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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.  Staining of Cryptosporidium spp. oocysts can be variable.  In particular, infections that are resolving can be accompanied by increasing numbers of non-acid-fast oocysts “ghosts.”

A	B

A: Cryptosporidium sp. oocysts (red arrows) that did not take up the modified acid-fast stain.  The slide was counterstained with methylene blue.  Note that yeast cells did stain red (yellow arrows).
B: Unstained Cryptosporidium sp. oocysts (black arrows) on a slide stained with modified acid-fast.  The slide was counterstained with malachite green.