Table 8 provides a brief comparison of the size, shape, and other morphologic features of the "other" protistan parasites seen in the stool, the Microsporidia, the Sporozoa, and Blastocystis covered in this course.
Table 8. Summary of the Morphologic Features of
Blastocystis, Sporozoa, and Microsporidia.
| Organism | Size and Shape | Comments |
| Cryptosporidium spp. | Oocyst round; 4–6 μm | Oocyst is diagnostic in the stool; 4 sporozoites occ. seen in oocyst; acid-fast positive |
| Cyclospora cayetanensis | Oocyst round; 8–10 μm | Oocyst stained with acid-fast stain is variable in color; looks similar to Cryptosporidium, but twice as large |
| Cystoisospora belli | Ellipsoidal oocyst; 20–30 μm x 10–19 μm | A mature oocyst contains two sporocysts, each having 4 sporozoites; acid-fast positive |
| Sarcocystis spp. | Thin-walled oocyst contains 2 ovoid sporocysts, which each measure 10-16 μm x 7.5–12 μm | Ovoid sporocyst seen either together in oocyst or singly; fluorescence under UV light |
| Blastocystis hominis | Round organisms; 6–40 μm; can contain a large central body looking like a vacuole | Amoebic form is difficult to see; the central body form varies widely in size; and can be seen in wet mounts |
| Microsporidia | Spores usually round very small, 0.7–4 μm | Special stains such as chromotrope (modified trichrome) and chemofluorescent optical brightening agents work best |
