A 35-year-old from Himachal Pradesh presents with sudden-onset fever, severe headache, and an eschar (tache noire) on the ankle with regional lymphadenopathy. Serology by Weil-Felix test shows agglutination with OX2 proteus antigen but not OX19 or OXK. The most likely diagnosis is:
- A Indian tick typhus (Rickettsia conorii) ✓
- B Scrub typhus (Orientia tsutsugamushi)
- C Epidemic typhus (Rickettsia prowazekii)
- D Murine typhus (Rickettsia typhi)
Correct answer: A. Indian tick typhus (Rickettsia conorii)
Explanation
Indian tick typhus (Mediterranean/Indian spotted fever) is caused by Rickettsia conorii, transmitted by Rhipicephalus sanguineus tick bite; the eschar (tache noire) at the bite site is characteristic. The Weil-Felix test for R. conorii shows agglutination with OX2 (high titer) and variable OX19, but NOT OXK. Scrub typhus (Orientia tsutsugamushi) agglutinates OXK only. Epidemic typhus (R. prowazekii) agglutinates OX19 and OX2. The preferred treatment for all rickettsial diseases 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.