Which organism causes giardiasis?

• A. Entamoeba histolytica
• B. Giardia lamblia
• C. Cryptosporidium parvum
• D. Ascaris lumbricoides

Answer: (B)

Giardia lamblia is the organism that causes giardiasis. It is a flagellated protozoan that you typically acquire by ingesting cysts in contaminated water or food. Once in the small intestine, the cysts release trophozoites that adhere to the intestinal mucosa, leading to malabsorption and the hallmark symptoms of giardiasis—greasy, foul-smelling diarrhea, bloating, and abdominal discomfort. Diagnosis is usually made by finding Giardia cysts or trophozoites in stool samples or by stool antigen testing.

Other organisms listed are responsible for different infections. Entamoeba histolytica causes amebic dysentery and liver abscess; Cryptosporidium parvum causes severe watery diarrhea especially in immunocompromised individuals; Ascaris lumbricoides is a parasitic worm that can cause intestinal obstruction and malnutrition.