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
Endemic Typhus is caused by: 
Select and explain. 
A. R. Prowazaki, B. R. Typhi, C. R. Ricketssiae, D. R. Akari
B: R. Typhi
Answer: B: R. Typhi 
Explanation: R. Typhi