The impact ofin vitrocultivation on the natural life cycle of the tick-borne relapsing fever spirocheteBorrelia turicatae

Tick-borne relapsing fever is an infectious disease caused byBorreliaspecies and are primarily transmitted byOrnithodorosticks. Prior work indicated thatin vitrocultivated spirochetes remain infectious to mice by needle inoculation; however, the impact of laboratory propagation on the pathogens natural life cycle has not been determined. Our current study assessed the effect of serial cultivation on the natural tick-mammalian transmission cycle. First, we evaluated genomic DNA profiles fromB.turicataegrown to 30, 60, 120, and 300 generations, and these spirochetes were used to needle inoculate mice. Uninfected nymphal ticks were fed on these mice and acquisition, transstadial maintenance, and subsequent transmission after tick bite was determined. Infection frequencies in mice that were fed upon by ticks colonized withB.turicataegrown to 30, 60, and 120 generations were 100%, 100%, and 30%, respectively. Successful infection of mice by tick feeding was not detected after 120 generations. QuantifyingB.turicataein tick tissues indicated that by 300 generations they no longer colonized the vector. The results indicate thatin vitrocultivation significantly affects the establishment of tick colonization and murine infection. This work provides a foundation for the identification of essential genetic elements in the tick-mammalian infectious cycle.