Gram-negative obligately intracellular bacteria

Spotted fever group

Scrub typhus group

  • Scrub typhus (ST): Orientia tsutsugamushi (different strains/serotypes), Leptotrombidum mite

Typhus group

  • Epidemic typhus, Rickettsia prowazekii, Lice

  • Endemic typhus, murine typhus, Rickettsia typhi, Flea ()


Rickettsia endemic to Japan

  • JSF (April-October)

  • ST (Nov-Dec)

Reference: Distinguishing Japanese Spotted Fever and Scrub Typhus, Central Japan, 2004-2015


  • Fever

  • Rash (non-specific, macular popular)

  • Eschar: most pathognomonic sign of scrub typhus is the presence of an eschar, which is variously described as a black-crusted lesion or a cigarette burn-like lesion or a black necrotic lesion. The eschar represents the site of inoculation, where initial multiplication occurs before widespread dissemination

  • Breathing difficulty (low O2, ARDS)

  • CNS (meningitis)

  • Multi-organ failure

Differential Diagnosis

  • Dengue

  • Typhoid

  • Meiliod

  • Pneumonia?


Challenging (gold standard IFA + PCR?)

  • Antibody: Immunofluorescent assay (IFA) and others Enzyme-linked immunosorbent assay (ELISA) (e.g. InBios IgM detection combined 3 antigens Kato, Gilliam, TA763), Weil Felix reaction (low sens/spec)

  • Nucleic acid detection: PCR (conventional, nested, real-time) Loop-mediated isothermal amplification (LAMP) PCR of eschar tissue

  • Antigen detection: culture requires BSL3, PCR

  • Isolation: Cell culture, Mouse inoculation


  • Antibiotics: Doxycycline

  • Antipyretic