Causal Agent:

The causal agent has been only recently identified as a single-celled coccidian parasite. The species designation Cyclospora cayetanensis was given in 1994 to Peruvian isolates of human-associated Cyclospora. It appears that all human cases are caused by this species.

Life Cycle:

Some of elements of this figure were created based on an illustration by Ortega et al. Cyclospora cayetanensis. In: Advances in Parasitology: opportunistic protozoa in humans. San Diego: Academic Press; 1998. p. 399-418.

When freshly passed in stools, the oocyst is not infective (thus, direct fecal-oral transmission cannot occur; this differentiates Cyclospora from another important coccidian parasite, Cryptosporidium). In the environment , sporulation occurs after days or weeks at temperatures between 22°C to 32°C, resulting in division of the sporont into two sporocysts, each containing two elongate sporozoites . Fresh produce and water can serve as vehicles for transmission and the sporulated oocysts are ingested (in contaminated food or water) . The oocysts excyst in the gastrointestinal tract, freeing the sporozoites which invade the epithelial cells of the small intestine . Inside the cells they undergo asexual multiplication and sexual development to mature into oocysts, which will be shed in stools . The potential mechanisms of contamination of food and water are still under investigation.

Life cycle image and information courtesy of DPDx.