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Information ⬇

Microbiology

Borrelia recurrentis causes louse-borne relapsing fever (LBRF) and is transmitted from person to person by the body louse. Spirochetes are introduced not from the bite itself but from rubbing of the insect's feces into the bite site in response to irritation. Tick-borne relapsing fever (TBRF), a zoonosis usually transmitted via the bite of various Ornithodoros ticks, is caused by multiple Borrelia species. B. miyamotoi can cause relapsing fever but is transmitted to humans from other mammals by hard ticks (e.g., Ixodes scapularis) that also transmit B. burgdorferi and other tick-borne illnesses.

Epidemiology

LBRF transmission is currently limited to Ethiopia and adjacent countries, with epidemics occurring during famine, natural disaster, and war. TBRF occurs worldwide, with Africa most affected. In North America, most cases of TBRF are due to B. hermsii and B. turicatae and occur in the western United States and Canada.

Clinical Manifestations

  • Both TBRF and LBRF present with a sudden onset of discrete febrile periods separated by afebrile periods of a few days.
    • In LBRF, the first episode of fever persists for 3-6 days and is followed by a single milder episode.
    • In TBRF, multiple febrile periods last 1-3 days each.
    • In both forms, the duration of an afebrile period ranges from 4 to 14 days.
  • In addition to fever, pts commonly develop headaches, myalgias, nausea, abdominal pain (due to hepatosplenomegaly), and arthralgias.
    • Petechiae, ecchymoses, and epistaxis are common in LBRF but not in TBRF.
    • Localizing neurologic findings (e.g., Bell's palsy, deafness, visual impairment) are more common in TBRF.

Diagnosis

In pts with a compatible history (i.e., a characteristic fever pattern and exposure to body lice, soft-bodied ticks, or Ixodes hard-bodied ticks in at-risk geographic regions 1-2 weeks prior to illness onset), laboratory confirmation is made by the detection or isolation of spirochetes from blood during a febrile episode. Microscopic examination of Wright- or Giemsa-stained thin blood smears usually yields positive results if the concentration of spirochetes is ≥105 /mL.

  • PCR techniques may reveal spirochetes between febrile episodes.
  • Serologic confirmation of infection is limited by false-positive results and poor sensitivity.
TREATMENT

Relapsing Fever

  • One dose of doxycycline (200 mg PO), tetracycline (500 mg PO), or penicillin G (400,000-800,000 units IM) is effective for LBRF. A 10-day course of tetracycline (500 mg q6h) or doxycycline (100 mg bid) is preferred for TBRF; erythromycin (500 mg q6h) is an alternative when tetracyclines are contraindicated. The Jarisch-Herxheimer reaction, which has an incidence of ∼80% in LBRF and ∼50% in TBRF, presents as rigors, fevers, and hypotension within 2-3 h of initiation of antibiotic therapy. Given that some cases are fatal, pts should be monitored for several hours following the first dose of antibiotics.
  • Little is known about treatment for B. miyamotoi infections, but the guidelines for Lyme disease are probably sufficient.

Prognosis

The mortality rates for untreated LBRF and TBRF are 10-70% and 4-10%, respectively. With treatment, the mortality rate is 2-5% for LBRF and <2% for TBRF.

Outline ⬆

Section 7. Infectious Diseases