Conditions · Infectious and tropical diseases
Relapsing fever (tick-borne and louse-borne borreliosis) !
Relapsing fever is a Borrelia infection spread by ticks or body lice, with bouts of high fever that come back again after days without fever.
Updated 2026-11-01
Structures involved
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Microorganisms that cause it
Why it happens
- Systemic effects of inflammation: fever, acute-phase proteins, leukocytosis, sepsis
- Fever
- Innate and adaptive immunity: overview
What it is
An infection by Borrelia spirochaetes that causes repeated episodes of high fever separated by afebrile periods of about a week. It is transmitted by soft ticks (endemic, tick-borne) or by body lice (epidemic, louse-borne). The spirochaetes can be seen directly in a blood smear during fever.
Who gets it
Tick-borne relapsing fever occurs in the Americas, Africa, the Middle East, Asia and Europe, often in rural houses, caves or cabins where rodents and soft ticks live. In Mexico, Central and South America species such as Borrelia venezuelensis have been described, but the disease is rarely diagnosed, and the spirochaetes may first be noticed on a smear taken to look for malaria. Louse-borne relapsing fever now occurs mainly in the Horn of Africa and among displaced people and migrants living in crowded conditions.
Causes
- Tick-borne: many Borrelia species carried by soft ticks (Ornithodoros), which feed briefly and painlessly at night
- Hard tick-borne relapsing fever: Borrelia miyamotoi
- Louse-borne: Borrelia recurrentis, spread when crushed body lice contaminate skin breaks
- Incubation about one week
Risk factors
- Sleeping in rustic, rodent-infested houses, cabins or caves
- Body lice infestation in crowding, poverty, war or migration
- Travel to endemic areas of Africa
- Pregnancy (more severe disease and risk to the fetus)
Pathophysiology
Spirochaetes multiply in the blood to high numbers, causing fever. Antibodies clear them, the fever ends in a crisis, and the patient feels well for several days. A few bacteria switch their surface proteins (antigenic variation) and escape, starting the next episode. Each relapse is usually milder. Spirochaetes lodge in the spleen, liver, brain, eye and heart, causing organ damage, thrombocytopenia and bleeding. Killing many spirochaetes at once with antibiotics releases inflammatory mediators (Jarisch-Herxheimer reaction).
Classification
- Soft tick-borne (endemic): several relapses
- Hard tick-borne (B. miyamotoi): usually milder, fewer relapses
- Louse-borne (epidemic): usually one or two relapses, more severe
Symptoms and signs
- Sudden high fever with rigors, headache, muscle and joint pain lasting several days
- Fever that ends abruptly and returns after about a week of feeling well
- Enlarged, tender liver and spleen, jaundice
- Petechiae, nosebleeds and other bleeding
- Cough, confusion, neck stiffness, facial palsy or eye inflammation in some patients
Diagnosis
- Clinical
- Suspected from recurrent fevers with symptom-free gaps and an exposure history: rustic sleeping places, caves, lice or travel. A detailed fever pattern helps distinguish it from malaria and other febrile illnesses.
- Tests
- Thick and thin blood smears (Giemsa or Wright) taken during fever show spirochaetes; PCR is more sensitive and works between episodes; serology may cross-react with Lyme disease. Blood tests: thrombocytopenia, raised bilirubin and liver enzymes, mild coagulation changes.
- Imaging
- Not needed for diagnosis; abdominal ultrasound may show splenomegaly.
Differential diagnosis
- Malaria (recurring fevers; both found on blood smear)
- Leptospirosis
- Typhoid fever and rickettsial infections
- Dengue and other arboviral infections
- Lyme disease and other borrelioses
Goal of treatment
Kill the spirochaetes and stop relapses while anticipating and managing the Jarisch-Herxheimer reaction, and remove lice or ticks to prevent new cases.
Treatment
- Medical
- A tetracycline (doxycycline) is preferred; alternatives are a macrolide (azithromycin) or a beta-lactam (penicillin or ceftriaxone), which is chosen in pregnancy and young children. Louse-borne disease may be cured with a single dose.
- Follow-up
- Close observation of vital signs for at least the first 4 hours after the first antibiotic dose to detect the Jarisch-Herxheimer reaction.
- Acute
- Treatment of the Jarisch-Herxheimer reaction with intravenous fluids, antipyretics and support of blood pressure; intensive care for ARDS, bleeding or myocarditis.
- Lifestyle
- Delousing with clothing and bedding changes and hot washing for louse-borne disease; rodent-proofing and tick control in dwellings.
Complications
- Jarisch-Herxheimer reaction with shock
- Myocarditis and arrhythmias
- Meningitis, cranial nerve palsy and iritis
- Bleeding and splenic rupture
- Miscarriage, stillbirth and neonatal infection
- ARDS
Prognosis
With treatment, mortality is low. Untreated louse-borne relapsing fever can kill a large share of patients during epidemics; deaths also occur from the Jarisch-Herxheimer reaction, myocarditis and bleeding.
Prevention
- Rodent-proofing houses and cabins and avoiding sleeping in caves
- Personal hygiene and laundering to control body lice in shelters and camps
- Insect repellents and protective clothing
Test yourself
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How is relapsing fever diagnosed at the bedside?
By seeing spirochaetes on a thick or thin blood smear taken during a fever episode.
What explains the relapses?
Antigenic variation of Borrelia surface proteins, which lets bacteria escape the antibody response.
What reaction must be watched for after the first antibiotic dose?
The Jarisch-Herxheimer reaction: rigors, high fever and hypotension within hours.
Which vector transmits Borrelia recurrentis?
The human body louse.
Related conditions
- Malaria
- Lyme disease
- Leptospirosis
- Typhoid (enteric) fever
- Rickettsial infections (spotted fever)
- Dengue
- Myocarditis
- Acute respiratory distress syndrome (ARDS)
- Pediculosis (head, body and pubic lice)
- Sepsis and septic shock
Educational information, not medical advice. For any symptom, see a health professional.
Sources: About Tick and Louse-borne Relapsing Fevers | Tick and Louse-borne Relapsing Fevers | CDC (Centers for Disease Control and Prevention, 2024); Clinical Guidance for Soft Tick Relapsing Fever (STRF) (Centers for Disease Control and Prevention, 2024); Clinical Guidance for Louse-borne Relapsing Fever (LBRF) (Centers for Disease Control and Prevention, 2024).
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