Syphilis is a complex systemic sexually transmitted infection caused by–

Correct option is D

Sol. Syphilis is caused by the bacterium Treponema pallidum, which is a type of spirochete (spiral-shaped bacteria). It spreads primarily through sexual contact and can affect multiple organs over time if left untreated. It is curable with antibiotics like penicillin.
Explanation of each option:
· (a) A helminth – Helminths are parasitic worms and do not cause syphilis. They cause diseases like filariasis and ascariasis.
· (b) A fungus – Fungal infections include candidiasis or ringworm, not syphilis, which is bacterial.
· (c) A virus – Viral STIs include HIV, HPV, and Herpes, not syphilis.
· (d) A spirochete – Correct answer. Syphilis is caused by Treponema pallidum, which is a spiral-shaped bacterium.