Detection of Tickborne Relapsing Fever Spirochete, Austin, Texas, USA

Jack D. Bissett; Suzanne Ledet; Aparna Krishnavajhala; Brittany A. Armstrong; Anna Klioueva; Christopher Sexton; Adam Replogle; Martin E. Schriefer; Job E. Lopez

Disclosures

Emerging Infectious Diseases. 2018;24(11):2003-2009. 

In This Article

Discussion

We report TBRF in a patient from Austin, Texas. The patient had limited travel history outside Austin in the days before onset of signs and symptoms. Real-time PCR amplification of the B. turicatae glpQ gene and seroconversion for B. turicatae rBipA also helped identify the causative agent. Given that the suspected exposure site was previously investigated by Austin Public Health but ticks were not found, it was useful to collect O. turicata ticks near the site and assess their infectious status. Tick transmission feedings resulted in propagation of 3 isolates (BRP1, BRP1a, and BRP2), and results of multilocus sequencing of these isolates were identical to those of a human isolate and a tick isolate.[3,9,11] Assessment of total genomic DNA indicated plasmid diversity between the 3 strains and the 91E135 isolate. Ticks that transmitted BRP1 and BRP1a were collected from the same den area at separate times during the year, which suggests circulation of >2 B. turicatae variants in the tick population.

Little effort has been invested in active surveillance of TBRF in Texas over the past 70 years,[22,23] and more work is needed to understand the burden of this disease and maintenance of the spirochete in nature. Evidence indicates the endemicity of O. turicata ticks in San Antonio, Dallas, and Austin,[7,22,24] the seventh, ninth, and eleventh most populous cities, respectively, in the United States. O. turicata ticks are considered an arthropod reservoir of B. turicatae because they have a 10-year life span and might endure years of starvation while retaining the ability to transmit B. turicatae.[25]O. turicata ticks have also been collected in a variety of habitats, including caves, dens, rodent nests, and human dwellings.[2,7,9] However, there is a paucity of information regarding mammals involved in maintaining B. turicatae in nature.

The life cycle of B. turicatae in the vertebrate host consists of periods when the bacterium is undetectable in the blood.[5,13] Thus, indirect approaches are needed for improved surveillance. rBipA can support these studies because of the specificity of the protein to TBRF spirochetes.[12,13] BipA homologs have not been identified in other pathogens, and previous studies indicated that serologic responses to the protein can discriminate between infections caused by Lyme disease and TBRF Borrelia species.[12,13] Future efforts will focus on using rBipA as a novel diagnostic antigen for surveillance of B. turicatae.

TBRF is typically considered a disease of outdoor enthusiasts and impoverished persons living in primitive conditions.[1–3,11,15,26] However, our study suggests emergence of B. turicatae in urban areas. The location where ticks were collected was in a densely populated region of the city. However, the maintenance of this pathogen in nature remains unclear. The elusive life cycle of O. turicata ticks also poses challenges in understanding the ecology of B. turicatae. Furthermore, given the nonspecific clinical manifestations of disease, the public health effect of B. turicatae remains vague. Our findings indicate that surveillance efforts should be increased in Austin, Texas, to evaluate emergence of TBRF.

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