Trichomonas vaginalis is an STD protozoan that causes frothy yellow-green discharge and has flagellated motility. Which option lists the correct organism?

• A. Giardia lamblia
• B. Toxoplasma gondii
• C. Plasmodium falciparum
• D. Trichomonas vaginalis

Answer: (D)

This question tests recognizing a sexually transmitted protozoan that causes a frothy yellow-green vaginal discharge with visible flagellated motility. The organism that matches this description is Trichomonas vaginalis, a flagellated protozoan that parasitizes the urogenital tract and is transmitted through sexual contact. Diagnosis is often made by observing motile protozoa on a saline or wet mount of vaginal discharge. The other organisms listed are not associated with this presentation: Giardia lamblia causes gastrointestinal disease from fecal-oral transmission; Toxoplasma gondii is an intracellular parasite acquired from cat feces or undercooked meat with systemic or congenital disease; Plasmodium falciparum causes malaria transmitted by mosquitoes.