[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 recurrentis and tick-borne relapsing fever borreliae

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

# Borrelia recurrentis and tick-borne relapsing fever borreliae

- Bacterium
- Does not Gram-stain
- For completeness

Borreliae spread by lice or soft ticks that cause fevers that come and go for weeks.

Updated 2026-11-01

Also called: relapsing fever

## Key points

- The only spirochete easily seen on a blood smear
- Fever that comes and goes because of antigenic variation
- Jarisch-Herxheimer very common on treatment

## At a glance

**Gram**
Does not Gram-stain

**Shape**
Large spirochete with loose coils

**Oxygen**
Microaerophilic

**Family**
Borreliaceae

**Stain**
Visible on Giemsa- or Wright-stained blood smear during fever

## Morphology

- Spirochetes between red cells on the blood smear
- Change their main surface protein at each relapse

## Transmission

- B. recurrentis: body louse, crushed into broken skin (not by the bite)
- Other species (such as B. hermsii): brief bite of Ornithodoros soft ticks, often at night in cabins
- Some hard ticks transmit B. miyamotoi

**Reservoir:** B. recurrentis: humans only; Tick-borne species: wild rodents

**Vector:** Body louse (Pediculus humanus corporis) or Ornithodoros soft ticks

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Antigenic variation: each new variant causes a new fever spike
- High blood load during fever

## Diseases it causes

- Epidemic (louse-borne) and endemic (tick-borne) relapsing fever [Relapsing fever (tick-borne and louse-borne borreliosis) →](https://durgical.com/en/conditions/relapsing-fever/)

## Clinical picture

- Bouts of high fever, headache and myalgia lasting days, separated by symptom-free days
- Hepatosplenomegaly, jaundice and neurological involvement may occur
- The louse-borne form is more severe and appears with crowding, war and refugee camps

## Diagnosis

- Peripheral blood smear taken during fever (thick or thin film)
- PCR when available

## Treatment

Tetracyclines (doxycycline) or macrolides (erythromycin); penicillin or ceftriaxone with neurological involvement. The Jarisch-Herxheimer reaction is common and intense when the antibiotic starts and requires monitoring.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Erythromycin](https://durgical.com/en/pharmacology/erythromycin/)
- [Benzylpenicillin (penicillin G)](https://durgical.com/en/pharmacology/benzylpenicillin/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)

## Prevention

- Louse control: personal hygiene, washing clothes in hot water
- Rodent-proof cabins in soft-tick areas

## Memory aid

This borrelia «changes costume» every week: when the body learns to spot it, it debuts a new protein and the fever comes back.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does relapsing fever cause repeated fever bouts?

Because the bacterium changes its surface proteins (antigenic variation) and escapes antibodies.

## What is the simplest way to diagnose relapsing fever?

A Giemsa- or Wright-stained blood smear taken during a fever spike.

## Which vector transmits B. recurrentis?

The body louse; the bacterium enters when the louse is crushed on the skin.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/borrelia-recurrentis-and-tick-borne-relapsing-fever-borreliae/)

## Related

- [Borrelia burgdorferi](https://durgical.com/en/microbiology/borrelia-burgdorferi/)
- [Leptospira interrogans](https://durgical.com/en/microbiology/leptospira-interrogans/)

## Related conditions

- [Relapsing fever (tick-borne and louse-borne borreliosis)](https://durgical.com/en/conditions/relapsing-fever/)

## 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 Tick and Louse-borne Relapsing Fevers](https://www.cdc.gov/relapsing-fever/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024); [Typhus Fevers Basics | Typhus Fevers | CDC](https://www.cdc.gov/typhus/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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Source: https://durgical.com/en/microbiology/borrelia-recurrentis-and-tick-borne-relapsing-fever-borreliae/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/borrelia-recurrentis-and-tick-borne-relapsing-fever-borreliae/