Answer to Case 411

Answer:  Malaria due to Plasmodium falciparum 

This case generated a lot of great discussion! As nicely described by Arthur V, there are "multiple infected RBCs containing 1 or more ring forms." Also, "the RBCs don't seem to be enlarged", "there are no amoeboid ring forms" and "the parasitaemia appears to be moderate judging by the number of ring forms present on the thick smear." These features, along with the absence of late-stage trophozoites and other intermediate forms are all consistent with P. falciparum infection. The following annotated images demonstrate some of the characteristic features seen in this case:

Thanks to everyone who wrote in on this interesting case.