Balantidium coli

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Balantidium coli is a species of ciliate protozoan. This parasite is the only member of this family known to be pathogenic to humans. Hosts include pigs, wild boars, rats, primates (including humans), horses, cattle and guinea pigs. Infection is transmitted within or between these species by fecal-oral transmission. Pigs are the most significant reservoir hosts, though they show few if any symptoms.

Cysts are the infective stage, responsible for transmission of balantidiasis. The host usually acquires cysts through ingestion of contaminated food or water. Following ingestion, excystation occurs in the small intestine, and the trophozoites colonize the large intestine. Both cysts and trophozoites are identifiable by a large, "sausage shaped" macronucleus.

Balantidium coli as seen in a wet mount of a stool specimen. The organism is surrounded by cilia

The trophozoites reside in the lumen of the large intestine, where they replicate by transverse binary fission, during which conjugation may occur. Some trophozoites invade the wall of the colon using proteolytic enzymes and multiply; some of these return to the lumen. In the lumen Trophozoites may disintegrate or undergo encystation. Encystation is trigerred by dehydration of the intestinal contents and usually occurs in the distal large intestine, but may also occur outside of the host in feces. Symptoms can be local due to involvement of the intestinal mucosa, or systemic in nature and include diarrhea. Balantidiasis can be treated with carbarsone, tetracycline, or diiodohydroxyquin.

Geographic distribution

Worldwide. Pigs are a reservoir. Infection of people occurs more frequently in areas where pigs comingle with people, including the Philippines, Mexico, South America and Papua New Guinea.

Less than 1% of the human population is infected worldwide.

References

• CDC’s Division of Parasitic Diseases

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