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Balantidium coli, though rare in the US, is an intestinal protozoan parasite that can infect humans. These parasites can be transmitted through the fecal-oral route by contaminated food and water. Balantidium coli infection is mostly asymptomatic, but people with other serious illnesses can experience persistent diarrhea, abdominal pain, and sometimes a perforated colon. When traveling to endemic tropical countries, Balantidium coli infection can be prevented by following good hygiene practices. Wash all fruits and vegetables with clean water when preparing or eating them, even if they have a removable skin.

Image: Left: Balantidium coli cyst. Right: B. coli trophozoite in a wet mount at 1000x magnification. Credit: PHIL, Oregon Public Health Laboratory.