Borrelia burgdorferi !
- Bacterium
- Does not Gram-stain
- Exam priority: medium
The spirochete of Lyme disease, spread by Ixodes ticks in North America and Europe; it is not endemic in Colombia.
Updated 2026-11-01
At a glance
- Gram
- Does not Gram-stain
- Shape
- Large spirochete with loose coils
- Oxygen
- Microaerophilic
- Family
- Borreliaceae
- Stain
- Stains weakly; Giemsa or silver in tissue (rarely seen)
Morphology
- Spirochete with endoflagella and a plasmid-rich genome
- Switches surface proteins (Osp) between tick and human
Transmission
- Bite of Ixodes (blacklegged) ticks, mainly nymphs
- The tick must stay attached for many hours to transmit it
Reservoir: White-footed mice and other small mammals; deer sustain the ticks
Vector: Ixodes scapularis and I. pacificus ticks (North America) and I. ricinus (Europe)
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Surface-protein variation to evade antibodies
- Spreads from skin to joints, heart and nervous system
- Host inflammation causes much of the joint damage
Diseases it causes
- Lyme disease: localised, early disseminated and late Lyme disease →
Clinical picture
- Erythema migrans: an expanding red patch, sometimes «bull's-eye»
- Early disseminated: facial palsy (sometimes bilateral), meningitis, atrioventricular block
- Late: arthritis of large joints, especially the knee
Diagnosis
- Erythema migrans with exposure in an endemic area is enough for a clinical diagnosis
- Two-tier serology (ELISA plus confirmation) in disseminated stages
- PCR on joint fluid in arthritis
Treatment
Doxycycline first; amoxicillin or cefuroxime are alternatives. Intravenous ceftriaxone is kept for severe neurological disease or advanced carditis.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Repellents, long clothing and body checks after walking in endemic woodland
- Remove attached ticks promptly
- Antibiotic prophylaxis after a high-risk bite in endemic areas
Test yourself
Think of the answer, then tap the question to see it.
Which skin lesion characterises early Lyme disease?
Erythema migrans, an expanding red patch from the bite site.
Which tick transmits B. burgdorferi?
Ixodes (blacklegged tick), mainly in its nymph stage.
Which cardiac problem can disseminated Lyme disease cause?
Atrioventricular block from Lyme carditis.
Related
- Borrelia recurrentis and tick-borne relapsing fever borreliae
- Ehrlichia / Anaplasma
- Treponema pallidum
Related conditions
← Back to the group: Spirochetes
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Lyme Disease | Lyme Disease | CDC (Centers for Disease Control and Prevention (CDC), 2024).
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Representative model, for educational purposes only.