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Balantidium coli is a species of ciliate protozoan, and is the only one that is a pathogen of humans. It is carried by pigs, rats, humans and guinea pigs. It can be transmitted between these species mostly via fecal transmission.
Cysts are the parasite stage responsible for transmission of balantidiasis. The host most often acquires the cyst through ingestion of contaminated food or water
Following ingestion, excystation occurs in the small intestine, and the trophozoites colonize the large intestine . The trophozoites reside in the lumen of the large intestine of humans and animals, where they replicate by binary fission, during which conjugation may occur . Trophozoites undergo encystation to produce infective cysts . Some trophozoites invade the wall of the colon and multiply. Some return to lumen and disintegrate. Mature cysts are passed with feces . Symptoms can be local due to involvement of the intestinal mucosa, or systemic in nature.
Geographic Distribution
Worldwide. Because pigs are an animal reservoir, human infections occur more frequently in areas where pigs are raised. Other potential animal reservoirs include rodents and nonhuman primates.
Source : http://www.dpd.cdc.gov/dpdx/HTML/Balantidiasis.htm
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