Scrub typhus is caused by Orientia tsutsugamushi. The diagnostic hallmark on clinical examination is:
- A Maculopapular rash starting on the trunk spreading centrifugally
- B Eschar (tache noire) at the site of chigger mite bite ✓
- C Rose spots on the abdomen
- D Petechiae and purpura in sun-exposed areas
Correct answer: B. Eschar (tache noire) at the site of chigger mite bite
Explanation
Eschar — a painless, necrotic, punched-out ulcer with a black crust — forms at the site where the trombiculid mite (chigger) larva fed and inoculated Orientia tsutsugamushi. It is found in 50–90% of cases (varies by geographic strain) and is pathognomonic when present. Common locations are axillae, groin, neck, and under belt lines (moist, dark areas). Weil-Felix OX-K agglutination titre ≥1:80 is a supportive but non-specific test. IgM ELISA and PCR of eschar swab are the preferred confirmatory tests.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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