Isospora belli undergoes a classical coccidian cycle with schizogony and gametogony mainly in the small intestinal epithelium. Unsporulated oocysts 20–32 μm in size and containing 2 sporoblasts are shed in the stools. In addition, individual encysted zoites are found in the lamina propria and mesenteric lymph nodes (Pathology, Fig. 5c). These are similar to those that occur in cats and in rodents, which can serve as the intermediate hosts of feline Isospora, which has been reclassified as Cystoisospora felis and Cystoisospora rivolta. The presence of unizoic cysts suggests that the human I. belli may also be heteroxenous, and may better be classified as C. belli. There is an intense inflammatory reaction in the lamina propria involving plasma cells, lymphocytes, neutrophils, and eosinophilic granulocytes. With chronic infection there is villar atrophy. Intermittent diarrhea, malabsorption, and sometimes fever.