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

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.

Keywords: Austin; Borrelia turicatae; Ornithodors turicata; Texas; United States; bacteria; borreliosis; diagnosis; elapsing fever spirochete; relapsing fever; spirochetes; tick-borne infections; ticks; vector-borne infections; zoonoses.

Figure 1

Giemsa-stained peripheral blood smear of a 34-year-old woman with tickborne relapsing fever, Austin, Texas, USA, showing 2 spirochetes (arrows). Scale bar indicates 20 μm.

Figure 2

Serologic responses to Borrelia turicatae protein lysates and rBipA in 34-year-old woman with tickborne relapsing fever, detected by immunoblotting, Austin, Texas, USA. A) Serum sample from the case-patient; B) positive control serum sample from another case-patient; C) negative control sample. Lane 1, B. turicatae; lane 2, rBipA. Values on the left are in kilobases. Asterisks (*) indicate the size of native BipA. rBipA, recombinant Borrelia immunogenic protein A.

Figure 3

Location of collection sites for Ornithodors turicata ticks, Austin Texas, USA. Two rodent dens (insets) were located at the base of an oak tree. Carbon dioxide traps were placed at the openings until ticks emerged. Borrelia turicatae isolates BRP1 and BRP1a originated from ticks that were collected from the den shown at bottom left, and isolate BRP2 originated from the den shown at the bottom right.

Figure 4

Reversed-field gel electrophoresis of Borrelia turicatae isolates collected from Ornithodors turicata ticks, Austin, Texas, USA (BRP1, BRP1a, and BRP2) and an isolate from previously field-collected ticks (91E135) (9). Lane 1, 91E135; lane 2, BRP1; lane 3, BRP1a; lane 4, BRP2. White boxes indicate a plasmid in BRP1 that is absent from the other strains (top); plasmids unique to BRP1, BRP1a, and BRP2 (middle); and a plasmid in 91E135 strain that is absent in isolates from Austin (bottom).