Summary: Ticks as vectors for B. burgdorferi s.l., the etiologic agent of lyme borreliosis:
Lyme borreliosis, the most common tick borne human disease in the northern hemisphere, is a multisystem disease predominantly involving skin, nervous system, joints, and heart. The etiologic agents, summarized in the Borrelia burgdorferi sensu lato complex, meanwhile comprise 18 different species at least five of whom are human pathogenic, i.e., B. burgdorferi s.s., B. afzelii, B. garinii, B. bavariensis and B. spielmanii.
In Europe all human pathogenic species are present, while in the USA only B. burgdorferi s.s., and in Asia only B. garinii, B. bavariensis and B. afzelii were found. Relevant vectors for humans are hard ticks belonging to the Ixodes ricinus / I. persulcatus complex, namely I. ricinus in Europe overlapping with I. persulcatus in Eastern Europe, I. persulcatus in Asia, and I. scapularis and I. pacificus in the USA.
The sequence of events that happen at the pathogen-vector interface is a complex process that is far from being fully understood. An important basic requirement is the long duration of the hard ticks feeding that lasts up to more than 10 days.
This long time frame not only allows the tick to ingest and concentrate a huge amount of blood, but also allows B. burgdorferi to adapt by fundamental changes, e.g. in its protein expression pattern, to the completely different environments, the arthropod vector and the warm blooded host.
Recent studies on the vector-pathogen interaction revealed that the presence of borreliae in the tick induce fundamental changes in the tick like up-regulation of immunosuppressive factors that might not only aid the borreliae but also be favourable for the tick.
The knowledge and understanding of these complex interactions is an important prerequisite for development of preventive strategies as well as for prediction of future developments especially regarding climate changing.