## Eschar in Scrub Typhus **Key Point:** The eschar is the pathognomonic lesion of scrub typhus, present in approximately 50–80% of cases. It develops at the site of the infected mite bite (chigger bite). ### Characteristics of Eschar - **Appearance:** Painless, necrotic ulcer with a black or dark brown crust (hence 'tache noire') - **Surrounding features:** Erythematous halo and induration - **Regional response:** Associated regional lymphadenopathy (often the first clinical sign) - **Timeline:** Appears 6–10 days after the bite, before systemic symptoms develop - **Significance:** When present, it is virtually diagnostic of scrub typhus ### Differential Eschar Presentations | Feature | Scrub Typhus (Orientia) | RMSF (Rickettsia rickettsii) | Tick Typhus (Rickettsia conorii) | | --- | --- | --- | --- | | Eschar | Present (50–80%) | Absent | Present (eschar at tick bite site) | | Rash onset | Day 5–7 | Day 2–4 | Day 5–7 | | Rash distribution | Trunk → limbs | Wrists/ankles → centripetal | Trunk + palms/soles | | Severity | Variable | Often severe | Moderate | **High-Yield:** The presence of an eschar with regional lymphadenopathy in a patient from endemic areas (Southeast Asia, especially India, Thailand, Laos) is virtually diagnostic of scrub typhus and warrants immediate empirical doxycycline therapy. **Clinical Pearl:** The eschar may be missed if it is in a hidden location (axilla, groin, scalp) or if the patient does not seek care early. [cite:Park 26e Ch 3] 
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