Sunday, March 29, 2015

Answer to Case 343

Answer:  Cyclosporiasis due to Cyclospora cayetanensis

Note the presence of both asexual and sexual forms within enterocytes:

As many readers noted, the differential diagnosis includes Cryptosporidium sp., Cystoisospora belli, and the microsporidia - all which can also be found within enterocytes.  They can be differentiated from Cyclospora cayetanensi by their size and location within the cell.

Cryptosporidium spp. undergo a complicated replication cycle outside of the enterocyte cytoplasm, just below the cell membrane (thus they are intra-cellular, extra-cytoplasmic).  They therefore appear as small 'blobs' on the surface of the intestine (arrow heads below):

Cystoisospora belli is more like Cyclospora cayetanensis in that the parasites replicate within the cytoplasm of the enterocytes. They are significantly larger than Cyclospora, which in my mind, is the main differentiating feature (images from the CDC DPDx):

Finally there are the microsporidia (usually Enterocytozoon bieneusi and Encephalitozoon intestinalis), which appear as very small intra-cytoplasmic objects.  You can see a nice Giemsa-stained image from Para-site online.

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