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Relapsing Fever

(Tick Fever; Recurrent Fever; Famine Fever)


Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Reviewed/Revised Nov 2022 | Modified Mar 2023
Topic Resources

Relapsing fever is an infection caused by certain Borrelia species, which are spiral-shaped bacteria called spirochetes (see figure ).

  • People are infected when they are bitten by an infected tick or come in contact with an infected louse.

  • People have sudden chills followed by a high fever, severe headache, vomiting, muscle and joint pain, and sometimes a rash.

  • Symptoms disappear, then return (relapse) several times.

  • Identifying the bacteria in a sample of blood confirms the diagnosis.

  • Antibiotics are usually effective.

Relapsing fever is transmitted by soft-bodied ticks, hard-bodied ticks, and body lice.

Relapsing fever caused by ticks (tick-borne relapsing fever)

A soft-bodied tick becomes infected when it feeds on rodents (such as chipmunks and squirrels) that carry a species of Borrelia bacteria. The tick spreads the bacteria to a person when it bites.

Tick-borne relapsing fever caused by soft-bodied ticks occurs in the Americas, Africa, Asia, and Europe. In the United States, the disease occurs mainly in the Western states, particularly between May and September. People who sleep in a rodent-infested cabin in the mountains are more likely to be bitten by infected ticks. However, because the ticks feed at night and do not remain attached for very long, people often do not recall a tick bite. People who explore caves (spelunking) are also at risk of infection.

Did You Know...

Soft ticks differ from hard ticks (such as the dog tick and the deer tick) in the following ways:

  • Soft ticks remain attached for a short time, usually less than half an hour.

  • Soft ticks do not wait for their prey in tall grass or brush. Instead, they live in rodent burrows, feeding as needed on the rodent as it sleeps.

Hard-bodied ticks that transmit relapsing fever are the same ticks that transmit Lyme disease. Thus, relapsing fever caused by hard-bodied ticks occurs in the same places where Lyme disease occurs in the United States—the Northeast and upper Midwest. When these ticks transmit relapsing fever, they may also transmit Lyme disease, and people may have more than one infection at a time.

The ticks become infected when they feed on the blood of rodents (such as the white-footed mouse) that carry a species of Borrelia bacteria. The tick spreads the bacteria to a person when it bites.

People who live in wooded areas or who walk through tall grass or wooded areas are more likely to be bitten by infected ticks.

Relapsing fever caused by lice (louse-borne relapsing fever)

Louse-borne relapsing fever is transmitted by infected body lice Body lice Lice infestation is a parasitic skin infestation caused by tiny wingless insects. Lice spread most frequently through close person-to-person contact. People with lice usually have severe itching... read more Body lice . A louse becomes infected when it feeds on a human host who is infected with a species of Borrelia. The louse spreads the bacteria to another person when it is crushed. The Borrelia bacteria are then released on to the person's skin. Once released, the bacteria can enter the person's body, usually through a bite or broken skin. Lice that have not been crushed do not transmit the infection.

This fever is rare in the United States and occurs mainly in the highlands of Central and East Africa and the Andes of South America. Louse-borne relapsing fever has also occurred in Europe in refugees from Africa. This fever tends to occur in epidemics, particularly in regions affected by war, and in refugee camps. The louse infestation is usually obvious.

Symptoms of Relapsing Fever

People with relapsing fever have sudden chills followed by a high fever, severe headache, vomiting, and muscle and joint pain. A thick, black, crusty scab (eschar) may form at the site of the tick bite. Some people have a reddish rash on the trunk and limbs and red eyes. Some people become delirious.

After several days, fever stops suddenly, and people feel better. However, the fever and usually the other symptoms return and go away (relapse) at about 1-week intervals for up to 30 episodes. The episodes become progressively less severe, and people eventually recover as they develop immunity to the disease.

Diagnosis of Relapsing Fever

  • Examination of a blood sample

Doctors suspect relapsing fever if people have recurring fevers, especially if they report spending the night in a cave or in a mountain cabin.

To diagnose relapsing fever, doctors take a sample of blood and examine it under a microscope to look for Borrelia bacteria. Measuring antibodies against the Borrelia bacteria that cause relapsing fever may help. Doctors measure them soon after the infection is diagnosed and again weeks after people have recovered. An increased amount of antibodies to Borrelia after recovery shows that Borrelia was the cause.

Prognosis for Relapsing Fever

Most people recover, but some die. Death is more likely in the very young, pregnant women, older people, people who are undernourished or debilitated, and those who are infected during an epidemic of louse-borne relapsing fever.

For louse-borne relapsing fever, death occurs in 10 to 40% of untreated people and in 2 to 5% of treated people.

For tick-borne relapsing fever, the prognosis is better. Death occurs in less than 10% of untreated people and in less than 2% of treated people.

Treatment of Relapsing Fever

  • Antibiotics

Antibiotics such as tetracycline, doxycycline, or erythromycin are usually effective.

Within 2 hours after the first dose of the antibiotic, an uncomfortable reaction called Jarisch-Herxheimer reaction Jarisch-Herxheimer reaction Syphilis is a sexually transmitted infection caused by the bacteria Treponema pallidum. It can occur in three stages of symptoms, separated by periods of apparent good health. Syphilis... read more Jarisch-Herxheimer reaction may occur, causing sweating, shaking chills, fever, and a fall in blood pressure. To reduce the severity of this reaction, doctors may give people acetaminophen before and after the first dose of the antibiotic. This reaction is not an allergic reaction to the antibiotic.

If people are dehydrated or have electrolyte imbalances because of vomiting, they are given fluids intravenously. Acetaminophen with oxycodone or hydrocodone may be given to relieve severe headaches, and prochlorperazine can relieve nausea and vomiting.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Centers for Disease Control and Prevention (CDC): Relapsing Fever: Information about relapsing fever, including links about transmission and symptoms

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