Answer to Case 721

 Answer to the Parasite Case of the Week 721: Cryptosporidium sp. oocysts. These oocysts are a parasite, even though they stain with the non-specific calcofluor white fluorescent dye. Also, the abbreviation "crypto" is often used to refer to either Cryptosporidium (parasite) or Cryptococcus (fungus), so it's always good to make sure you audience know what you were talking about!

Cryptosporidium spp. oocysts are one of several intestinal parasites that stain red with the modified acid fast stain; Cyclospora spp. and Cystoisospora belli are the other two. Note that these 3 parasite genera are commonly referred to as coccidian parasites (i.e., member of teh Coccidia group). However, evidence now indicates that Cryptosporidium more closely related to the Gregarinasina group. I've purposely shown these 3 organisms in my last 3 cases for comparison. Here is a composite image of the 3 parasites together:

Thanks again to Dr. Nazia Nagi for donating the C. belli case.