Pathogenicity of two Chinese Seneca Valley virus (SVV) strains in pigs

Development of a VP2-based real-time fluorescent reverse transcription recombinase-aided amplification assay to rapidly detect Senecavirus A

Senecavirus A (SVA), a newly emergent picornavirus correlated with sudden neonatal mortality and vesicular lesions in pigs, has had a considerable impact on the global pig farming industry. Timely and dependable detection of SVA is helpful in preventing the further spread of this pathogenic virus. In the current study, a real-time fluorescent reverse transcription recombinase-aided amplification (rRT-RAA) assay, which targets the most conserved region within the VP2 gene of SVA, was developed and evaluated for SVA detection. The detection limit for this assay was tested to be 1.185 50% tissue culture infective dose (TCID₅₀ ) of SVA RNA per reaction at a 95% confidence interval, which is comparable to that of a previously published rRT-PCR assay for SVA. The testing results of the rRT-RAA assay were very reproducible and repeatable, with inter- and intra-assay coefficient of variation values less than 7.0%. In addition, the established rRT-RAA assay displayed excellent specificity for SVA detection without cross-reaction with other clinically important swine pathogenic viruses. The diagnostic performance of rRT-RAA was evaluated using 189 clinical swine samples, which were detected in parallel using the reference rRT-PCR assay. The results showed that 146 and 151 samples tested positive for SVA by rRT-RAA and rRT-PCR, respectively. The overall agreement between both assays was 97.4% (184/189) with a kappa value of 0.927 (p < .001). Further linear regression analysis demonstrated that the detection results between the two assays were significantly correlated (R² = 0.9192, p < .0001). Taken together, our newly established rRT-RAA assay is a powerful and time-saving diagnostic tool for SVA detection in clinical samples. This article is protected by copyright. All rights reserved.

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.

Identification of a B-Cell Epitope in the VP3 Protein of Senecavirus A

Senecavirus A (SVA) is a member of the genus Senecavirus of the family Picornaviridae. SVA-associated vesicular disease (SAVD) outbreaks have been extensively reported since 2014–2015. Characteristic symptoms include vesicular lesions on the snout and feet as well as lameness in adult pigs and even death in piglets. The capsid protein VP3, a structural protein of SVA, is involved in viral replication and genome packaging. Here, we developed and characterized a mouse monoclonal antibody (mAb) 3E9 against VP3. A motif ¹⁹²GWFSLHKLTK²⁰¹ was identified as the linear B-cell epitope recognized by mAb 3E9 by using a panel of GFP-tagged epitope polypeptides. Sequence alignments show that ¹⁹²GWFSLHKLTK²⁰¹ was highly conserved in all SVA strains. Subsequently, alanine (A)-scanning mutagenesis indicated that W193, F194, L196, and H197 were the critical residues recognized by mAb 3E9. Further investigation with indirect immunofluorescence assay indicated that the VP3 protein was present in the cytoplasm during SVA replication. In addition, the mAb 3E9 specifically immunoprecipitated the VP3 protein from SVA-infected cells. Taken together, our results indicate that mAb 3E9 could be a powerful tool to work on the function of the VP3 protein during virus infection.

Buffalo-Origin Seneca Valley Virus in China: First Report, Isolation, Genome Characterization, and Evolution Analysis

Pigs are the main host of Seneca Valley virus (SVV), previously known as Senecavirus A (SVA). Pigs affected by SVV have vesicles in the nose, hooves, and limp and may cause death in some severe cases. Occasionally, SVV has also been detected in mice, houseflies, environmental equipment, and corridors in pig farms. Moreover, it was successfully isolated from mouse tissue samples. In this study, an SVV strain (SVA/GD/China/2018) was isolated from a buffalo with mouth ulcers in the Guangdong province of China using seven mammalian cell lines (including BHK-21, NA, PK-15, ST, Vero, Marc-145, and MDBK). The genome of SVA/GD/China/2018 consists of 7,276 nucleotides. Multiple-sequence alignment showed that SVA/GD/China/2018 shared the highest nucleotide similarity (99.1%) with one wild boar-origin SVV strain (Sichuan HS-01) from the Sichuan province of China. Genetic analysis revealed that SVA/GD/China/2018 clustered with those porcine-origin SVV strains. To the best of our knowledge, this is the first report of SVV infection in buffalo, which might expand the host range of the virus. Surveillance should be expanded, and clinical significance of SVV needs to be further evaluated in cattle.

Pathogenicity of Seneca Valley virus in pigs and detection in Culicoides from an infected pig farm

Background

Porcine vesicular disease is caused by the Seneca Valley virus (SVV), it is a novel Picornaviridae, which is prevalent in several countries. However, the pathogenicity of SVV on 5–6 week old pigs and the transmission routes of SVV remain unknown.

