A neutralization assay with a severe fever with thrombocytopenia syndrome virus strain that makes plaques in inoculated cells

- Repeating passage of severe fever with thrombocytopenia syndrome virus (SFTSV) in cell culture changes the viral phenotype, by which SFTSV shows cytopathic effects in inoculated cells.
- The changed phenotype is due to mutations in the viral glycoprotein gene.
- The passaged strain of SFTSV is usable in neutralization test.

Severe fever with thrombocytopenia syndrome (SFTS) is a recently-discovered, potentially fatal infectious disease caused by SFTS virus (SFTSV). Due to the inability of SFTSV to make clear cytopathic effects (CPE) in cell culture, titration and neutralization assays of the virus require immunostaining of inoculated cells; consequently, the assays are time-consuming and expensive. In this report, we demonstrate the use of a highly-passaged SFTSV strain, p50-2, in a neutralization assay, which made clear plaques in inoculated Vero cells under neutral red staining. Furthermore, we performed molecular analyses to determine the characteristics of the strain. The results suggested that a single amino acid mutation within the viral glycoprotein conferred the ability to make clear plaques to SFTSV.