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Bacteriology

Syphilis and Treponema pallidum

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SAMPLE QUESTION

Three weeks after a new sexual exposure, an adult develops a painless, clean-based ulcer with a firm border and nontender regional nodes. The lesion heals without treatment. Several weeks later, a diffuse rash involves the palms and soles, with generalized lymphadenopathy.

Which stage sequence and mechanism best explain these findings?