Pathogen isolation and traceability analysis of a fatal case of severe fever with thrombocytopenia syndrome virus (SFTSV) infectious encephalitis in China.

Background: The initial clinical symptoms of severe fever with thrombocytopenia syndrome (SFTS) mainly include high fever, thrombocytopenia and gastrointestinal symptoms, and severe patients may suffer from severe complications such as multiple organ failure, which can lead to death. Studies have shown that central nervous system symptoms are associated with severe adverse outcomes of SFTS, but there are few reports on confirmed cases of SFTS encephalitis. This is a special case in which her initial SFTS symptoms were atypical, while the disease deteriorated rapidly after the appearance of encephalitis. The purpose of this study was to report the clinical and epidemiological features of this case, isolate and trace the SFTS virus (SFTSV) strain, identify the genotype of the strain, and speculate on the infection route to provide an important reference for the diagnosis and control of SFTSV.

Methods: Cerebrospinal fluid and serum samples were collected, multipathogen detection was performed via next-generation sequencing (NGS), and SFTSV virus isolation was performed via inoculation of the samples with Vero cells. The serum of key populations closed to patients, parasitic ticks on the surface of domestic animal bodies and environmentally free ticks were collected for SFTSV monitoring. The whole genomes of the virus strains and positive nucleic acid samples were sequenced and compared with the GenBank reference sequence to construct a phylogenetic analysis tree.

Results: This patient was diagnosed with SFTSV encephalitis, and the viral strain was successfully isolated. The SFTSV strain is closely related to the Hubei strain HB2017-02, and the SFTSV M and L fragments belong to the B genotype, whereas the M fragments belong to the F genotype. In addition, the similarities of coding sequences of case strain to those of tick-carried SFTSV strain in the residence were more than 99.9%.

Conclusions: The patient was confirmed to have SFTSV-infected encephalitis and died rapidly. The SFTSV strain was of Chinese local origin, and tick bites were the most likely route of infection.