Final answer:
The causative agent for Rocky Mountain Spotted Fever is (D) Rickettsia rickettsii, which is an obligate intracellular parasite transmitted to humans via the bite of an infected tick.
Step-by-step explanation:
The causative agent for Rocky Mountain Spotted Fever (RMSF) is Rickettsia rickettsii. RMSF is transmitted to humans through the bite of infected hard-bodied ticks such as the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (D. andersoni), or brown dog tick (Rhipicephalus sanguineus). However, the actual pathogen that causes the disease is the obligate intracellular parasite Rickettsia rickettsii, not the ticks themselves which are merely vectors.
Rickettsia rickettsii is responsible for causing a life-threatening form of meningoencephalitis and is known for producing a petechial rash that begins at the hands and wrists before spreading to the trunk. Effective diagnosis and management of tickborne rickettsial diseases are crucial for public health.