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Table 7
Differential
Morphology of Protozoa Found in Stool Specimens of
Humans: Ciliates, Coccidia, and Blastocystis
| Species | Size | Shape | Motility | Number of Nuclei | Other Features |
| CILIATES | |||||
| Balantidium coli | |||||
| Trophozoite | 50-70 mm or more. Usual range, 40-50 mm. | Ovoid with tapering anterior end. | Rotary, boring. | 1 large, kidney shaped macronucleus. 1 small micronucleus immediately adjacent to macronucleus. Macronucleus occasionally visible in unstained preparations as hyaline mass. | Body surface covered by spiral, longitudinal rows of cilia. Contractile vacuoles are present. |
| Cyst | 45-65 mm. Usual range, 50-55 mm. | Spherical or oval. | 1 large macronucleus visible in unstained preparations as hyaline mass. | Macronucleus and contractile vacuole are visible in young cysts. In older cysts, internal structure appears granular. | |
| COCCIDIA | |||||
| Isospora belli | Oocyst: 25-30 mm. Usual range, 28-30 mm. | Ellipsoidal | Nonmotile | Usual diagnostic stage is immature oocyst with single granular mass (zygote) within. Mature oocyst contains 2 sporocysts with 4 sporozoites each. | |
| Sarcocystis | Sporocyst1 | Oval | Nonmotile | Mature oocysts with thin wall collapsed around 2 sporocysts or free fully mature sporocysts with 4 sporozoites inside are usually seen in feces. | |
| hominis | 13-17 mm. Usual range, 14-16 mm. | ||||
| suihominis | 11-15 mm. Usual range, 12-13 mm. |
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| Cryptosporidium | Oocyst: 3-6 mm. Usual range, 4-5 mm. |
Spherical or oval. | Nonmotile | Mature oocyst contains 4 "naked" sporozoites. No sporocysts are present. | |
| BLASTOCYSTIS | |||||
| Blastocystis hominis2 | |||||
| Vacuolated Form | 5-30 mm. Usual range, 8-10 mm. |
Spherical, oval, or ellipsoidal | Nonmotile | 1, usually, but 2-4 may be present. Located in "rim" of cytoplasm. In binucleated organisms, the 2 nuclei may be at opposite poles. In quadrinucleated forms, the 4 nuclei are evenly spaced around periphery of cell. | Cell contains large central body, or "vacuole" with a thin band, or "rim" of cytoplasm around the periphery. Occasionally a ring of granules may be seen in cytoplasm and the cell appears to have a "beaded rim". |
1 Sizes are based on information from
Rommel and Heydorn (1972) and Heydorn et al. (1975).
2 Description based on information from Zierdt,
1973 and McClure et al., (1980).
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