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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 sp. oocysts stained with trichrome.  Oocysts may be detected, but should not be confirmed by this method.  Trichrome staining is inadequate for a definite diagnosis because oocysts will appear unstained.  Here the Cryptosporidium oocysts are represented by red arrows; the blue arrows represent yeast.