Abstract
Tick-borne relapsing fever is an infectious disease caused by Borrelia species and are primarily transmitted by Ornithodoros ticks. Prior work indicated that in vitro cultivated 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 from B. turicatae grown 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 with B. turicatae grown 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. Quantifying B. turicatae in tick tissues indicated that by 300 generations they no longer colonized the vector. The results indicate that in vitro cultivation 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.
Highlights
Relapsing fever (RF) is a global and emerging vector-borne disease caused by spirochetes in the genus Borrelia
A polyclonal population of the 91E135 isolate of B. turicatae was used in this study [10], and spirochetes were cultured in modified Barbour-Stoenner-Kelly medium [14,15]
Genomic DNA from B. turicatae grown between 30 to 300 generations was isolated by phenol-chloroform extraction, and plasmid profiles were evaluated by pulse-field agarose gel electrophoresis, as previously described [11,16]
Summary
Relapsing fever (RF) is a global and emerging vector-borne disease caused by spirochetes in the genus Borrelia. The pathogens are transmitted by human body lice, ixodid, and argasid ticks [1,2], and the disease is burdensome on the impoverished. Clinical manifestation includes high fever, neurological symptoms, nausea, vomiting, preterm labor, and miscarriage [1]. There are several knowledge gaps regarding pathogenesis and the overall genomic stability of the spirochetes during laboratory cultivation. The impact of genomic instability on the tick-mammalian transmission cycle of vector borne spirochetes has been demonstrated in Lyme disease (LD) causing pathogens [3,4].
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