All life-sustaining processes occur in one cell. Except for some in wet soil, all protozoans occur in the aquatic environment. Causes Giardiasis, a gastrointestinal disease.
Ovoid cysts can survive in water for one to three months.
Humans become infected after ingesting as few as 10 cysts. Causes dysentary and ulceration of the colon and liver. E. hystolitica survives in an amoeboid form in the intestines. Spherical cysts are excreted in the feces. When ingested, an oocyst infects the cells of the digestive tract, epithelium, liver, kidneys, and blood.