This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Haemophilus, Yersinia, Spirochaetes, Ricketssia, Chlamydia, Mycoplasma and Miscellaneous Bacteria), Subject name: Microbiology
[{'content': 'Six days after receiving several flea bites in a rat-infested shed, a homeless 24-year-old-man develops fever, chills, and a rash that spreads from his abdomen to cover his extremities. He is seen at the hospital emergency depament, where blood is drawn for analysis. Eight days later, the public health depament repos the presence of antibody to one of the rickettsial group antigens. Which of the following is the most likely diagnosis? \nSelect and explain. \nA. Endemic typhus, B. Epidemic typhus, C. Q fever, D. Rocky Mountain spotted fever', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Endemic typhus Vector is flea Causative organism is R. typhi', 'role': 'assistant'}]