Characterization of a local case of severe fever with thrombocytopenia syndrome in Shenzhen, China: Clinical and immunological insights

• First local SFTS case in Shenzhen with DBV gene rearrangement. • Serum samples from patient and contacts tested for DBV via RT-PCR and ELISA. • SZ-202,101 strain genotype BCB, no recombination detected. • Comprehensive study on immunological and pathological features of SFTS. • Current DBV sequencing research has significant limitations. An exhaustive analysis of the immunological and pathogenic features of the first locally acquired case of severe fever with thrombocytopenia syndrome (SFTS) in Shenzhen was conducted. Serum samples were dynamically collected from one patient presenting with fever and thrombocytopenia, as well as from his close contacts. The presence of Dabie bandavirus (DBV) RNA was detected using fluorescence quantitative reverse transcription polymerase chain reaction (RT-PCR), while specific IgM and IgG antibodies were identified via enzyme-linked immunosorbent assay (ELISA). The viral L (large), M (medium), and S (small) segments were sequentially amplified by PCR and then sequenced using Sanger sequencing. We performed amino acid comparisons with published DBV strain sequences to identify mutation sites and assess their potential functional implications. Subsequently, molecular genotyping was conducted, and segment reassortment and recombination analyses were performed for each viral segment. A 52-year-old man presented with a history of fever, mild cough, dizziness, and fatigue. Serum samples from the patient tested positive for Dabie bandavirus (DBV) nucleic acid five days after disease onset, while blood samples taken 12 days after onset were positive for DBV-specific IgM and negative for both nucleic acid and DBV-specific IgG. The L, M, and S segments of the virus strain named SZ-202,101 showed the highest sequence homology with the DBV strain HB2012–197 from Hubei Province; the similarities were 99.50 %, 99.49 %, and 99.60 %, respectively. When compared to the reference DBV strain HB29, SZ-202,101 exhibited amino acid mutations at 16, 24, and 6 sites in the L, M, and S segments, respectively. The mutations in the L segment were predominantly located in the Linker, Core Lobe, vRBL, Fingers, Fingermode, Thumb Ring, and CBD domains. For the M segment, mutations were concentrated in the A, B, β, C, IM, I, III, TM, and Linker domains. The S segment mutations were primarily found in the N-lobe and C-terminal domains. Genetic evolution analysis revealed that the L and S segments of the SZ-202,101 strain and the HB2012–197 strain were classified under the B genotype, while the M segment was associated with the C genotype; consequently, the genotype of SZ-202,101 was designated as BCB. The virus did not exhibit any signs of recombination. Regarding epidemiological investigation, given that the patient and his associate had no record of international travel or contact with known cases, this instance was classified as an autochthonous case. This marks the first local case of SFTS in Shenzhen since 2017 and the first identification of DBV genotype reassortment in the region. The Local case of SFTS in Shenzhen was attributed to a genetically reassorted DBVidentified as the BCB reassortment genotype. The potential influence of amino acid mutation sites within the L and M segments of SZ-202,101, the virus strain corresponding to this genotype, on virulence and transmissibility warrants further investigation.