[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/) › Orientia tsutsugamushi

[Microbiology](https://durgical.com/en/microbiology/) · [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

# Orientia tsutsugamushi

- Bacterium
- Gram-negative
- For completeness

A bacterium spread by mite larvae (chiggers) that causes scrub typhus, with a black scab at the bite site.

Updated 2026-11-01

Also called: scrub typhus

## Key points

- Black eschar + fever + lymph nodes in a traveller from Asia = scrub typhus
- Vector: mite larvae (chiggers)
- Doxycycline; azithromycin as an alternative

## At a glance

**Gram**
Gram-negative

**Shape**
Small coccobacillus

**Oxygen**
Obligate intracellular

**Family**
Rickettsiaceae

**Stain**
Stains poorly with Gram; Giemsa

## Morphology

- Formerly classed as Rickettsia; its wall lacks typical lipopolysaccharide and peptidoglycan
- Infects endothelial cells and macrophages

## Transmission

- Bite of trombiculid mite larvae (Leptotrombidium) in scrubland
- No person-to-person spread

**Reservoir:** The mites themselves (transovarial transmission) and rodents

**Vector:** Trombiculid mite larvae (chiggers)

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Vasculitis from endothelial infection, like rickettsiae
- Many antigenic strains: immunity after infection is short-lived

## Diseases it causes

- Scrub typhus

## Clinical picture

- Painless black eschar at the bite site
- Fever, headache, lymphadenopathy and truncal rash
- Complications: pneumonitis, meningoencephalitis, myocarditis

## Diagnosis

- Clinical: fever with an eschar after time in endemic rural areas
- Serology (IFA) or PCR of blood or the eschar

## Treatment

Doxycycline first; azithromycin in pregnancy and young children per clinical judgement.

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

In Pharmacology:

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)

## Prevention

- Repellents and long clothing in scrubland
- Vegetation and rodent control around homes

## In Colombia

Endemic in Asia and the Pacific; in South America, cases have been described in Chile from a related Orientia species. It is considered in travellers with fever and an eschar.

## Memory aid

In Japanese «tsutsuga» refers to illness and «mushi» to a bug: the tiny scrubland bug leaves its signature as a black scab.

## Test yourself

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

## Which vector transmits Orientia tsutsugamushi?

Larvae of trombiculid mites (chiggers) of the genus Leptotrombidium.

## Which skin lesion points to scrub typhus?

A painless black eschar at the bite site.

## What is the first-choice treatment for scrub typhus?

Doxycycline; azithromycin is an alternative.

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## Related

- [Rickettsia rickettsii / Rickettsia typhi](https://durgical.com/en/microbiology/rickettsia-rickettsii-rickettsia-typhi/)
- [Ehrlichia / Anaplasma](https://durgical.com/en/microbiology/ehrlichia-anaplasma/)

## 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: Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Typhus Fevers Basics | Typhus Fevers | CDC](https://www.cdc.gov/typhus/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024).

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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/orientia-tsutsugamushi/