A 24-year-old man returns from trekking in the forests of Nagaland with high fever, headache and an eschar over his ankle. The laboratory reports a Weil-Felix reaction showing agglutination with the OXK strain of Proteus vulgaris at a titre of 1:320, while OX19 and OX2 are negative. The most likely diagnosis is:

• A Murine typhus due to Rickettsia typhi
• B Epidemic typhus due to Rickettsia prowazekii
• C Indian tick typhus due to Rickettsia conorii
• D Scrub typhus due to Orientia tsutsugamushi ✓

Explanation

In the Weil-Felix test, antibodies against rickettsiae cross-react with somatic antigens of Proteus strains. The OXK strain agglutinates specifically in scrub typhus (Orientia tsutsugamushi), while OX19 agglutinates in epidemic and murine typhus and OX2 in tick-borne spotted fevers. The presence of an eschar further supports Orientia infection. The tempting distractor, Rickettsia conorii, would show reactivity with OX19 and OX2 rather than OXK.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.