Case #183 - July, 2006

This was a case of cryptosporidiosis caused by Cryptosporidium sp. Although many laboratories may only perform wet mounts and trichrome staining for an O & P, confirmatory identification of Cryptosporidium must include examination of acid-fast smears and/or DFA. In wet mounts, Cryptosporidium sp. oocysts can easily be confused with yeast cells and often numbers can be quite low making detection a challenge. Diagnostic features observed in the acid-fast stained smears were:

• the size of the oocysts (4-5 micrometers in diameter), which was consistent with oocysts of Cryptosporidium spp. that can infect humans.
• oocysts that stain positive with acid-fast stain, although Cryptosporidium oocysts may stain variably.
• the presence of sporozoites (Figure A, arrow) within one of the oocysts. This characteristic is often easier to see on an acid-fast stained slide. Also in stained preparations dark granules of residual material may be present within some of the oocysts.

Figure A

Molecular tools are available to identify Cryptosporidium sp. at species level. Some of the species that infect humans cannot be distinguished morphologically.

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