Tracking of Transmission from Infected Nymphs to Mice.

Quantitative and microscopic tracking of transmission from infected nymphs has shown a transmission cycle different from that of and organisms are abundant in the guts of unfed nymphs, and their numbers continuously decrease during feeding. spirochetes are present in murine skin within 1 day of tick attachment. In contrast, spirochetes were not detectable in salivary glands at any stage of tick feeding. Further experiments demonstrated that tick saliva is not essential for infectivity, the most important requirement for successful host colonization being a change in expression of outer surface proteins that occurs in the tick gut during feeding. Spirochetes in vertebrate mode are then able to survive within the host even in the absence of tick saliva. Taken together, our data suggest that the tick gut is the decisive organ that determines the competence of to vector We discuss possible transmission mechanisms of spirochetes that should be further tested in order to design effective preventive and therapeutic strategies against Lyme disease.