Cystoisospora belli causes intestinal disease in several mammalian hosts, with infections believed to arise from the ingestion of sporulated oocysts in contaminated food or water. Infection, which is difficult to distinguish from cryptosporidiosis, is usually self-limiting and characterized by watery diarrhea, abdominal cramps, anorexia, and weight loss. Cystoisospora belli is often the agent responsible for traveler's diarrhea in travelers to developing countries where it is widespread. It is more common in AIDS patients, other immunocompromised patients, and indigenous populations in the United States.

(Fletcher et al. 2012 and references therein)