Molecular characterization of tick-virus interactions.

All viruses infecting ticks (with one possible exception) are arboviruses; their life cycle depends on infection and replication in both tick and vertebrate host cells. Little is known of arbovirus-tick cell interactions even though tick-borne viruses spend most of their existence in ticks. A distinct selection pressure on tick-borne viruses is the intracellular process of bloodmeal digestion in ticks (contrasting with insects) This may explain the pronounced differences in surface structure of tick-borne and insect-borne orbiviruses. Some indications of molecular interactions can be extrapolated from vertebrate cells, such as utilisation of aggresome pathways. Although many (if not all) tick-borne viruses exploit the immunomodulatory effects of tick saliva on the vertebrate host, there is no evidence they interact directly with saliva molecules. However, the most fundamental question to address is the benign infection of arboviruses in tick cells compared with their cytopathic effect in vertebrate cells. As the tick proteome is unravelled, its interaction with the viral proteome should help explain the interactions between ticks and the many important viruses they transmit.