Sunday, September 17, 2017

Answer to Case 460

Answer: Neobalantidium (formerly Balantidium) coli trophozoite

The identification can be made by recognizing the characteristic morphologic features and motility of the N. coli trophozoite. In this case, you can appreciate the circumferential cilia, large size (40 to 200 microns in greatest dimension) and macronucleus (partially seen in this case). The multiple globular structures within the trophozoite likely represent ingested microorganisms and cytoplasmic vacuoles.
The motility of N. coli is commonly described as 'boring', but as Mark Fox mentioned, this term is a bit misleading since there is nothing uninteresting about it! The alternative term, 'rotary', is perhaps a bit more illuminating.

Of note, several readers mentioned that N. coli is associated with pigs and therefore inquired if patient had any pig exposure. Unfortunately we don't have that information in this case. However, this raises the additional point that the patient was also infected with Ascaris and pigs can be also infected with this round worm. Therefore, the case for potential pig exposure is very intriguing!

For those of you that like (or care about) taxonomy, I should mention that Ascaris suum (the species attributed to pigs) is now thought to be the same species as the human parasite, A. lumbricoides. This assertion is based on the numerous morphologic and genetic similarities that have been described between the two (see "Are Ascaris lumbricoides and Ascaris suum a single species?" by Leles et al. HERE). If they are the same species, then the name A. lumbricoides takes precedence since it was described first (1758 vs. 1782). Isn't taxonomy fun?

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