Methods

This research mainly focuses on the pathogenicity of the CH-GX-01-2019 strain and the possible vector of SVV. In this study, 5–6 week old pigs infected with SVV (CH-GX-01-2019) and its clinical symptoms (including rectal temperatures and other clinical symptoms) were monitored, qRT-PCR were used to detect the viremia and virus distribution. Neutralization antibody assay was set up during this research. Mosquitoes and Culicoides were collected from pigsties after pigs challenge with SVV, and SVV detection within mosquitoes and Culicoides was done via RT-PCR.

Results

The challenged pigs presented with low fevers and mild lethargy on 5–8 days post infection. The viremia lasted more than 14 days. SVV was detected in almost all tissues on the 14th day following the challenge, and it was significantly higher in the hoofs (vesicles) and lymph nodes in comparison with other tissues. Neutralizing antibodies were also detected and could persist for more than 28 days, in addition neutralizing antibody titers ranged from 1:128 to 1:512. Mosquitoes and Culicoides were collected from the pigsty environments following SVV infection. Although SVV was not detected in the mosquitoes, it was present in the Culicoides, however SVV could not be isolated from the positive Culicoides.

Conclusions

Our work has enriched the knowledge relating to SVV pathogenicity and possible transmission routes, which may lay the foundation for further research into the prevention and control of this virus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01679-w.

N-Linked Glycosylation on Anthrax Toxin Receptor 1 Is Essential for Seneca Valley Virus Infection

Seneca Valley virus (SVV) is a picornavirus with potency in selectively infecting and lysing cancerous cells. The cellular receptor for SVV mediating the selective tropism for tumors is anthrax toxin receptor 1 (ANTXR1), a type I transmembrane protein expressed in tumors. Similar to other mammalian receptors, ANTXR1 has been shown to harbor N-linked glycosylation sites in its extracellular vWA domain. However, the exact role of ANTXR1 glycosylation on SVV attachment and cellular entry was unknown. Here we show that N-linked glycosylation in the ANTXR1 vWA domain is necessary for SVV attachment and entry. In our study, tandem mass spectrometry analysis of recombinant ANTXR1-Fc revealed the presence of complex glycans at N166, N184 in the vWA domain, and N81 in the Fc domain. Symmetry-expanded cryo-EM reconstruction of SVV-ANTXR1-Fc further validated the presence of N166 and N184 in the vWA domain. Cell blocking, co-immunoprecipitation, and plaque formation assays confirmed that deglycosylation of ANTXR1 prevents SVV attachment and subsequent entry. Overall, our results identified N-glycosylation in ANTXR1 as a necessary post-translational modification for establishing stable interactions with SVV. We anticipate our findings will aid in selecting patients for future cancer therapeutics, where screening for both ANTXR1 and its glycosylation could lead to an improved outcome from SVV therapy.

Isolation and evolutionary analysis of Senecavirus A isolates from Guangdong province, China

Senecavirus A (SVA), an emerging swine pathogen, has been reported in many provinces of China since the first outbreak in 2015 in Guangdong province. In this study, 10 lymph nodes positive for SVA, collected between 2018 and 2019 from slaughterhouses in Guangdong province, were subjected to virus isolation. Rapid and evident cytopathic effects (CPEs) were observed in SVA-infected PK-15 cells, including shrinking, rounding and detaching, with peak titers being reached at 24 h post infection (hpi). Electron microscopy showed that SVA particles are spherical and approximately 30 nm in diameter, and exist as crystalline lattices in cytoplasm revealed by ultra-thin sectioning. Phylogenetic analysis based on the whole genome sequences of all available isolates showed that SVA globally can be divided into two groups with each being further divided into two subgroups (Ia-b and IIa-b), and with the Guangdong isolates obtained here and other Chinese strains belonging to subgroups IIa and IIb. Evolutionary analysis showed that the mean substitution rate of SVA was 2.696 × 10^-3 per site per year based on whole genomic sequences, with subgroup IIb isolates having evolved faster than those of subgroup IIa. Analysis of efficient population size showed that the outbreak point of SVA worldwide occurred at the end of 2013 with that of subgroup IIb, the current dominant group, in mid 2014.

