Which organism is most closely associated with giardiasis?

• A. Giardia Intestinalis
• B. Trichomonas vaginalis
• C. Plasmodium species
• D. Schistosoma mansoni

Answer: (A)

Giardiasis is caused by a flagellated protozoan that infects the small intestine after ingesting cysts from contaminated water or food. The organism responsible is Giardia intestinalis (also called Giardia lamblia). It forms environmentally resistant cysts that survive stomach acid and release trophozoites in the intestine, leading to diarrhea, malabsorption, and greasy stools. Among the options, only Giardia intestinalis is linked to giardiasis; the others cause different diseases—Trichomonas vaginalis causes trichomoniasis, Plasmodium species cause malaria, and Schistosoma mansoni causes schistosomiasis. So Giardia intestinalis is the best answer because it is the direct etiologic agent of giardiasis.