## Eschar in Scrub Typhus **Key Point:** The eschar (tsutsugamushi lesion) is the pathognomonic finding in scrub typhus, present in 50–80% of cases. ### Characteristics of Eschar | Feature | Description | |---------|-------------| | **Appearance** | Black, necrotic, indurated papule | | **Surrounding** | Erythematous halo | | **Location** | Site of chigger (trombiculid mite) bite | | **Timing** | Appears 6–10 days after bite; persists 1–3 weeks | | **Painfulness** | Typically painless or mildly tender | | **Significance** | Highly specific for scrub typhus when present | **High-Yield:** The eschar is the clinical hallmark that distinguishes scrub typhus from other rickettsial diseases (RMSF does not produce an eschar; epidemic typhus does not produce an eschar). **Clinical Pearl:** Absence of eschar does NOT exclude scrub typhus—up to 50% of patients may lack a visible lesion, especially if the bite site is in an inconspicuous location (scalp, axilla, groin). ### Pathophysiology The eschar develops due to: 1. Direct inoculation of Orientia tsutsugamushi at the bite site 2. Local vasculitis and tissue necrosis 3. Inflammatory infiltrate with lymphocytes and macrophages 4. Central necrosis with black appearance (hence "black spot" or "tsutsugamushi") [cite:Park 26e Ch 3] 
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