Evaluation of Oz virus susceptibility in several vertebrate cell lines and its application in efficient isolation from field-collected ticks

This study evaluates the susceptibility of multiple vertebrate cell lines to Oz virus (OZV) and demonstrates an improved approach for isolating the virus from field-collected ticks. OZV, a tick-borne thogotovirus associated with the first fatal human case in Japan, was assessed for replication efficiency in eight vertebrate-derived cell lines. Among these, BHK-21, Vero, HuH-7, and Huh7.5.1–8 cells supported high viral titers (>107 PFU/mL), with BHK-21 identified as the most suitable medium for virus isolation. Using this optimized system, the authors successfully isolated a new OZV strain, designated 23AT5, from Amblyomma testudinarium ticks collected in the same area where the original strain EH8 was identified. Genomic and phylogenetic analyses revealed that the new isolate is highly conserved and closely related (99.75-100% similarity at nucleotide level) to the original strain EH8, indicating long-term stability of the local transmission cycle. Two to three nucleotide polymorphisms have been identified in all segments and formed a robust clade with strain EH8 during phylogenetic analyses. Overall, the study provides important methodological and epidemiological insights into OZV maintenance and surveillance.
(TMR)