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[Cystoisospora belli (syn. Isospora belli)]

The oocysts of C. belli are large (25 to 30 µm) and  have a typical ellipsoidal shape.  When excreted, they are immature and contain one sporoblast.  The oocyst matures after excretion: the single sporoblast divides in two sporoblasts, which develop cyst walls, becoming sporocysts, which eventually contain four sporozoites each.  Cystoisospora will autofluoresce under ultraviolet (UV) microscopy.

A	B

A:  Immature oocyst of C. belli in an unstained wet mount showing a single sporoblast.
B:  Immature oocyst of C. belli in an unstained wet mount showing two sporoblasts.

C	D

C:  Same oocyst as in Image A but viewed under differential interference contrast (DIC).
D:  Same oocyst as in Image B but viewed under DIC.

E	F

E:  Same oocyst as in Images A and C but viewed under ultraviolet (UV) fluorescent micrscopy.
F:  Same oocyst as in Images B and D but viewed under UV microscopy.