out policy was applied. In the period 2009 to 2019, between 300,000 and 400,000 pigs were serologically tested each year. The last SVD outbreak was notified in 2015, and the last seropositive pig was detected in 2017. SVD surveillance is still ongoing and no proof of virus activity has been detected so far. All available data support the complete SVD virus eradication from the Italian pig industry.

Genetic evolution and epidemiological analysis of Seneca Valley virus (SVV) in China

Seneca Valley virus (SVV) is a novel Picornaviridae that is closely associated with porcine idiopathic vesicular disease (PIVD). Here, a novel SVV strain (CH-GX-01-2019) was detected and isolated from swine in Guangxi Province, China. The complete genomic sequence of CH-GX-01-2019 exhibited 93.3–98.9 % identify with other SVV isolates at the nucleotide level. CH-GX-01-2019 showed the highest level of similarity (98.9 %) with Vietnamese strains. And CH-GX-01-2019 exhibited two consecutive amino acid mutations in VP1 gene. Phylogenetic analysis based on the complete genome and the VP1 gene showed that Chinese SVV isolates can be divided into three clusters. We analyzed the geographical distributions of SVV strains in China and found that the epidemiology of SVV in China is complicated; most strains are distributed predominantly in south and central China. Between 2015 and 2019, the dominant epidemic SVV isolates in China have changed from clusters 1 and 3 to cluster 2. CH-GX-01-2019 (cluster 3) is a recombinant strain from Colombia-2016 (cluster 2) and HB-CH-2016 (cluster 1). Our findings will enhance our understanding of the prevalence and genetic variation of SVV in the swine herds of China and provide important insights into the molecular epidemiology of SVV.

Potent Protective Immune Responses to Senecavirus Induced by Virus-Like Particle Vaccine in Pigs.

Senecavirus A (SVA) is the pathogen that has recently caused porcine idiopathic vesicular disease (PIVD). The clinical symptoms of PIVD are similar to those of acute foot-and-mouth disease and also can result in the death of newborn piglets, thus entailing economic losses. Vaccine immunization is the most effective way to prevent and control SVA. Among all SVA vaccines reported, only the SVA inactivated vaccine has been successfully developed. However, to ensure the elimination of this pathogen, safer and more effective vaccines are urgently required. A virus-like particles (VLPs)-based vaccine is probably the best alternative to inactivated vaccine. To develop an SVA VLPs vaccine and evaluate its immune effect, a prokaryotic expression system was used to produce SVA capsid protein and assemble VLPs. The VLPs were characterized by affinity chromatography, sucrose density gradient centrifugation, ZetaSizer and transmission electron microscopy. Meanwhile, the SVA CH-HB-2017 strain was used to infect pigs and to determine infection routes and dose. Experimental pigs were then immunized with the SVA VLPs vaccine emulsified in an ISA 201 adjuvant. The results showed that the VLPs vaccine induced neutralizing and specific antibodies at similar levels as an inactivated SVA vaccine after immunization. The level of INF-γ induced by the VLPs vaccine gradually decreased—similar to that of inactivated vaccine. These results indicated that VLPs vaccine may simultaneously cause both cellular and humoral immune responses. Importantly, after the challenge, the VLPs vaccine provided similar levels of protection as the inactivated SVA vaccine. In this study, we successfully obtained novel SVA VLPs and confirmed their highly immunogenicity, thus providing a superior candidate vaccine for defense and elimination of SVA, compared to the inactivated vaccine.

Development of an improved dual-promoter-based reverse genetics system for emerging Senecavirus A

Senecavirus A (SVA), a recently emerging picornavirus, poses a great threat to the swine industry because it causes swine idiopathic vesicular disease and epidemic transient neonatal losses. Thus far, the progress in SVA viral pathogenesis studies and vaccine development remains sluggish, and an available and convenient reverse genetics system would undoubtedly promote relevant research. Herein, we established an improved universal dual-promoter reverse genetics system with an SVA-specific hammerhead ribozyme and hepatitis delta virus ribozyme at both terminals of the viral genome; this system could be applied to rescue all SVA strains by both eukaryotic and prokaryotic RNA polymerase systems. The genome of the clone-derived Chinese field strain CH/HeN-2018 was assembled into the universal vector pcDNA-rSVAuni through the Gibson assembly technique. Moreover, two silent mutations, G6848C and C7163 G, were separately engineered into the full-length cDNA clone with one step site-directed mutagenesis to create a KpnI restriction enzyme site, which served as a unique genetic marker. The viruses, designated rCH/HeN-2018-T7, rCH/HeN-2018-CMV, rCH/HeN-2018-6484 m and rCH/HeN-2018-7163 m, were successfully rescued through both CMV- and T7-dependent pathways, and their biological properties were further evaluated. The results showed that all four viruses grew rapidly in PK-15 cells and exhibited viral titers and growth kinetics similar to those of parental wtCH/HeN-2018. The established reverse genetics system is easily operated and can be applied to rescue all SVA strains in a short time, which will be helpful for studying SVA biology, including viral pathogenesis, antiviral therapies and vaccine development.

Genomic diversity and recombination of Seneca Valley viruses emerged in pig herds in Guangdong Province during 2019.

Seneca Valley virus (SVV) is an emerging global picornavirus that causes porcine idiopathic vesicular disease. We characterized the genome and conducted evolutionary and recombination analyses of four newly identified SVV strains which were CH-GDZS-2019, CH-GDMZ-2019, CH-GDHZ01-2019, and CH-GDHZ02-2019. Sequence alignment and phylogenetic analysis showed that strains circulating in swine herds in China were genetically diverse and complex. Recombination analyses indicated that strain CH-GDZS-2019 was derived from strains USA-IA44662-2015-P1 and USA-GBI29-2015, which were both isolated in the USA in 2015, while CH-GDMZ-2019 was derived from the Chinese field strains 1-2018-BH-China and CH-GDQC-2017. Our results provided important insights into the molecular characterization of the SVV strains co-circulating in Guangdong Province in China in 2019 and demonstrated the importance of additional SVV surveillance in China.

Comparison of the Pathogenicity of Two Different Branches of Senecavirus a Strain in China.

Senecavirus A (SVA), an emerging infectious disease, is associated with the porcine idiopathic vesicular disease. Here, the pathogenesis of different strains of SVA was investigated in growing-finishing pigs. We aimed to evaluate the replication characteristics, virus particle morphology, clinical signs, and vesicular lesions in comparison with two different strains of SVA. The animals were infected with SVA HB-CH-2016 or CH/AH-02/2017 by intranasal routes (3 mL, 109TCID50/mL) and monitored daily for 14 days post-inoculation (dpi) for clinical signs and vesicular lesions. Viremia or viral shedding was detected in the blood, fecal swab, and nasal swab samples. Results showed no distinct differences in plaque size, replication ability, and characteristic virions between SVA HB-CH-2016 and CH/AH-02/2017 strains. Animal experimental results showed that both SVA CH/AH-02/2017 and SVA HB-CH-2016 could infect pigs. However, an obvious difference in the pathogenicity and dynamics of infection was observed between SVA HB-CH-2016 and CH/AH-02/2017 strains. The pathogenesis of SVA CH/AH-02/2017 was similar to that of published results of USA strains, whereas the SVA HB-CH-2016 strain had low pathogenicity to pigs. Clinical signs and vesicular lesions were observed in SVA CH/AH-02/2017-infected pigs. Additionally, the different branches of SVA should be capable of inducing broad cross-reactive neutralizing antibodies, which play an important role in clearing the SVA virus. This study of animal models for SVA infection will be beneficial to develop vaccines and antivirals.