A child from a rural forested area in Himachal Pradesh presents with 10 days of fever, an eschar on the neck, and cervical lymphadenopathy. Weil-Felix test shows agglutination of OX-K at 1:320 but not OX-19 or OX-2. Which pathogen is responsible?
- A Rickettsia rickettsii (Rocky Mountain spotted fever) transmitted by Dermacentor tick
- B Rickettsia typhi (murine typhus) transmitted by rat flea
- C Orientia tsutsugamushi (scrub typhus) transmitted by trombiculid mite larva (chigger) ✓
- D Bartonella henselae (cat scratch disease) transmitted by cat scratch/flea
Correct answer: C. Orientia tsutsugamushi (scrub typhus) transmitted by trombiculid mite larva (chigger)
Explanation
OX-K positive (Proteus mirabilis OX-K agglutination) in Weil-Felix test is characteristic of scrub typhus caused by Orientia tsutsugamushi (formerly Rickettsia tsutsugamushi). The eschar (tache noire — black painless necrotic eschar at the mite bite site) and regional lymphadenopathy are hallmarks. The vector is the larval stage (chigger) of trombiculid mites. OX-19 and OX-2 positive titers indicate typhus group (R. prowazekii, R. typhi) and spotted fever group (R. rickettsii) respectively.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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