Ascariasis is a parasitic infection caused by the roundworm Ascaris lumbricoides. It is transmitted via contaminated food or water (fecal-oral route), not through sexual contact. Explanation of other options:
(a) Hepatitis B is a viral infection that can be transmitted sexually — it is considered an STD.
(b) Syphilis is a bacterial STD caused by Treponema pallidum.
(c) Gonorrhea is a common STD caused by the bacterium Neisseria gonorrhoeae.