Isospora belli is a single-celled parasite that belongs to the group of organisms known as coccidia. It primarily infects the intestines of humans, leading to a condition called isosporiasis. This parasite is transmitted through the ingestion of oocysts, which are found in contaminated food or water. Infections with Isospora belli can cause symptoms such as diarrhea, abdominal pain, and weight loss. While healthy individuals may recover without treatment, those with weakened immune systems, such as individuals with HIV/AIDS, are at a higher risk for severe illness. Diagnosis is typically made through stool examination to identify the oocysts.