Isospora belli

• 1. Name: Greek: isos = similar, identical; sporos = spore; kystos = cyst: Latin: bellum = belly.

• 2. Geographic Distribution/Epidemiology: Worldwide occurrence; several 100 millions infected people, not occurring as true epidemics.

• 3. Morphology/Life Cycle: This organism belongs to the so-called Coccidia, which are members of the former phylum Sporozoa/Apicomplexa in the newly created Alveolata. It parasitizes intracellularly the epithelial cells of the intestine of humans being situated inside a parasitophorous vacuole. Infection of humans occurs by oral uptake of oocysts of the Isospora type from remnants of human feces. The oocysts, which appear ovoid with a flattened pole (Figs. 1 and 3), are excreted non-sporulated. Outside of the host’s body, two sporocysts are developed within 2–3 days inside the oocyst finally containing each four sporozoites, which are the infectious stages after oral uptake of the oocyst by another human being (Figs. 2 and 3). These oocysts measure 25–35 ×...