"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

May 8, 2010

May 8 - Dientamoeba fragilis

Although Dientamoeba fragilis is an extremely common parasite, many details about its biology remain to be answered. Originally taxonomically grouped with amoebas, later ultrastructural studies followed by molecular work has instead showed that it is more closely related to Trichomonas than Entamoeba. The single-celled organisms are primarily found in the large intestines of people and other animals and can produce classic symptoms of traveler's diarrhea. The name of this species comes from the fact that it typically exists in a binucleated state (as in the photo - I think it looks like a Pacman ghost). The exact mechanism of transmission of D. fragilis is still not known. Cysts have never been observed - at least in humans, though a fecal-oral route is presumed. Some theorize that pinworms (Enterobius) or other helminths act as mechanical vectors for the D. fragilis, but this has not borne out in all cases.


  1. Did you mean "to Trichomonas than Entamoeba?"

  2. Reminds me of the good old days when Sherwin Desser had Henry Hong sifting through buckets of human feces for Enterobius so as to thoroughly test the transmission theory. The premise of that theory is of course based on Histomonas meleagridis being transmitted by through the eggs of Heterakis gallinarum.

  3. Yes, Mike, thanks for catching that.