Centers for Disease Control/Division of Parasitic Diseases and Malaria
EOL staff
Life cycle of Balantidium coli, the cause of human balantidiasis The cyst stage (1) of the B. coli life cycle is responsible for transmission.The host most often acquires the cyst through ingestion of contaminated food or water (2). Following ingestion, excystation occurs in the small intestine and the trophozoites colonize the large intestine (3). The trophozoites reside in the lumen of the large intestine of humans and other animals, where they reproduce by binary fission, during which conjugation may occur (4). Trophozoites undergo encystation to produce infective cysts (5). Some trophozoites invade the wall of the colon and multiply. Some return to the lumen and disintegrate. Mature cysts are passed with feces (1).From Centers for Disease Control Parasites and Health website
Centers for Disease Control/Division of Parasitic Diseases and Malaria
EOL staff
Life cycle of Cyclospora cayetanensis When freshly passed in stools, the oocysts of Cyclospora cayetanensis are not infective (1), so direct fecal-oral transmission cannot occur (this is in contrast to what is seen with another important coccidian parasite, Cryptosporidium). In the environment (2), sporulation occurs after days or weeks at temperatures between 22 C and 32 C, resulting in the division of the sporont into two sporocysts, each containing two elongate sporozoites (3). Fresh produce and water can serve as vehicles for transmission (4) and the sporulated oocysts are ingested (in contaminated food or water) (5). The oocysts excyst in the gastrointestinal tract, freeing the sporozoites, which invade the epithelial cells of the small intestine (6). Inside the cells, they undergo asexual multiplication and sexual development to mature into oocysts, which will be shed in stools (7). Potential mechanisms of contamination of food and water are still under investigation.From Centers for Disease Control Parasites and Health website.
