[Last Modified: ]

September 2003
Answer to Case 116
This was a case of microsporidiosis.  The diagnostic morphologic features observed were:

• the presence of round to oval spores of microsporidia (black arrows, Figure A).  They will stain pinkish red when using the Chromotrope 2R staining technique.  Often, an equatorial belt-like stripe can be seen in the spores.
• spores within the size range of microsporidia.  Spores of Encephalitozoon spp. measure 1.0 to 1.5 by 2.5 to 3.0 micrometers, consistently appearing larger than Enterocytozoon bieneusi spores (0.8 to 1.4 micrometers).  E. bieneusi is the most commonly recognized species causing diarrhea in immunocompromised patients. 

A

The difference in size between the spores allows a tentative genus-level diagnosis, but definitive confirmation depends on laboratory testing using one or more of the techniques listed above.  Green arrows in Figure A indicate yeast cells present in the specimen, and not a causal agent of disease.

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