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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, B: Cryptosporidium parvum oocysts stained with modified acid-fast.  Against a blue-green background, the oocysts stand out in a bright red stain.  Sporozoites are visible inside the two oocysts to the right (Figure A).

C	D

C, D: Cryptosporidium sp. oocysts stained with modified acid-fast.