Answer to Parasite Case of the Week 543: Cryptosporidium sp. oocysts
The case shows how Cryptosporidium oocysts look in a variety of different preparations including phase contrast (very cool). As we are all taught during training, Cryptosporidium spp. oocysts are red-pink using a modified acid fast stain (as shown in image 3 of this case) and measure 4-6 micrometers in diameter, thus allowing their differentiation from the similarly-appearing Cyclospora cayetanensis oocysts (which are 8-10 micrometers in diameter). Florida Fan reminded us that not all of the oocysts will reliably stain with the modified acid fast stain, and thus some may appear as 'ghost' cells or negative outlines. A modified safranin stain can also be used and has been reported to more reliably stain the oocysts.
Florida Fan mentioned that the direct fluorescent antibody (DFA) for Cryptosporidium spp. oocysts - widely regarded as the most specific microscopic method - doesn't necessarily detect all Cryptosporidium species, and thus there is the potential false negative results. In certain cases, confirmation with another method may be helpful.
Finally, Old One tells a tale of prior infection in our case comments that he thankfully survived! It is indeed possible that his prior infection stimulated development of a protective immune response - likely an interferon-gamma mediated memory T cell response. However, it is not clear if this immune response would prevent future infections with all different species of Cryptosporidium.
Thanks again to Idzi for sharing this beautiful and classic case!
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1 comment:
You're making me feel ancient. Back when I was in the saddle we primarily diagnosed Crypto with ZnSO4 centrifugal flotation. Later we would verify with an acid fast stain, then finally we updated to the IFA test. During that "Epoch" we were happy just to ID to genus. Live and learn
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