Answer to Case 224

Answers:

The viewers did a great job answering this case, and so I will just cut and paste from the comments:

Florida Fan said...

The blood case: only ring forms found, ring diameter smaller than half of infected red cell, infected cells not enlarged. A few ring have two nuclei, one applique form found. Based on these findings, the organism is consistent in morphology with P. falciparum.

(Notes from Parasite Gal - Babesia spp. would also be in the differential diagnosis, although the ring forms are fairly regular in size and shape and there are no extracellular forms or maltese crosses.  Therefore this appearance is more consistent with Plasmodium falciparum.  This also fits with the travel history.)

The second case: A ring of nuclei distributed on the edge of the cell (actually think of it as a clear spherical glass ball and some body just stick a few globs of play dough, if you rotate this ball, you will see different variations in morphology of the distribution of the play dough globs). The identification is therefore B. hominis.

(Notes from Parasite Gal - I like the "globs of Playdough" analogy!  Also, Hans points out that there is taxonomic confusion about Blastocystis, and that there are actually multiple sub-species/genotypes, or possibly multiple species, and therefore it is more correct to say "Blastocystis species" rather than "Blastocystis hominis").

Finally, although there was some debate on the size measurement, the consensus for the last image is Cryptosporidium species, based on the fact that the oocyt shown is less than 8-10 microns, and closer to 6.

Thank you for all of the great comments!