First report and genetic characterization of Seneca Valley virus (SVV) in Chile

The construction and immunogenicity analyses of a recombinant pseudorabies virus with Senecavirus A VP3 protein co-expression

Senecavirus A (SVA)-associated porcine idiopathic vesicular disease (PIVD) and Pseudorabies (PR) are highly contagious swine disease that pose a significant threat to the global pig industry. In the absence of an effective commercial vaccine, outbreaks caused by SVA have occurred in many parts of the world. In this study, the PRV variant strain PRV-XJ was used as the parental strain to construct a recombinant PRV strain with the TK/gE/gI proteins deletion and the VP3 protein co-expression, named rPRV-XJ-ΔTK/gE/gI-VP3. The results revealed that PRV is a suitable viral live vector for VP3 protein expressing. As a vaccine, rPRV-XJ-ΔTK/gE/gI-VP3 is safe for mice, vaccination with it did not cause any clinical symptoms of PRV. Intranasal immunization with rPRV-XJ-ΔTK/gE/gI-VP3 induced strong cellular immune response and high levels of specific antibody against VP3 and gB and neutralizing antibodies against both PRV and SVA in mice. It provided 100% protection to mice against the challenge of virulent strain PRV-XJ, and alleviated the pathological lesion of heart and liver tissue in SVA infected mice. rPRV-XJ-ΔTK/gE/gI-VP3 appears to be a promising vaccine candidate against PRV and SVA for the control of the PRV variant and SVA.

A putative wild-type or wild-type-like hairpin structure is required within 3' untranslated region of Senecavirus A for virus replication

The 3' untranslated region (UTR) of Senecavirus A (SVA) was predicted to harbor two hairpin structures, hairpin-I and -II. The former is composed of two internal loops, one terminal loop and three stem regions; the latter comprises one internal loop, one terminal loop and two stem regions. In this study, we constructed a total of nine SVA cDNA clones, which contained different point mutations within a stem-formed motif in the hairpin-I or -II, for rescuing replication-competent viruses. Only three mutants were successfully rescued and moreover genetically stable during at least five serial passages. Computer-aided prediction showed these three mutants bearing either a wild-type or a wild-type-like hairpin-I in their individual 3' UTRs. Neither wild-type nor wild-type-like hairpin-I could be computationally predicted to exist in 3' UTRs of the other six unviable "viruses". The results suggested that the wild-type or wild-type-like hairpin-I was necessary in the 3' UTR for SVA replication.

Identification of cis-acting replication element in VP2-encoding region of Senecavirus A genome

Picornavirus possesses one positive-sense, single-stranded RNA genome, in which a cis-acting replication element (cre) is located. The cre is a stem-loop structure that harbors a conserved AAACA motif within its loop region. This motif functions as a template for adding two U residues to the viral VPg, therefore generating a VPg-pUpU that is required for viral RNA synthesis. Senecavirus A (SVA) is an emerging picornavirus. Its cre has not been identified as yet. In the present study, one putative cre containing a typical AAACA motif was computationally predicted to exist within the VP2-encoding sequence of SVA. To test the role of this putative cre, 22 SVA cDNA clones with different point mutations in their cre-formed sequences were constructed in an attempt to rescue replication-competent SVAs. A total of 11 viruses were rescued from their individual cDNA clones, implying that some mutated cres exerted lethal impacts on SVA replication. To eliminate these impacts, an intact cre was artificially inserted into those SVA cDNA clones without ability of recovering virus. The artificial cre was proven to be able of compensating for some, but not all, defects caused by mutated cres, leading to successful recovery of SVAs. These results indicated that the putative cre of SVA was functionally similar to those of other picornaviruses, perhaps involved in the uridylylation of VPg.

Translation of Senecavirus A polyprotein is initiated from the IRES-proximal initiation codon

To clarify whether Senecavirus A (SVA) has the potential of alternative translation, an extra G residue was inserted into an SVA cDNA clone, resultantly generating an "AUGAUG" motif. The second AUG is the authentic SVA initiation codon, whereas the first AUG is a putative one. Subsequently, eighteen nucleotides were inserted one by one between AUG and AUG for reconstructing cDNA clones. The test of virus recovery showed that three replication-competent SVAs, whose AUG/AUG-flanked sequences were not multiples of three nucleotides, were successfully rescued from their individual cDNA clones. The wild-type SVA possesses a UUUUU motif within the polyprotein-encoding region. Sanger sequencing showed that these three replication-competent SVAs harbored one or two extra U residues in the UUUUU motif, implying that polyprotein translation was initiated from the putative AUG, and the authentic AUG would be inactivated. This is probably attributed to the lack of ribosome scanning along an SVA genome.