Balantidiasis is an infectious disease, rare in western countries. It is caused by Balantidium coli, a single celled parasite (ciliate protozoan) that is usually associated with intestinal infection in areas associated with pig rearing. It infects humans occasionally, mostly immunocompromised patients. Some infected people may have no symptoms or only mild diarrhea and abdominal discomfort but others may experience more severe symptoms reminiscent of an acute inflammation of the intestines. Symptoms of Balantidiasis may be similar to those of other infections that cause intestinal inflammation, for example, amoebic dysentery. On very rare occasions this bacterium may invade extra-intestinal organs, mostly the lungs. Metronidazole is the treatment of choice.