Balantidium: A genus of protozoa with cilia that includes Balantidium coli (B. coli). B. coli is the largest protozoan and the only ciliate parasite to infect humans. The disease that B. coli causes is called balantidiasis. Clinical features, when present, include persistent diarrhea, occasionally dysentery, abdominal pain, and weight loss. Symptoms can be severe in debilitated persons.

B. coli is found worldwide. Because pigs are an animal reservoir for B. coli, human infections occur more frequently in areas where pigs are raised. Other potential animal reservoirs include rodents and nonhuman primates. Humans most often acquire the disease through ingestion of contaminated food or water

Diagnosis is based on detection of the parasite in stool specimens or in tissue collected during endoscopy. B. coli is passed intermittently and once outside the colon is rapidly destroyed. Thus stool specimens should be collected repeatedly, and immediately examined or preserved to enhance detection of the parasite.

The drug of choice is tetracycline, with iodoquinol and metronidazole as alternatives. Tetracyclines are contraindicated in pregnancy and in children less than 8 years old.

From the Greek balantidion, meaning little bag.