Treponema pallidum — Syphilis

Which of the following is the most characteristic morphological feature of Treponema pallidum that distinguishes it from other spirochetes?

A 28-year-old man from Mumbai presents to the STI clinic with a painless ulcer on the glans penis for 3 weeks. He reports a single sexual contact 4 weeks ago. On examination, the ulcer has a well-demarcated border, indurated base, and is non-purulent. Regional lymph nodes are enlarged, firm, and non-tender. Serum RPR is positive (1:16) and FTA-ABS is positive. Dark-field microscopy of ulcer exudate shows motile, spiral organisms. What is the most appropriate next step in management?

A 28-year-old man presents with a painless ulcer on the glans penis for 3 weeks. Examination reveals a single indurated ulcer with a clean base and raised borders. Regional lymph nodes are enlarged and non-tender. Which investigation is most appropriate to confirm the diagnosis of primary syphilis?

A 28-year-old man from Mumbai presents with a painless ulcer on the glans penis for 3 weeks. He reports unprotected sexual contact 4 weeks ago. On examination, the ulcer has a clean base with indurated edges and regional lymphadenopathy. Serological tests show positive RPR (1:32) and positive FTA-ABS. What is the most appropriate next step in management?

A 35-year-old woman from Delhi presents with a 2-month history of fever, malaise, and a maculopapular rash on her trunk and palms. She reports a painless genital ulcer that healed spontaneously 8 weeks ago. Examination reveals generalized lymphadenopathy, hepatosplenomegaly, and condylomata lata in the perianal region. RPR is positive (1:64), FTA-ABS is positive, and CSF examination is normal. What is the most likely diagnosis?