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

Genomic profile of eGFP-tagged senecavirus A subjected to serial plaque-to-plaque transfers

Senecavirus A (SVA) belongs to the genus Senecavirus in the family Picornaviridae. This virus possesses a positive-sense, single-stranded RNA genome, approximately 7200 nt in length, composed of a single 5' untranslated region, encoding region and 3' untranslated region. In this study, a recombinant SVA tagged with enhanced green fluorescent protein (eGFP) sequence, rSVA-eGFP, was rescued from its cDNA clone using reverse genetics. The passage-5 (P5) rSVA-eGFP was totally subjected to 55 rounds of consecutive fluorescent plaque-to-fluorescent plaque (FP-FP) transfers, and one extra common passaging in vitro. The P61 viral stock was analyzed by next-generation sequencing. The result showed ten single-nucleotide mutations (SNMs) in the rSVA-eGFP genome, including nine transitions and only one transversion. The P61 progeny still showed a complete eGFP sequence, indicating no occurrence of copy-choice recombination within the eGFP region during serial FP-FP transfers. In other words, this progeny was genetically deficient in the recombination of eGFP sequence (RES), namely, an RES-deficient strain. Out of ten SNMs, three were missense mutations, leading to single-amino acid mutations (SAAMs): F15V in L protein, A74T in VP2, and E53R in 3D protein. The E53R was predicted to be spatially adjacent to the RNA channel of 3D protein, perhaps involved in the emergence of RES-deficient strain. In conclusion, this study uncovered a global landscape of rSVA-eGFP genome after serial FP-FP transfers, and moreover shed light on a putative SAAM possibly related to the RES-deficient mechanism.

Real-time detection of Seneca Valley virus by one-tube RPA-CRISPR/Cas12a assay

Introduction

Senecavirus A (SVA) is a highly contagious virus that causes vesicular disease in pigs. At present, laboratory detection methods, such as virus isolation and polymerase chain reaction (PCR), required precision instruments and qualified personnel, making them unsuitable for point-of-care tests (POCT). Fortunately, the emergence of CRISPR/Cas system has provided new opportunities for fast and efficient pathogen detection.

Methods

This study successfully developed a precise and sensitive detection platform for diagnosing SVA by combining the CRISPR system with recombinase polymerase amplification (RPA).

Results

The minimum detection limit of the assay was 10 copies of the SVA genome. Meanwhile, the assay demonstrated high specificity. To validate the effectiveness of this system, we tested 85 swine clinical samples and found that the fluorescence method had a 100% coincidence rate compared to RT-qPCR.

Discussion

Overall, the RPA-CRISPR/Cas12a assay established in our study is a highly effective method for detecting SVA and holds great potential for practical applications in the resource-limited settings.

Identification of new conserved linear B-cell epitopes in the 3AB and 3C protein of Senecavirus A

Senecavirus A (SVA) is a member of the Picornaviridae family, Senecavirus genus. The outbreak of swine vesicular disease caused by SVA has presented a significant threat to pig husbandry and public health, resulting in substantial economic losses. In this study, recombinant SVA 3AB and 3C proteins were expressed in the prokaryotic system, purified, and utilized to generate eight monoclonal antibodies (mAbs) specific to SVA 3AB or 3C proteins. Three B-cell epitopes recognized by these mAbs were subsequently identified by Western blotting. The mAbs 3G3, 3D6, and 3B7 against 3AB recognize the epitope ⁹⁰NAYDGPKKNS¹⁰⁰; the mAbs 2C10, 2C8, and 2D12 against 3C recognize the epitope ⁷⁵FTHHGLPTDL⁸⁵, and the mAbs 3C4 and 4A11 against 3C recognize the epitope ⁹⁵DQMPARNSRV¹⁰⁵. Moreover, all three epitopes are highly conserved in different SVA strains and are exposed on the surface of 3AB or 3C proteins, potentially representing important B-cell epitopes. This study constitutes the first report of SVA nonstructural protein epitopes, which may be beneficial for developing innovative detection methods and vaccines and for investigating the roles of 3AB and 3C in viral replication.

The Establishment and Application of Indirect 3AB-ELISA for The Detection of Antibodies against Senecavirus A

Senecavirus A (SVA) is an emerging pathogen that negatively affects the pig industry in China. Affected animals present vesicular lesions which are indistinguishable from other vesicular diseases. To date, there is no commercial vaccine that can be used to control SVA infection in China. In this study, recombinant SVA 3AB, 2C, 3C, 3D, L and VP1 proteins are expressed by using a prokaryotic expression system. The kinetics of the presence and levels of SVA antibodies with SVA-inoculated pig serum show that 3AB has the best antigenicity. An indirect enzyme-linked immunosorbent assay (ELISA) is developed with the 3AB protein, exhibiting a sensitivity of 91.3% and no cross-reaction with serum antibodies against PRRSV, CSFV, PRV, PCV2 or O-type FMDV. Given the high sensitivity and specificity of this approach, a nine-year (2014–2022) retrospective and prospective serological study is conducted to determine the epidemiological profile and dynamics of SVA in East China. Although SVA seropositivity declined markedly from 2016 (98.85%) to 2022 (62.40%), SVA transmission continues in China. Consequently, the SVA 3AB-based indirect ELISA has good sensitivity and specificity and is suitable for viral detection, field surveillance and epidemiological studies.