The coccidian parasite Cystoisospora belli (=Isospora belli) (phylum Apicomplexa) infects the epithelial cells of the small intestine of humans and causes diarrheal disease and a suite of symptoms known as cystoisosporiasis. It is the least common of the intestinal coccidia that infect humans. Cystoisospora belli occurs worldwide, especially in tropical and subtropical areas. Infection and more serious symptoms occur especially in immunodepressed individuals (e.g., AIDS patients) and outbreaks have been reported in institutionalized groups in the United States. (Source: Centers for Disease Control Parasites and Health Website) Contaminated food and water are generally believed to be the primary mode of transmission.
This parasite appears not to require a non-human host in its life cycle, completing both asexual and sexual phases within a single human host. However, it is not yet clear whether other animals may nevertheless function as reservoirs or paratenic hosts (i.e., hosts not required for the life cycle, but which may sustain it until it reaches an appropriate host). The oocysts of C. belli usually require less than one day to a few days after passage from a human intestine to complete sporogonic development and become infective. (Lindsay et al. 1997; Jongwutiwes et al. 2007) Lindsay et al. (1997) reviewed the life cycle of C. belli and related species (Lindsay et al. 1997). The biology of related parasites infecting domesticated mammals and non-human primates was reviewed by Lindsay and Blagburn (1994).