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[Cryptosporidium spp.]

Cryptosporidium spp. oocysts are rounded and measure 4.2 to 5.4 µm in diameter.  Sporozoites are sometimes visible inside the oocysts, indicating that sporulation has occurred.

A

A: Cryptosporidium spp. oocysts (pink arrows) in wet mount.  A budding yeast (brown arrow) is in the same field.

B

B:  Cryptosporidium parvum oocysts in wet mount, under differential interference contrast (DIC) microscopy.  The oocysts are rounded and measure 4.2 µm - 5.4 µm in diameter.  Sporozoites are visible inside the oocysts, indicating that sporulation has occurred.  (In comparison, oocysts of Cyclospora cayetanensis, another important coccidian parasite of humans, are twice larger and upon excretion are not sporulated, i.e., do not contain sporocysts.)