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Relapsing fever is an infection transmitted by a louse or tick. It is characterized by repeated episodes of fever.

Alternative Names

Tick-borne relapsing fever, Louse-borne relapsing fever

Causes, incidence, and risk factors

Relapsing fever is an infection caused by several species of bacteria in the Borrelia family.

There are two major forms of relapsing fever:

  • Tick-borne relapsing fever (TBRF) is transmitted by the Ornithodoros tick and occurs in Africa, Spain, Saudi Arabia, Asia, and certain areas in the western United States and Canada. The bacteria species associated with TBRF are Borrelia duttoni, Borrelia hermsii, and Borrelia parkerii.
  • Louse-borne relapsing fever (LBRF) is transmitted by body lice and is most common in Asia, Africa, and Central and South America. The bacteria species associated with LBRF is Borrelia recurrentis.

Sudden fever occurs within 2 weeks of infection. In LBRF, the fever usually lasts 3-6 days and is usually followed by a single, milder episode. In TRBF, multiple episodes of fever occur and each may last up to 3 days. Individuals may be free of fever for up to 2 weeks before it returns.

In both forms, the fever episode may end in “crisis.” This consists of shaking chills, followed by intense sweating, falling body temperature, and low blood pressure. This stage may result in death in up to 10% of people.

After several cycles of fever, some people can develop dramatic central nervous system signs such as seizures, stupor, and coma. The Borrelia organism can also invade heart and liver tissues, causing inflammation of the heart muscle (myocarditis) and liver (hepatitis). Bleeding throughout the body and pneumonia are other complications.

In the United States, TBRF often occurs west of the Mississippi River, particularly in the mountainous West and the high deserts and plains of the Southwest. In the mountains of California, Utah, Arizona, New Mexico, Colorado, Oregon, and Washington, infections are usually caused by Borrelia hermsii and are often acquired in cabins in forests. It is possible that the risk now extends into the southeastern United States.

LBRF is mainly a disease of the developing world. It is currently seen in Ethiopia and Sudan. Famine, war, and the movement and groups of refugees often result in epidemics of LBRF.


  • Bleeding
  • Coma
  • Headache
  • Joint aches (arthralgia), muscle aches (myalgia)
  • Nausea and vomiting
  • Sagging of one side of the face (facial droop)
  • Stiff neck
  • Sudden onset of high fever, shaking chills, seizure 
  • Vomiting
  • Weakness, unsteady while walking

Signs and tests

Relapsing fever should be suspected if someone coming from a high-risk area has repeated episodes of fever. This is particularly true if the fever is followed by a “crisis” stage, and if the person may have been exposed to lice or soft-bodied ticks.

Tests that may be done include:

  • Blood smear to determine the cause of the infection
  • Blood antibody tests, sometimes used but their usefulness is limited


Treatment involves antibiotics, most often tetracycline, doxycycline, erythromycin, or penicillin.

Expectations (prognosis)

Death rate for untreated LBRF ranges from 10 – 70%. With TBRF, it is 4 -10%. With early treatment, the death rate is reduced. Persons who have developed coma, myocarditis, liver problems, or pneumonia are more likely to die.


  • Coma
  • Facial droop
  • Liver dysfunction
  • Meningitis
  • Myocarditis — may lead to arrhythmias
  • Pneumonia
  • Seizures
  • Shock related to taking antibiotics (Jarisch – Herxheimer’s reaction, in which the rapid death of very large numbers of Borrelia organisms induces shock)
  • Weakness
  • Widespread bleeding

Calling your health care provider

Contact your medical provider right away if you are a returning traveler and develop a fever. Different possible infections need to be investigated in a timely manner.


For TBRF, wearing clothing that fully cover the arms and legs when outdoors can help prevent infection. So can using insect repellent such as DEET on the skin and clothing. Tick and lice control in high-risk areas is another important public health measure.