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.
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 are due to B. hermsii and B. turicatae and occur in the western United States and Canada.
In pts with a compatible history (i.e., a characteristic fever pattern and exposure to body lice or soft-bodied ticks 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.
Treatment: Relapsing Fever
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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.
For a more detailed discussion, see Lukehart SA: Endemic Treponematoses, Chap. 207e; Hartskeerl RA, Wagenaar JFP: Leptospirosis, Chap. 208, p. 1140; Barbour AG: Relapsing Fever, Chap. 209, p. 1146; and Steere AC: Lyme Borreliosis, Chap. 210, p. 1149, in HPIM-19. For a discussion of syphilis, see Chap. 83. Sexually Transmitted and Reproductive Tract Infections in this manual. |
Section 7. Infectious Diseases