Senecavirus A (SVA) is a picornavirus that causes vesicular disease in swine and the only member of the Senecavirus genus. Like in all members of Picornaviridae, the 5′ untranslated region (5’UTR) of SVA contains an internal ribosome entry site (IRES) that initiates cap-independent translation. For example, the replacement of the IRES of foot-and-mouth disease virus (FMDV) with its relative bovine rhinitis B virus (BRBV) affects the viral translation efficiency and virulence. Structurally, the IRES from SVA resembles that of hepatitis C virus (HCV), a flavivirus. Given the roles of the IRES in cap-independent translation for picornaviruses, we sought to functionally characterize the IRES of this genus by studying chimeric viruses generated by exchanging the native SVA IRES with that of HCV either entirely or individual domains. First, the results showed that a chimeric SVA virus harboring the IRES from HCV, H-SVA, is viable and replicated normally in rodent-derived BHK-21 cells but displays replication defects in porcine-derived ST cells. In the generation of chimeric viruses in which domain-specific elements from SVA were replaced with those of HCV, we identified an essential role for the stem-loop I element for IRES activity and recombinant virus recovery. Furthermore, a series of stem-loop I mutants allowed us to functionally characterize discrete IRES regions and correlate impaired IRES activities, using reporter systems with our inability to recover recombinant viruses in two different cell types. Interestingly, mutant viruses harboring partially defective IRES were viable. However, no discernable replication differences were observed, relative to the wild-type virus, suggesting the cooperation of additional factors, such as intermolecular viral RNA interactions, act in concert in regulating IRES-dependent translation during infection. Altogether, we found that the stem-loop I of SVA is an essential element for IRES-dependent translation activity and viral replication.

Achieving a balance between enhancing both humoral and cellular immunity while ensuring sustained release for attenuated live vaccines has long been a challenge in the vaccine industry. However, the incorporation of chemical materials as nanoadjuvants has emerged as a promising strategy to address this challenge. In this study, a novel nano-adjuvant with sustained release properties was developed by combining polyethylene glycol (PEG) and other biochemical and molecular biology agents with CpG. The efficacy of this adjuvant was assessed using the widely applied CSF attenuated live vaccine. The body temperature and relative daily weight gain results demonstrated the safety of the formulations. Importantly, the combination of CpG immune enhancers and sustained-release agents led to a synergistic augmentation of both humoral and cellular immune responses. Specifically, the combination of PEG20000 and benzoic acid, along with Seppic white oil, significantly enhanced humoral immunity. In contrast, the combination of total white oil, PEG6000 and benzoic acid demonstrated superior efficacy in promoting cellular immunity. This study offers important insights into enhancing vaccine efficacy through novel adjuvant combinations, which can be applied to the development of more effective vaccines in the future.

Picornaviruses pose a significant threat to both human and animal health, causing many diseases in humans and swine. Porcine sapelovirus (PSV) is a globally reported enteric picornavirus commonly associated with subclinical or mild enteric infections in swine populations. Critically, unlike other neurotropic picornaviruses such as Enterovirus A71, no PSV strain has been reported to breach the blood–brain barrier (BBB). Since 2023, outbreaks of diarrhea with concurrent neurological signs like ataxia and lameness have been observed in weaned piglets across China, in particular, on a farm in Zhejiang province in 2025 with 100% morbidity and 20% mortality among the cases. Routine diagnostics ruled out common swine pathogens, but qPCR was positive for PSV. We successfully isolated three PSV strains (ZJ, FJ, SD) from affected piglets. Genetic analysis revealed that the PSV-ZJ is a novel recombinant between strains YC2011/2012 (China, 2011) and XTND/2019 (Vietnam, 2018). Pathogenicity assessment confirmed that the recombinant PSV-ZJ is highly pathogenic, causing severe diarrhea, growth retardation, and significant viral shedding via the respiratory and digestive tracts. qPCR and histopathology confirmed viral presence in intestinal and brain tissues, indicating that PSV-ZJ can cross the blood–brain barrier. This study presents the first quantitative viral load and histopathological data for a highly pathogenic recombinant PSV strain in China and emphasizes the critical role of recombination in driving viral virulence evolution, necessitating enhanced surveillance and the development of targeted preventive strategies.