fragilis is probably a non-pathogenic amoebae found in the gut of
about 25% of humans. Its presence has been associated with mild
abdominal complains such as diarrhoea, but it is not clear if the amoeba
is cause or effect of the upsets. It is between 4-18um and is the only amoeba in the human gut that has two nuclei
(this is why its called Dientamoeba), although many cells are mono-nucleate. It has been suggested that Dientamoeba may
have a flagellate stage (Jahn & Jahn, 1949). Dientamoeba fragilis
branches with the Trichomonads in a SSUrDNA analysis (Sogin
et al, 1996). Dientamoeba fragilis
does not have a cyst stage and so how the amoeba infects a quarter of the
population is something of a mystery, however it has been suggested that
the amoeba is carried into the human body within the eggs of the
pathogenic nematode Enterobius
vermicularis. Fortunately this
nematode is easily eradicated with metronidazole an inhibitor
of microtubules from some species.
Jahn, T.L. & Jahn, F.L. (1949). "How to know the Protozoa".
Iowa, Wm.C.Brown Publ.
Sogin, M. L., Silberman, J.D, Hinkle, G. & Morrison, H.G.
(1996). "Problems with molecular diversity in the eukarya.".Society of General
Microbiology Symposium: Evolution of microbial Life ed.Roberts, D.M., Sharp, P., Alderson,
G. & Collins, M.A. Cambridge University Press. pp167-184.