Rocky Mountain Spotted Fever is caused by which organism?

Rocky Mountain Spotted Fever is caused by which organism?

• A. Borrelia burgdorferi
• B. Rickettsia rickettsii
• C. Ehrlichia chaffeensis
• D. Yersinia pestis

Answer: (B)

Rocky Mountain Spotted Fever is caused by Rickettsia rickettsii, a gram-negative, obligate intracellular bacterium transmitted by hard ticks (notably Dermacentor species). The infection targets vascular endothelium, leading to vasculitis that produces fever, headache, and a rash that often starts on the wrists and ankles before spreading to the trunk. This organism is distinct from others listed: Borrelia burgdorferi causes Lyme disease and is transmitted by Ixodes ticks with a different clinical pattern (erythema migrans and migratory symptoms); Ehrlichia chaffeensis causes ehrlichiosis with fever and cytopenias and a different vector; Yersinia pestis causes plague transmitted by fleas and presents with buboes and severe systemic illness.

Rocky Mountain Spotted Fever is caused by Rickettsia rickettsii, a gram-negative, obligate intracellular bacterium transmitted by hard ticks (notably Dermacentor species). The infection targets vascular endothelium, leading to vasculitis that produces fever, headache, and a rash that often starts on the wrists and ankles before spreading to the trunk. This organism is distinct from others listed: Borrelia burgdorferi causes Lyme disease and is transmitted by Ixodes ticks with a different clinical pattern (erythema migrans and migratory symptoms); Ehrlichia chaffeensis causes ehrlichiosis with fever and cytopenias and a different vector; Yersinia pestis causes plague transmitted by fleas and presents with buboes and severe systemic illness.