Diagnostic Findings [Last Modified: ]
Isosporiasis
[Isospora belli]
Causal Agent Life Cycle Geographic Distribution Clinical Features Laboratory Diagnosis Treatment

Microscopy

Isospora belli oocyst Isospora belli oocyst Isospora belli oocyst
A B C

A, B, C: Oocysts of Isospora belli.  The oocysts are large (25 to 30 µm) and have a typical ellipsoidal shape.  When excreted, they are immature and contain one sporoblast (A, B).  The oocyst matures after excretion: the single sporoblast divides in two sporoblasts (C), which develop cyst walls, becoming sporocysts, which eventually contain four sporozoites each.  Images contributed by Georgia Division of Public Health.

Comparison of coccidian parasites
Figure 2

Oocysts of Isospora belli can also be stained with acid-fast stains, and can be visualized by epifluorescence on wet mounts, as illustrated in Figure 2.  Three coccidian parasites that most commonly infect humans, seen in acid-fast stained smears (2A, 2C, 2F), bright-field differential interference contrast (2B, 2D, 2G) and epifluorescence (2E, 2H, C. parvum oocysts do not autofluoresce).
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