Which cyst has a nucleus with a prominent karyosome, a clear halo, no achromatic granules, and no peripheral chromatin?

Which cyst has a nucleus with a prominent karyosome, a clear halo, no achromatic granules, and no peripheral chromatin?

• A. Entamoeba histolytica
• B. Entamoeba nana
• C. Giardia lamblia
• D. Cryptosporidium parvum

Answer: (B)

Focus on how the cyst nucleus is organized. The described cyst shows a single nucleus with a prominent karyosome, a clear halo around it, and no peripheral chromatin or achromatic granules. That combination is characteristic of Entamoeba nana. The halo and the large, central karyosome with absence of a peripheral chromatin ring distinguish it from other intestinal amoebae. For example, Entamoeba histolytica cysts typically have up to four nuclei with a thin ring of peripheral chromatin around each nucleus, Giardia lamblia cysts contain two to four nuclei with distinctive chromatoid bodies and lack the halo pattern around the nucleus, and Cryptosporidium parvum oocysts are much smaller and do not show this nuclear morphology.

Focus on how the cyst nucleus is organized. The described cyst shows a single nucleus with a prominent karyosome, a clear halo around it, and no peripheral chromatin or achromatic granules. That combination is characteristic of Entamoeba nana. The halo and the large, central karyosome with absence of a peripheral chromatin ring distinguish it from other intestinal amoebae. For example, Entamoeba histolytica cysts typically have up to four nuclei with a thin ring of peripheral chromatin around each nucleus, Giardia lamblia cysts contain two to four nuclei with distinctive chromatoid bodies and lack the halo pattern around the nucleus, and Cryptosporidium parvum oocysts are much smaller and do not show this nuclear morphology.