Infectious recombinant Senecavirus A expressing novel reporter proteins

Senecavirus A (SVA) is an emerging picornavirus that has been associated with vesicular disease and neonatal mortality in swine. The construction of SVA virus carrying foreign reporter gene provides a powerful tool in virus research. However, it is often fraught with rescuing a recombinant picornavirus harboring a foreign gene or maintaining the stability of foreign gene in the virus genome. Here, we successfully generated recombinant SVA GD05/2017 viruses (V-GD05-clone) expressing the green fluorescent protein (iLOV), red fluorescent protein (RFP), or NanoLuc luciferase (Nluc). These recombinant viruses have comparable growth kinetics to the parental virus. Genetic stability analysis indicated that V-GD05-iLOV was highly stable in retaining iLOV gene for more than 10 passages, while V-GD05-RFP and V-GD05-Nluc lost the foreign genes in five passages. In addition, high-intensity fluorescent signals were found in the V-GD05-RFP- and V-GD05-iLOV-infected cells by fluorescence observation and flow cytometry analysis, and the luciferase activity assay could quantitatively monitor the replication of V-GD05-Nluc. In order to identify the porcine cell receptor for SVA, anthrax toxin receptor 1 (ANTXR1) was knocked out or overexpressed in the ST-R cells. The ANTXR1 knock-out cells lost the ability for SVA infection, while overexpression of ANTXR1 significantly increased the cell permissivity. These results confirmed that ANTXR1 was the receptor for SVA to invade porcine cells as reported in the human cells. Overall, this study suggests that these SVA reporter viruses will be useful tools in elucidating virus pathogenesis and developing control measures. KEY POINTS: • We successfully generated SVA viruses expressing the iLOV, RFP, or Nluc. • The iLOV was genetically stable in the V-GD05-iLOV genome over ten passages. • ANTXR1 was the receptor for SVA to invade porcine cells.

Preliminary Evaluation of Protective Efficacy of Inactivated Senecavirus A on Pigs

Senecavirus A (SVA), formerly known as Seneca Valley virus (SVV), causes vesicular symptoms in adult pigs and acute death of neonatal piglets. This pathogen has emerged in major swine producing countries around the world and caused significant economic losses to the pig industry. Thus, it is necessary to develop strategies to prevent and control SVA infection. Herein, an SVA strain (named GD-ZYY02-2018) was isolated from a pig herd with vesicular symptoms in Guangdong province of China in 2018. The present study aimed to carry out the phylogenetic analysis of the GD-ZYY02-2018 strain, determine its pathogenicity in finishing pigs, and assess the protective efficacy of the inactivated GD-ZYY02-2018 strain against virus challenge. The results of phylogenetic analysis showed that the SVA GD-ZYY02-2018 strain belonged to the USA-like strains and had a close genetic relationship with recent Chinese SVA strains. Animal challenge experiment showed that 100-day-old pigs inoculated intranasally with SVA GD-ZYY02-2018 strain developed vesicular lesion, low fever, viremia, and virus shedding in feces. The immunization challenge experiment showed that pigs vaccinated with inactivated GD-ZYY02-2018 strain could produce a high titer of anti-SVA neutralizing antibody and no vesicular lesion, fever, viremia, and virus shedding in feces was observed in vaccinated pigs after challenge with GD-ZYY02-2018 strain, indicating that inactivated GD-ZYY02-2018 could protect finishing pigs against the challenge of homologous virus. In conclusion, preliminary results indicated that inactivated GD-ZYY02-2018 could be used as a candidate vaccine for in-depth research and might be conducive to the prevention and control of SVA infection.

A 5-Year Review of Senecavirus A in China since Its Emergence in 2015

Senecavirus A (SVA), previously known as Seneca Valley virus, is classified into the genus Senecavirus in the family Picornaviridae. This virus can cause vesicular disease and epidemic transient neonatal losses in swine. Typical clinical signs include vesicular and/or ulcerative lesions on the snout, oral mucosa, coronary bands and hooves. SVA emerged in Guangdong Province of China in 2015, and thereafter gradually spread into other provinces, autonomous regions and municipalities (P.A.M.s). Nowadays more than half of the P.A.M.s have been affected by SVA, and asymptomatic infection has occurred in some areas. The phylogenetic analysis shows that China isolates are clustered into five genetic branches, implying a fast evolutionary speed since SVA emergence in 2015. This review presented current knowledge concerning SVA infection in China, including its history, epidemiology, evolutionary characteristics, diagnostics and vaccines.

Transcriptome analysis of senecavirus A-infected cells: Type I interferon is a critical anti-viral factor

Senecavirus A (SVA)-associated vesicular disease (SAVD) has extensively been present in the swine industry during the past years. The mechanisms of SVA-host interactions at the molecular level, subsequent to SVA infection, are unclear. We studied the gene expression profiles of LLC-PK1 cells, with or without SVA infection, for 6 h and 12 h using an RNA-seq technology. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed on differentially expressed genes (DEGs). Immune-related genes and pathways were significantly modified after SVA infection. To confirm the RNA-seq data, 28 important DEGs were selected for RT-qPCR assays. All DEGs exhibited expression patterns consistent with the RNA-seq results. Among them, type I IFNs (including IFN-α and IFN-β) showed the largest upregulation, followed by RSAD2, DDX58, MX1 and the 17 other DEGs. In contrary, ID2 and another 5 DEGs were down-regulated or unchanged. These results indicated that type I IFNs play a critical role in host immune responses against SVA infection at early stage, while other immune-regulated genes directly or indirectly participate in the host immune responses.