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: Social & Preventive Medicine
Which group of organism is responsible for transmitting endemic typhus? 
Select and explain. 
A. Flea, B. Tick, C. Mite, D. Mosquito
A: Flea
Answer: A: Flea 
Explanation: The etiologic agent of endemic typhus (murine typhus fever or fleaborne typhus) is Rickettsia typhi, a Gram-negative bacterium and obligate intracellular pathogen. Reservoirs include rats, mice, possibly other mammals, and infected rat fleas. Endemic typhus has a worldwide occurrence.