Balantidium coli cysts
is the largest intestinal protozoan of humans. Acquired by ingestion of cysts from the stool of an infected person, Balantidium causes recurrent diarrhea alternating with constipation. These pathogens move by means of cilia (short hair-like filaments) and thus are in the class Ciliata. Balantidium cysts possess two nuclei: a micronucleus and a distinctive kidney-shaped macronucleus. The outside of Balantidium trophozoites ("trophs") is covered with cilia for motion. In the cyst the cilia are inside the cell.
The cyst stage of Balantidium is circular in shape, whereas the troph is somewhat oval.
Diagnosis depends upon finding Balantidium cysts or trophs in the stool. The cysts are shown in these images.
Click on each image to see the enlarged version.
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| 1. cyst 400 X | 2. cyst 400 X | 3. cyst 400 X | 4. cyst 400 X | 5. cyst 400 X |
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| 6. cyst 1000 X | 7. cyst 1000 X | 8. cyst 1000 X | 9. cyst 1000 X | 10. cyst 1000 X |
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