A 35 year old man who recently traveled to a third world country develops chronic, severe dysentery. Colonoscopy demonstrates ulceration of the cecum, and a cecal biopsy reveals 15-to-40 micron amoebae with ingested erythrocytes and small nuclei with distinctive tiny central karyosomes. Which of the following organisms is the most likely culprit?
Acanthamoeba sp Balantidium coli Entamoeba histolytica Giardia lamblia