This cool large ciliate is one of my favorite parasites. It's the largest protozoan parasite and only pathogenic ciliate to infect humans. As my predecessor, Dr. John H. Thompson, used to say, it is the aircraft carrier of the fecal flotilla.
Diagnosis is made based on the characteristic morphologic features. As Florida Fan mentioned, "At first look, the spherical object on the left of the first picture and the one of the third picture may lure us to identify them as eggs of some sort," (indeed, B. coli cysts may be easily mistaken for helminth eggs), "but the oval large object on the right side of the first picture as well as the second photo when enlarged will show us the cilia. The second picture shows also a cytostome (oral groove) on the upper end of the object."
Here is a closer look at these morphologic features of the trophozoite:
So what's up with the taxonomy? Well Blaine Mathison and I just published an update on parasite taxonomy discussing the new name, Neobalantidium, so imagine my dismay when I realized that the older (and potentially valid name) of Balantidioides had already been described. As Blaine mentioned in his comment "It looks like when Neobalantidium was described in 2013, the authors overlooked a paper from 1931 that proposed the name Balantidioides. If it was simply an oversight on their part, then yes the name could indeed be Balantidioides. However, it is possible there was something in the description of Balantidioides that rendered the name invalid (i.e., rules of nomenclature where not followed, at least for what was acceptable at the time). There is also another nomenclatural rule that states if a name is not used in the literature for a specific amount of time, it can be rendered invalid (not sure yet it that applies here)." Perhaps some of my readers can provide more insight. We are also checking with our colleagues to get more information and will report back to you, dear readers, when we have more answers.
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