Genetic insights into dabie bandavirus from a clinical case of severe fever with thrombocytopenia syndrome in Longyou County, China.

objectiveTo conduct an epidemiological investigation on a case of severe fever with thrombocytopenia syndrome (SFTS) reported in Longyou County, Zhejiang Province in April 2025, and to perform nucleic acid detection and genetic characterization of Dabie bandavirus (DBV) in the patient's serum sample, aiming to provide scientific evidence and technical support for local SFTS prevention and control.

methodsAn epidemiological investigation was conducted on the case. Serum samples from the confirmed case and close contacts, as well as related vector host specimens, were collected. DBV-specific nucleic acid was detected using real-time fluorescent quantitative PCR. The viral genome was amplified by RT-PCR and subjected to whole-genome sequencing. Professional computer software (SeqMan Ultra 17.2, Clustal X 2.1, BioEdit V7.2.6.1, and MEGA V7.0.26, etc.) was used for nucleotide and amino acid sequence alignment, phylogenetic tree construction, and calculation of genetic distances and homology percentages.

resultsThe case had a history of tick bite and no history of travel outside the area. Fluorescence quantitative PCR detection showed that only the case's serum sample was positive for DBV nucleic acid, while serum samples from close contacts and related vector host specimens were all negative for DBV nucleic acid. After amplification and sequencing, the three fragments L, M, and S were successfully obtained. Genetic evolution analysis showed that they belonged to genotypes L (C), M (C), and S (A), respectively. Compared with the closest reference strain HZ2023-16 in the phylogenetic tree, the nucleotide homologies of the L, M, NS, and NP genes were 99.74%, 99.53%, 99.66%, and 99.19%, respectively, and the amino acid homologies were 100%, 99.72%, 99.66%, and 99.59%, respectively. Compared with the type C reference strain AHL/China/2011 (L(C)/M(C)/S(D)), the nucleotide homologies of the L, M, NS, and NP genes were 96.87%, 96%, 93.76%, and 95.66%, respectively, and the amino acid homologies were 99.42%, 98.51%, 98.29%, and 99.18%, respectively. Compared with the type A reference strain JX23XSH (L(A)/M(A)/S(A)), the nucleotide homologies of the L, M, NS, and NP genes were 96.24%, 95.97%, 95.35%, and 97.02%, respectively, and the amino acid homologies were 99.52%, 98.14%, 99.32%, and 99.18%, respectively. The average genetic distances of the L, M, and S genes compared with the HZ2023-16 reference strain were 0.003, 0.005, and 0.005, respectively; compared with the type C reference strain AHL/China/2011 (L(C)/M(C)/S(D)), they were 0.031, 0.04, and 0.053, respectively; compared with the type A reference strain JX23XSH (L(A)/M(A)/S(A)), they were 0.038, 0.04, and 0.038, respectively. Amino acid variation analysis showed that compared with the reference strains, this strain had 0-12 amino acid substitutions in the L protein (e.g., V68I, A140V), 3-20 substitutions in the M protein (e.g., D151E, G863S), 1-5 substitutions in the NS protein, and 1-2 substitutions in the NP protein.

conclusionCombining the clinical manifestations, epidemiological history, and laboratory test results of the case, this outbreak can be determined as a local case of severe fever with thrombocytopenia syndrome. The strain is genetically closely related to human-derived reference strains and possesses specific genomic characteristics.