Protozoan Cystoisospora belli is a human parasite causing an intestinal disease known as cystoisosporiasis. Infection occurs via the fecal-oral or digestive tract. A direct human-to-human transmission of the parasite is unlikely. The disease has a mild, self-limiting course in immune competent individuals. People with immunodeficiency are more severely affected and may experience extreme diarrhea that may lead to weakness, anorexia, and weight loss. Other symptoms of cystoisosporiasis include abdominal pain, cramps, loss of appetite, nausea, vomiting, and fever. The distribution of this coccidian parasite is cosmopolitan, but it is mainly found in tropical and subtropical areas of the world such as the Caribbean, Central and South America, India, Africa, and South-East Asia. In the U.S. Cystoisospora belli infections are usually associated with HIV infections.