Objective To analyze continuous surveillance results of forest encephalitis virus in ticks in Arxan port area, Inner Mongolia autonomous region from 2023 to 2026, evaluate the virus carriage level and transmission risk of vector ticks, and provide evidence for the local prevention and control of tick-borne infectious diseases.

Methods From late April to early May in each year during 2023−2026, free-living ticks were collected by flagging method in the forest-steppe-wetland-farmland ecotone in Arxan port area. Tick species were identified by morphological observation combined with mitochondrial cytochrome c oxidase subunit Ⅰ (COⅠ) gene sequencing. Tick samples with a total weight of 1 g were randomly selected for metatranscriptomic sequencing to screen tick-borne viruses. In 2026, on the premise of meeting the sample size requirement for metatranscriptomic sequencing, an additional 460 Ixodes persulcatus ticks were collected and pooled at 5 ticks per tube. Nucleic acids were extracted and reverse-transcribed, followed by reverse-transcription polymerase chain reaction (RT-PCR) detection. Descriptive epidemiological methods were used to calculate pool-positive rate and minimum infection rate. Phylogenetic analysis was performed on near-full-length TBEV genomic sequences obtained from metatranscriptomic data.

Results Metatranscriptomic sequencing continuously detected forest encephalitis virus sequences in Ixodes persulcatus samples from Arxan port area during 2023−2026, with assembled lengths of 11074 bp, 11030 bp, 11300 bp and 11373 bp, respectively. The relative abundance of forest encephalitis virus (reads per million, RPM) increased steadily from 1273.43 in 2023 to 83 119.40 in 2026, and its abundance rank in tick-associated viral communities rose from the 7^th to the 1^st. The RT-PCR detection of pooled Ixodes persulcatus samples in 2026 showed that 22 pools were forest encephalitis virus nucleic acid positive; the pool-positive rate was 23.91% (22/92), and the minimum infection rate was 4.78% (22/460). The phylogenetic analysis revealed that the forest encephalitis virus sequences from Arxan port were closely related to epidemic strains circulating in Mongolia and Siberia of Russia, all belonging to Siberian subtype, with nucleotide identities of 97.35% and 97.15%, respectively.

Conclusion Forest encephalitis virus was persistently detected in Ixodes persulcatus in Arxan port area from 2023 to 2026, indicating the natural spread of forest encephalitis virusin this area. The RPM value and RT-PCR positive level of forest encephalitis virus in 2026 were higher than those in previous surveys, suggesting potential elevated transmission risk of forest encephalitis virus, which requires further continuous monitoring. It is suggested to strengthen etiological surveillance in Ixodes persulcatus and host animals, improve the molecular traceability system, and conduct targeted health education and risk warning.