It is estimated that fifty million people world-wide have this type of dysentery. it is contracted from contaminated water, and from fruits and vegetables grown in areas where human wastes are used as fertilizer. the protist enters through the mouth and eventually invades the walls of the intestines, causing ulcers and inflammation. this disease is caused by a protist, specifically a(n) a) algae. b) amoeba. c) euglena. d) paramecium.