This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Most serious form of Rickettsial disease - 
Select and explain. 
A. Scrub typhus, B. Q-fever, C. Trench fever, D. Rocky mountain spotted fever
D: Rocky mountain spotted fever
Answer: D: Rocky mountain spotted fever 
Explanation: Ans. is 'd' i.e.,Rocky mountain spotted fever "Among the Rickettsial diseases, Rocky mountain spotted fever is the most common and the most serious"The microbial chalonge "R rickettsii (causative agent of RMSF) is the most virulent Rickettsia" -- Clinical microbiology