Question 11: On Ziehl-Neelsen (ZN) staining oocysts of size 8-10 µm are visible. Identify the organism.
- A. Microsporidium
- B. Cryptosporidium
- C. Isospora belli
- D. Cyclospora (Correct Answer)
Explanation: ***Cyclospora***
- *Cyclospora cayetanensis* oocysts are **spherical** and measure **8-10 µm** in diameter, exactly matching the size described in the question.
- They are **partially acid-fast** on ZN staining and may show **internal structures** or appear **wrinkled**, making them visible under microscopic examination.
*Microsporidium*
- *Microsporidium* are extremely small (**1-4 µm**) **intracellular obligate parasites**, much smaller than the 8-10 µm oocysts described.
- They require **special staining methods** and are not typically visible with standard ZN staining due to their minute size.
*Cryptosporidium*
- *Cryptosporidium parvum* oocysts are **spherical** and measure **4-6 µm** in diameter, which is smaller than the 8-10 µm described.
- While they are **acid-fast** on ZN staining, their smaller size distinguishes them from the oocysts in question.
*Isospora belli*
- *Isospora belli* oocysts are **elongated or oval** and measure **20-30 µm** in length, making them significantly larger than the 8-10 µm oocysts described.
- Although they are **acid-fast** and visible on ZN staining, their larger size and oval morphology do not match the question parameters.