Comparative transcriptomic insights into ticks infected by alongshan and tick-borne encephalitis viruses.

Ticks are hematophagous ectoparasites and key vectors of a wide range of pathogens, including viruses, bacteria, and protozoa. Climate change and environmental shifts have contributed to the expansion of tick populations and the pathogens they harbor. Ticks rely solely on their innate immune system to combat infections, utilizing mechanisms such as RNA interference, phagocytosis, and antimicrobial peptide expression. However, pathogens have evolved strategies to evade or manipulate these defenses to facilitate their replication and transmission. This study compares the infection dynamics of two tick-borne viruses: Orthoflavivirus encephalitidis (TBEV) and Alongshan virus (ALSV). TBEV, a well-adapted arbovirus, requires both tick and vertebrate hosts for its life cycle and is a major cause of human meningitis and encephalitis across Europe and Asia. In contrast, ALSV appears to be primarily restricted to ticks, with its dependence on vertebrate hosts still unclear. Transcriptomic analyses of Ixodes ricinus ticks revealed distinct gene expression patterns in response to these viruses. TBEV infection primarily regulated genes related to immunity, defense, and digestion-reflecting its adaptation to dual-host environments and acquisition via blood feeding. ALSV infection, however, influenced signaling and infection-related pathways, suggesting a more specialized adaptation to ticks. These findings underscore the differences in immune modulation and metabolic responses between TBEV and ALSV, highlighting the need for further genomic and proteomic studies to enhance our understanding of virus-vector interactions. Such insights could inform strategies for controlling tick-borne diseases and tracking pathogen evolution.