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

Abstract and Introduction

Abstract

In March 2017, a patient became febrile within 4 days after visiting a rustic conference center in Austin, Texas, USA, where Austin Public Health suspected an outbreak of tickborne relapsing fever a month earlier. Evaluation of a patient blood smear and molecular diagnostic assays identified Borrelia turicatae as the causative agent. We could not gain access to the property to collect ticks. Thus, we focused efforts at a nearby public park, <1 mile from the suspected exposure site. We trapped Ornithodoros turicata ticks from 2 locations in the park, and laboratory evaluation resulted in cultivation of 3 B. turicatae isolates. Multilocus sequencing of 3 chromosomal loci (flaB, rrs, and gyrB) indicated that the isolates were identical to those of B. turicatae 91E135 (a tick isolate) and BTE5EL (a human isolate). We identified the endemicity of O. turicata ticks and likely emergence of B. turicatae in this city.

Introduction

Globally, spirochetes that cause tickborne relapsing fever (TBRF) are neglected pathogens, and diagnosis of this disease is challenging because of its nonspecific manifestations. Signs and symptoms of TBRF include cyclic febrile episodes, nausea, and vomiting.[1] The bacterium Borrelia turicatae is the primary known causative species of TBRF in low-elevation, arid regions in the southern United States, and a unique manifestation of this disease is neurologic symptoms that further complicate an accurate diagnosis.[2] In Texas, most cases of infection with B. turicatae have been associated with cave explorers, outdoor enthusiasts, undocumented migrants, and military personnel.[2,3] Currently, it is not mandatory to report a diagnosis of TBRF in Texas.

An additional complication with defining public health effects of infection with B. turicatae is the dynamics between the pathogen and its tick vector (Ornithodoros turicata). These ticks have a life span of 10 years and can endure starvation for >5 years. However, B. turicatae remains infectious in these ticks.[4] Except for persons bitten in karst formations (topographies formed from dissolution of soluble rocks) that can contain swarms of O. turicata ticks,[2] attached ticks are rarely seen because these ticks are rapid feeders and transmission of B. turicatae occurs within seconds of the tick bite.[5,6] In addition, B. turicatae is maintained transovarially and tick larvae are difficult to see because of their small size.[6] After feeding, ticks return to their cavity dwelling, which includes wood cracks, leaf litter, and small- and medium-size mammal nests and dens.[2,7,8]

Little is known regarding the maintenance of B. turicatae in nature. Most laboratory isolates have resulted from feeding field-collected ticks on immunologically naive mice and culturing the spirochetes from infected murine blood.[9]B. turicatae has also been cultured from the blood of sick domestic dogs[9,10] and a human.[11] Furthermore, there is an absence of B. turicatae isolates from wild vertebrates, which further limits understanding the etiology of TBRF.

We report clinical manifestations of TBRF for a patient from Austin, Texas, USA. Using species-specific genetic and antigenic markers,[12–14] we identified the etiologic agent as B. turicatae. Because access to the alleged exposure site was not available, we collected O. turicata ticks in a nearby public park. Collected ticks indicated the endemicity of the vector to Austin. These ticks were evaluated for infection by feeding them on immunologically naive mice. We report the transmission and isolation of TBRF spirochetes in culture medium. Partial sequencing of the flagellin B (flaB), 16S rRNA (rrs), and DNA gyrase B (gyrB) genes (total 2,398 bp) indicated probable emergence of B. turicatae in Austin, Texas.

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