A 30-year-old man from Himachal Pradesh develops fever, myalgia, and a petechial rash involving the palms and soles after a tick bite. Biopsy of a skin lesion would show the organism within which cells?

• A Neutrophils in the dermal infiltrate
• B Endothelial cells of small blood vessels ✓
• C Macrophages of the reticuloendothelial system
• D Keratinocytes of the basal layer

Explanation

Rickettsia rickettsii, the agent of Indian tick typhus and Rocky Mountain spotted fever, invades and multiplies within endothelial cells lining small vessels, producing endothelial swelling, thrombosis, perivascular lymphocytic infiltration, and the characteristic vasculitic rash that involves palms and soles. Macrophage tropism is typical of Coxiella and Ehrlichia, neutrophil tropism of Ehrlichia ewingii, and keratinocyte involvement is not a feature of any rickettsial infection.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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