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Tick-borne Relapsing Fever (TBRF) Overview

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Tick-borne relapsing fever (TBRF) is an infection caused by some species of spirochete bacteria in the genus Borrelia, including B. hermsii, B. parkeri, and B. turicatae. Borrelia spirochetes that cause TBRF are transmitted to humans through the bite of infected “soft ticks” of the genus Ornithodoros. Soft ticks feed briefly—usually for less than half an hour—and painlessly, so bites often go unnoticed. Each Borrelia species that causes TBRF is usually associated with a specific soft tick species: B. hermsii is transmitted by O. hermsi, B. parkeri by O. parkeri, and B. turicatae by O. turicata ticks.

The incubation period between a bite from an infected tick and onset of illness is typically one week. TBRF is characterized by periods of fever lasting 2-7 days, often exceeding 103oF, alternating with afebrile periods of 4-14 days. Febrile periods are often accompanied by shaking chills, sweats, headache, muscle and joint pain, and nausea/vomiting. TBRF is self-limiting in most instances but may be fatal in 5-10% of untreated cases. With appropriate treatment, most patients recover within a few days; however, TBRF can be very serious if contracted during pregnancy and can lead to spontaneous abortion, premature birth, or neonatal death.

TBRF is endemic in the western U.S. and is primarily associated with sleeping in rustic, rodent-infested cabins in mountainous areas. Most cases occur during the summer months when people are vacationing in these areas. The primary causative agent of TBRF in Texas is B. turicatae, transmitted by the soft tick O. turicata, which commonly inhabits caves and rodent burrows—consequently, many of the TBRF cases in Texas have been associated with cave exploration. Recognition and reporting of TBRF cases is critical to the identification and control of outbreaks. Tick-infested dwellings can remain a source of human infection for many years due to the long life span of the soft tick vectors.

Ornithodoros turicata tick

 

Relapsing Fever Tick

Ornithodoros turicata tick, from https://www.dshs.state.tx.us/lab/entResources.shtm

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Last updated April 6, 2021