Relapsing Fever – A Complete Guide

What is Relapsing fever?

Relapsing fever is a group of bacterial infections characterized by recurring episodes of high fever, chills, headache, muscle pain, and general malaise. The fever spikes last several days, subside for a few days to a week (the “remission” period), and then return—sometimes several times before the illness resolves or is treated.

The disease is caused by spirochete bacteria of the genus Borrelia. These organisms are transmitted to humans through the bite of infected arthropod vectors—most commonly soft ticks (Ornithodoros spp.) or body lice (Pediculus humanus corporis). Because the bacteria can hide in the bloodstream and change their surface proteins, the immune system may clear one strain only to be attacked by a slightly different one, producing the classic relapsing pattern.

Relapsing fever occurs worldwide but is most prevalent in sub‑Saharan Africa, Central and South America, and parts of Asia where the vectors thrive in rural or peri‑urban settings.

Common Causes

The term “relapsing fever” encompasses several distinct infections. Below are the most common etiologic agents and the contexts in which they are transmitted:

• Tick‑borne relapsing fever (TBRF) – Caused by Borrelia species such as B. recurrentis, B. hermsii, B. duttonii, B. turicatae, and B. miyamotoi. Transmitted by soft ticks (Ornithodoros).
• Louse‑borne relapsing fever (LBRF) – Primarily caused by B. recurrentis and spread by the human body louse.
• Sepsis‑related relapsing fevers – Rarely, other spirochetes (e.g., Treponema pallidum in early syphilis) can mimic the pattern.
• Endemic areas with rodent reservoirs – Species such as B. crocidurae in West Africa are maintained in rodent‑tick cycles.
• Travel‑associated exposure – Visiting caves, cabins, or historic homes infested with soft ticks.
• Crowded or unhygienic living conditions – Overcrowding facilitates louse infestations.
• Occupational exposure – Farmers, park rangers, and researchers working in tick‑infested habitats.
• Immunocompromised status – HIV, transplant recipients, or patients on chronic steroids may have atypical or prolonged courses.
• Co‑infection with other vector‑borne diseases – Tick bites may also transmit Rickettsia or Babesia, complicating the picture.
• Inadequate treatment of a previous episode – Incomplete antibiotic courses can lead to relapse.

Associated Symptoms

While the hallmark of relapsing fever is the cyclical fever itself, patients often experience a constellation of other signs and symptoms that may vary in intensity between episodes:

• High fever (usually 38‑41 °C / 100‑106 °F) lasting 3‑7 days
• Severe chills and rigors at the onset of each febrile episode
• Headache, often described as “throbbing” or “migraine‑like”
• Muscle and joint aches (myalgia, arthralgia)
• Generalized weakness and fatigue
• Nausea, vomiting, or loss of appetite
• Rash – maculopapular or petechial, more common in LBRF
• Abdominal pain or mild hepatosplenomegaly
• Neurologic signs (confusion, meningismus) in severe or untreated cases
• Jaundice or hemolytic anemia (particularly with B. duttonii)

Because the fever recurs, patients may mistakenly think they have multiple unrelated infections, which can delay proper diagnosis.

When to See a Doctor

Relapsing fever can be self‑limited, but early medical evaluation is crucial to prevent complications such as severe anemia, organ failure, or neurologic involvement. Seek professional care if you experience any of the following:

• Fever that rises above 38 °C (100 °F) and recurs after a symptom‑free interval
• Recent travel to, or residence in, an area known for tick‑borne or louse‑borne relapsing fever
• History of a tick or louse bite, especially in rural cabins, caves, or crowded living spaces
• New or worsening rash, especially petechiae (small red spots)
• Persistent vomiting, severe abdominal pain, or dark urine (possible hemolysis)
• Neurologic symptoms such as severe headache, confusion, stiff neck, or seizures
• Signs of dehydration (dry mouth, dizziness, reduced urine output)

Diagnosis

Diagnosing relapsing fever relies on a combination of clinical suspicion and laboratory testing.

Clinical Evaluation

• Detailed travel, occupational, and exposure history
• Physical examination focusing on rash, lymphadenopathy, hepatosplenomegaly, and neurologic status

Laboratory Tests

• Blood smear (dark‑field microscopy) – Direct visualization of motile spirochetes during a febrile episode is the classic method.
• Polymerase Chain Reaction (PCR) – Detects Borrelia DNA in blood; more sensitive than microscopy, especially after antibiotics have begun.
• Serologic testing – Enzyme‑linked immunosorbent assay (ELISA) and indirect immunofluorescence can identify antibodies, but results may lag behind clinical presentation.
• Complete blood count (CBC) – May reveal anemia, thrombocytopenia, or leukopenia.
• Liver function tests – Elevated transaminases or bilirubin if hepatic involvement.
• Renal panel – To assess for acute kidney injury in severe disease.

