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: Skin
[{'content': 'A young man presents to the emergency depament with a maculopapular rash 2 weeks after healing of a painless genital ulcer. The most likely etiological agent is: \nSelect and explain. \nA. Treponema Pallidum, B. Treponema Peunae, C. Chlamydia Trachomatis, D. Calymmatobacter granulomatis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Humans are the only natural reservoir of Treponema pallidum. It readily penetrates abraded skin and mucous membranes to multiply locally and spread through the blood stream or lymphatics. A developing maculopapular rash two weeks after a painless genital ulcer indicates a diagnosis of secondary syphillis. Ref: Primary care medicine: Office evaluation and management of the adult patient, by Allan H.Goroll,Albe G.Mulley, Page 989.', 'role': 'assistant'}]