Light micrograph (LM) showing the internal protozoan parasite species Isospora belli, responsible for the condition isosporiasis. Immunocompromised patients are vulnerable to the disease, which is otherwise rare in humans; if it does appear, it is usually confined to the digestive tract. In this patient, who had AIDS, the parasite was disseminated throughout the body. Magnification 1500x at 35mm.