Timing of Tests

Because spirochetemia is intermittent, a negative blood smear does not exclude the disease. Repeat testing during a fever spike dramatically improves the yield.

Differential Diagnosis

Conditions that can mimic relapsing fever include malaria, typhoid fever, dengue, viral hepatitis, Q fever, and acute HIV infection. A thorough work‑up helps to rule out these possibilities.

Treatment Options

Prompt antibiotic therapy shortens the illness, prevents relapses, and reduces the risk of serious complications.

First‑line Antibiotics

• Doxycycline – 100 mg orally twice daily for 7‑10 days (or a single 200 mg dose for mild disease).
• Tetracycline – 500 mg orally four times daily for 7‑10 days (alternative if doxycycline unavailable).
• Penicillin G – 3‑6 million units IV every 4‑6 hours for severe infection.
• Ceftriaxone – 1‑2 g IV daily for patients allergic to penicillin or with central nervous system involvement.

These regimens are supported by the WHO and CDC guidelines for both TBRF and LBRF.^[1][2]

Jarisch‑Herxheimer Reaction

Within the first hour of antibiotic initiation, up to 25 % of patients develop a sudden fever spike, chills, tachycardia, and hypotension—known as the Jarisch‑Herxheimer reaction. This is a transient inflammatory response to bacterial endotoxin release. Management includes:

• Monitoring vital signs closely for at least 2 hours after the first dose.
• Administering antipyretics (acetaminophen or ibuprofen).
• Ensuring adequate hydration.
• In severe cases, brief use of low‑dose corticosteroids (under physician supervision).

Supportive Care

• Oral or IV rehydration to correct fluid loss from fever and vomiting.
• Analgesics/antipyretics for headache and muscle aches.
• Rest and nutritional support; small, frequent meals are easier to tolerate.
• Monitoring for anemia; transfusion may be required in profound cases.

Special Populations

• Pregnant women – Erythromycin 500 mg orally four times daily for 7‑10 days is preferred.
• Children & infants – Doxycycline is avoided under 8 years; use penicillin G or ceftriaxone instead.
• Immunocompromised patients – Longer courses (up to 14 days) and close follow‑up are recommended.

Prevention Tips

Because relapsing fever is vector‑borne, preventive measures focus on reducing exposure to ticks and lice.

• Wear protective clothing – Long sleeves, long pants, and closed shoes when entering tick‑infested areas.
• Use insect repellent – Apply EPA‑registered products containing 20‑30 % DEET, picaridin, or IR3535 to skin and clothing.
• Inspect and shower – After outdoor activities, examine the entire body for ticks and wash promptly.
• Improve living conditions – Regular laundering of bedding and clothing, and prompt removal of body lice with medicated shampoos (e.g., permethrin 1 %).
• Rodent control – Seal cracks in homes, store food in hard‑covered containers, and use traps in endemic rural settings.
• Environmental management – Keep cabins and caves dry; soft ticks prefer humid, protected crevices.
• Travel preparation – Consult travel clinics for prophylactic advice when visiting high‑risk regions.
• Vaccines – No vaccine currently exists for relapsing fever; prevention relies on vector control.

Emergency Warning Signs

Key Take‑aways

• Relapsing fever is caused by Borrelia spirochetes transmitted by soft ticks or body lice.
• The illness is marked by recurring fevers, headache, muscle pain, and sometimes rash or neurologic signs.
• Prompt diagnosis (blood smear or PCR) and treatment with doxycycline, tetracycline, or penicillin are essential.
• Preventing tick and louse exposure, especially in endemic regions, dramatically reduces risk.
• Emergency warning signs require immediate medical attention.

References:
[1] Centers for Disease Control and Prevention. “Relapsing Fever.” https://www.cdc.gov/relapsingfever (accessed May 2026).
[2] World Health Organization. “Tick‑borne Relapsing Fever.” https://www.who.int (accessed May 2026).
[3] Mayo Clinic. “Relapsing Fever – Symptoms and Causes.” https://www.mayoclinic.org (accessed May 2026).
[4] Cleveland Clinic. “Management of Tick‑borne Diseases.” https://my.clevelandclinic.org (accessed May 2026).
[5] National Institute of Allergy and Infectious Diseases. “Borrelia Infections.” https://www.niaid.nih.gov (accessed May 2026).