A 30-year-old man from Andhra Pradesh presents with fever for 10 days, headache, generalised rash that started on the trunk and spread to limbs, and a necrotic eschar on the right groin with regional lymphadenopathy. Weil-Felix test shows agglutination with OX2 antigen. The causative organism is:
- A Rickettsia prowazekii (epidemic typhus)
- B Rickettsia conorii (Mediterranean spotted fever/Indian tick typhus) ✓
- C Orientia tsutsugamushi (scrub typhus)
- D Rickettsia typhi (murine/endemic typhus)
Explanation
The clinical picture describes Indian tick typhus (Mediterranean spotted fever) caused by Rickettsia conorii, transmitted by the dog tick Rhipicephalus sanguineus. Key features: eschar (tache noire) at tick bite site, maculopapular rash centripetal (trunk to periphery, including palms and soles), and Weil-Felix OX2 positivity. OX2 (+), OX19 (+), OXK (−). Scrub typhus (Orientia tsutsugamushi) gives OXK positivity (not OX2). Epidemic typhus (R. prowazekii, body louse-borne) gives OX19 > OX2 positivity. Murine typhus (R. typhi, flea-borne) gives OX19 positivity. Treatment for all rickettsiae is doxycycline.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.