Wei X, et al.
Identification and phylodynamic analysis of the Siberian subtype of tick-borne encephalitis virus in tick-bitten patients from northeastern China. Transbound Emerg Dis. 2025;Article ID 3756652. doi:10.1155/tbed/3756652
Previously, the Far Eastern (FE) subtype of tick-borne encephalitis virus (TBEV) was considered the only subtype endemic in China (see Snapshot week 41/2024). However, in 2024, the Siberian (Sib) subtype was detected in ticks in the Daxing’an Mountains of northeastern China (see Snapshot week 39/2024), suggesting co-circulation of FE and Sib subtypes in this region.
In the present study, the authors analyzed the epidemiological, clinical, and phylogenetic characteristics of newly identified Sib TBEV strains from human patients.
Seven tick-bitten patients (aged 26–53 years) from northeastern China developed TBE following incubation periods of 7–28 days. None had received TBE vaccination. Hospital stays ranged from 5 to 21 days.
Complete viral genome sequences were successfully obtained from all seven patients. Phylogenetic analysis assigned these strains to the Siberian subtype, specifically the Zausaev and Vasilchenko lineages. The sequences showed high identity with corresponding Russian strains from these lineages. In addition, three serum samples from other tick-bitten individuals in the same region tested positive for the FE subtype.
Bayesian phylodynamic analysis indicated that the identified Sib strains did not emerge recently but likely date back to the late 19th century. This suggests that the Siberian subtype may have been circulating in China for decades but remained undetected.
The identification of Sib strains alongside FE strains highlights increasing epidemiological complexity and poses new challenges for TBE surveillance, prevention, and control in China. Enhanced monitoring of TBEV in ticks, animal reservoirs, and exposed human populations is warranted.