Development and evaluation of a whole-virus ELISA for severe fever with thrombocytopenia syndrome virus: Comparison with a recombinant nucleocapsid protein ELISA.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne pathogen listed as a World Health Organization priority virus, posing a serious public health threat. However, reliable serological assays remain limited, particularly for early IgM detection. In this study, we developed a safe and efficient indirect enzyme-linked immunosorbent assay (wv-ELISA) using β-propiolactone (BPL)-inactivated whole SFTSV virions as antigen and compared its performance with a recombinant nucleoprotein-based ELISA (rNP-ELISA). High-purity, structurally intact virions were prepared by large-scale SFTSV culture followed by polyethylene glycol precipitation and sucrose density gradient ultracentrifugation, then inactivated with 0.03% BPL to ensure biosafety while preserving antigenicity. Using serum samples from confirmed SFTSV patients and healthy volunteers, the IgM sensitivity of wv-ELISA and rNP-ELISA was 100% and 91.9%, respectively, with 100% specificity in both, when compared with the rNP-capture ELISA. While both assays performed comparably for IgG detection, the whole-virus ELISA exhibited superior sensitivity for IgM detection. Moreover, antibody titers measured by wv-ELISA showed significant negative correlations with viral RNA copy numbers and positive correlations with neutralizing antibody titers. Notably, IgG titers determined by wv-ELISA correlated more strongly with neutralizing activity than those measured by rNP-ELISA, likely reflecting the presence of native viral glycoproteins in the whole-virus antigen. Overall, this study establishes a safe, BPL-inactivated whole-virus ELISA system that offers high sensitivity and specificity for both IgM and IgG detection, providing a valuable tool for SFTSV serodiagnosis and immune evaluation.