Tick-borne relapsing fever is a disease caused by one of several spirochetes from the Borrelia genus. This infection is not encountered in Australia, but it is otherwise encountered worldwide and should be considered in a patient with recent travel. In the United States, the most common organism responsible for this infection is Borrelia hermsii, transmitted by the soft-body tick Ornithodoros hermsii primarily found at higher elevations in the western United States.
The infectious organism is transmitted to humans while the tick is taking a blood meal at night. All stages of the tick can transmit the infection, and the blood meal (and transmission of the infectious organism) is usually complete in 20 minutes. The bite of the tick is painless, and the patient may not recall a bite. A travel and exposure history should be obtained to determine if the patient has recently been camping or has had any known or possible exposure to rodents or other animals known to be reservoirs of the infection including rabbits.
The first febrile episode usually begins after an incubation period of about 1-2 weeks. The fever can be quite high (up to 105° F) and usually culminates with a "crisis" with rigors, rising temperature, tachycardia, and hypertension followed by profuse diaphoresis and hypotension. Following the first fever, associated symptoms may include headache, muscle and joint aches, and nausea, with recurrence of fever at least twice. A nonspecific rash may also be present. Central nervous system involvement is estimated to occur in 9% of cases and may manifest as lymphocytic meningitis or altered mental status. Uncommon manifestations of the infection include iritis, acute respiratory distress syndrome, and myocarditis.
The first febrile episode lasts about 3 days and corresponds to periods when spirochetes are most likely to be seen in the blood. Laboratory evaluation may reveal leukocytosis, thrombocytopenia, and elevated liver transaminases. The patient is then typically afebrile for about 1 week before a recurrence of symptoms occurs. Antigenic shift of outer surface proteins of the organism is responsible for the relapsing symptoms.
As opposed to patients infected with louse-borne relapsing fever who typically have only 1 or 2 episodes of relapsing symptoms, patients with tick-borne relapsing fever can have many relapses.
Mortality occurs in approximately 2%-5% of cases, which is a lower rate than for louse-borne relapsing fever. Death due to the infection is rare in the United States. Infection during pregnancy has been associated with spontaneous abortion.
Treatment is with antibiotics. Jarisch-Herxheimer reaction may occur after antibiotic therapy is started.
Tick-borne relapsing fever
Alerts and Notices
Synopsis
Codes
ICD10CM:
A68.1 – Tick-borne relapsing fever
SNOMEDCT:
10301003 – Tick-borne relapsing fever
A68.1 – Tick-borne relapsing fever
SNOMEDCT:
10301003 – Tick-borne relapsing fever
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Differential Diagnosis & Pitfalls
- Malaria – This infection should always be considered in a febrile patient with a compatible travel history. Thick and thin blood smears and malaria antigen testing should be performed.
- Babesiosis – Consider this in patients with compatible travel history (to the U.S. Northeast and upper Midwest). Diagnosis is made by microscopy or polymerase chain reaction (PCR).
- Colorado tick fever – Most patients recall a tick bite. As with tick-borne relapsing fever, the fever in this disease can recur. Diagnosis can be made by serology or PCR.
- Human ehrlichiosis and anaplasmosis – Tick-borne illness presenting with fever, malaise, myalgia, headache, and chills. Diagnosis is made by serology and PCR.
- Brucellosis – Fever in acute infection can sometimes last weeks. Diagnosis can be made by culture, serology, or PCR.
- Bartonella infection – In trench fever, recurrent febrile episodes can occur. Diagnosis can be made by culture, serology, or PCR.
- Tularemia – Following the initial febrile episode, the patient may experience an afebrile period lasting a few days before the fever returns. Diagnosis can be made by serology or PCR.
- Leptospirosis – This is a febrile illness caused by a pathogenic spirochete found in animal urine and contaminated water and soil. Diagnosis can be made by culture, serology, or PCR.
- Rat-bite fever – This is a febrile illness caused by Streptobacillus moniliformis or Spirillum minus. Patients typically have a rash on their extremities and polyarthritis.
- Yellow fever – This illness should be considered if there has been travel to an area of South America or Africa where transmission is known to occur. Diagnosis can be made with serology or PCR.
- Dengue fever – A minority of patients may have a relapse of fever that occurs a few days after the initial febrile episode. Diagnosis can be made by serology or PCR.
- Lymphocytic choriomeningitis virus infection – A rodent-borne viral infection that presents as aseptic meningitis. Diagnosis is by serology on acute and convalescent serum.
- Systemic juvenile idiopathic arthritis or adult-onset Still disease – Fever is a very common extra-articular manifestation of these conditions. Patients will typically lack a travel and exposure history that would be compatible with tick-borne relapsing fever. The fever will not respond to antibiotics.
- Occult malignancy – Certain malignancies including lymphoma, leukemia, and renal cell carcinoma may present with fever.
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Last Updated:07/21/2020