[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Spirochetes](https://durgical.com/en/microbiology/groups/spirochetes/) › Borrelia burgdorferi

[Microbiology](https://durgical.com/en/microbiology/) · [Spirochetes](https://durgical.com/en/microbiology/groups/spirochetes/)

# 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

## Key points

- Erythema migrans = clinical diagnosis, no need to wait for serology
- Bilateral facial palsy + AV block in an endemic area: think Lyme
- Ixodes vector, mouse reservoir, deer sustain the tick
- Ixodes also transmits Anaplasma and Babesia (coinfections)

## 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 →](https://durgical.com/en/conditions/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:

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Amoxicillin](https://durgical.com/en/pharmacology/amoxicillin/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)

## 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

## In Colombia

Not endemic in Colombia; it is considered in travellers returning from North America or Europe. It is a frequent USMLE topic.

## Memory aid

Lyme draws a «target» on the skin, then aims at the face (palsy), the heart (block) and finally the knee.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/borrelia-burgdorferi/)

## Related

- [Borrelia recurrentis and tick-borne relapsing fever borreliae](https://durgical.com/en/microbiology/borrelia-recurrentis-and-tick-borne-relapsing-fever-borreliae/)
- [Ehrlichia / Anaplasma](https://durgical.com/en/microbiology/ehrlichia-anaplasma/)
- [Treponema pallidum](https://durgical.com/en/microbiology/treponema-pallidum/)

## Related conditions

- [Lyme disease](https://durgical.com/en/conditions/lyme-disease/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Spirochetes](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/lyme/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/borrelia-burgdorferi/