Identification of transiently produced IgG linear epitopes in Senecavirus A for differentiating infected from vaccinated animals.

Differentiating infected from vaccinated animals (DIVA) is critical for disease eradication and emerging infection surveillance. Senecavirus A (SVA), which causes vesicular disease and neonatal mortality in pigs, is clinically indistinguishable from foot-and-mouth disease virus (FMDV), posing significant economic risks to swine production. Therefore, a reliable DIVA diagnostic method is urgently needed for accurate SVA detection. In this study, we employed the IgG sero-dynamic curves to aid epitope discovery (IsDAED) approach, utilizing peptide microarrays to identify transiently produced IgG (TPI)-associated linear B-cell epitopes on SVA structural proteins. VP2-15 emerged as a dominant linear epitope shared across multiple infected samples, exhibiting a characteristic short-lived antibody response. In addition, sample-specific epitopes VP2-4, VP3-12, and VP1-24 were also identified. Vaccination trials revealed that VP2-15 has a diagnostic window between 7 and 42 days post-boost (dpb), with a DIVA window established beyond 60 dpb. Challenge experiments following inactivated vaccine immunization confirmed that VP2-15 reliably indicates new infections. Virus neutralization test (VNT) and in vitro blocking assays revealed that VP2-15 peptide could partially block the neutralization effect of neutralizing antibodies on SVA. Still, it could not induce neutralizing antibodies in pigs. A diagnostic kit based on a combination of peptide probes (VP2-15, VP2-4, VP3-12, and VP1-24) exhibited high sensitivity (97.9 %) and specificity (90.6 %) in clinical samples, with no cross-reactivity to FMDV. Collectively, the antigenic epitopes identified in this study enable DIVA via TPI detection, offering a valuable tool for SVA surveillance and advancing both control strategies and our understanding of host-virus interactions.