Microbiology · 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
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:
Prevention
- Repellents and long clothing in scrubland
- Vegetation and rodent control around homes
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.
Related
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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 (Centers for Disease Control and Prevention (CDC), 2024).
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Representative model, for educational purposes only.