Which tick species is the vector for Rocky Mountain Spotted Fever?

• A. Dermacentor andersoni/variabilis
• B. Ixodes scapularis
• C. Amblyomma americanum
• D. Rhipicephalus sanguineus

Answer: (A)

Rocky Mountain Spotted Fever is caused by Rickettsia rickettsii and is transmitted to humans by Dermacentor ticks. In the United States, the classic vectors are Dermacentor variabilis (the American dog tick) in the eastern and southern regions and Dermacentor andersoni (the Rocky Mountain wood tick) in the western states. After the tick attaches and feeds for several hours, the bacteria are transmitted, leading to fever, headache, and a characteristic rash.

Other common ticks carry different pathogens and are not primary vectors for RMSF. Ixodes scapularis transmits Lyme disease (Borrelia burgdorferi), Amblyomma americanum is associated with ehrlichiosis, and Rhipicephalus sanguineus is linked to other rickettsial diseases—not RMSF in most U.S. settings.