Genetic characterization of severe fever with thrombocytopenia syndrome virus in ticks from livestock environments in South Korea

Abstract

Introduction Severe fever with thrombocytopenia syndrome (SFTS), caused by the SFTS virus (SFTSV), is a highly fatal tick-borne zoonosis that poses a substantial public health threat. Although livestock husbandry environments represent important ecological settings for viral maintenance and circulation, molecular surveillance within these settings remains insufficient. Methods We conducted an annual systematic entomological and molecular survey from March to October between 2023 and 2025 in South Korea, targeting 204 environments adjacent to cattle, horse, deer, goat, and sheep farms. Results Among 101,006 field-collected ticks, Haemaphysalis longicornis was the most abundant species (90.62%), followed by Haemaphysalis flava (8.20%) and Ixodes nipponensis (1.10%). Molecular screening of the SFTSV S-segment revealed 65 positive pools, corresponding to a minimum infection rate (MIR) of 0.06%, with the highest MIR observed in cattle-associated tick populations (0.09%). Phylogenetic analysis demonstrated that all identified strains in this study clustered within the Japanese/Korean clade of genotype B2. Six out of seven contemporary strains shared 100.00% nucleotide identity and were identical to historical domestic human isolates from 2014, demonstrating high longitudinal sequence conservation within the analyzed partial S-segment region. Concurrently, detection of SFTSV strain 24CC401 in I. nipponensis larvae provided indirect field-based evidence consistent with potential transovarial persistence. This larval isolate displayed a distinct molecular profile with a 0.65% nucleotide divergence and two nonsynonymous mutations (G129E and V158E). Discussion Our findings indicate that specific genotype B2 lineages were detected in livestock-adjacent environments, suggesting a potential ecological association with livestock farming. Although the observed sequence conservation may support continued evaluation of conserved S-segment regions for molecular surveillance, the functional significance of the mutations identified in the larval isolate remains to be determined. Continued molecular surveillance may help characterize SFTSV genetic variation in ticks from livestock-associated environments.