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Key Features

Essentials of Diagnosis

  • Episodes of relapses fever, chills, malaise

  • Occasional rash, arthritis, cough, hepatosplenomegaly, conjunctivitis

  • Diagnosis suggested by direct microscopic identification of spirochetes in smears of peripheral blood

  • Diagnosis confirmed with serologic testing

General Considerations

  • There are two forms: epidemic relapsing fever is transmitted to humans by body lice (Pediculus humanus) and endemic relapsing fever by soft-bodied ticks (genus Ornithodoros)

  • Tick-borne relapsing fever is endemic in the western United States

  • Transmission usually takes place during the warm months, when ticks are active and recreation or work brings people into contact with ticks

  • Ticks are nocturnal feeders and remain attached for only 5–20 minutes; consequently, the patient seldom remembers a tick bite

  • Rarely, neonatal relapsing fever results from transplacental transmission of Borrelia

  • Both louse-borne and tick-borne relapsing fever may be acquired during foreign travel

Clinical Findings

Symptoms and Signs

  • Incubation period is 2–18 days

  • Attack is sudden, with high fever, chills, sweats, tachycardia, nausea and vomiting, headache, myalgia, and arthralgia

  • After 3–7 days, the fever falls

  • Relapses occur at intervals of several days to weeks and duplicate the initial attack but become progressively less severe

  • In louse-borne relapsing fever, there is usually a single relapse

  • In tick-borne infection, 2–10 relapses occur

  • Hepatomegaly, splenomegaly, pneumonitis, meningitis, and myocarditis may appear later in the course of the disease

  • An erythematous rash may be seen over the trunk and extremities, and petechiae may be present

  • Jaundice, iritis, conjunctivitis, cranial nerve palsies, and hemorrhage occur more commonly during relapses


  • During febrile episodes, the patient's urine contains protein, casts, and occasionally erythrocytes

  • Marked polymorphonuclear leukocytosis is present

  • Spirochetes can be found in the peripheral blood by direct microscopy in approximately 70% of cases by darkfield examination or by Wright, Giemsa, or acridine orange staining of thick and thin smears

  • Spirochetes are not found during afebrile periods

  • Immunofluorescent antibody (or ELISA confirmed by Western blot) can help establish the diagnosis serologically

Differential Diagnosis

  • Malaria

  • Leptospirosis

  • Dengue

  • Typhus

  • Rat-bite fever

  • Colorado tick fever

  • Rocky Mountain spotted fever

  • Collagen-vascular disease

  • Any fever of unknown origin


  • For children younger than age 8 years penicillin or erythromycin should be given for 10 days

  • Older children may be given doxycycline



  • Facial paralysis

  • Iridocyclitis, optic atrophy

  • Hypochromic anemia

  • Pneumonia

  • Nephritis

  • Myocarditis, endocarditis

  • Seizures


  • Measures that decrease exposures to soft ticks and body lice will prevent most cases

  • Soft-bodied ticks often are found in rodent burrows or nests, so decreasing rodent access to homes and eliminating rodents in the home is helpful

  • Body-louse infestation can ...

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