Entamoeba dispar (Nonpathogen)

Organism:
This organism belongs to the amebae, is a nonpathogen, and causes no disease.  Both the trophozoite (usual size, 12-30 µm) and cyst forms (usual size, 10-20 µm) can be found in clinical specimens.

 

    Entamoeba histolytica                                
Note:  ingested RBCs in troph

       

Entamoeba histolytica/E. dispar

 

Life Cycle:
Large bowel, organisms passed in feces

Acquired:
Fecal-oral transmission via cyst form; contaminated food and water

Epidemiology:
Worldwide, primarily human-to-human transmission

Clinical Features:
None

Clinical Specimen:
Intestinal:  Stool

Laboratory Diagnosis:
Intestinal:  Ova and Parasite examination (concentration, permanent stained smear); fecal immunoassay for the Entamoeba histolytica/E. dispar group or the true pathogen, E. histolytica.

Organism Description:
Trophozoite:  Evenly arranged nuclear chromatin, central karyosome, fine cytoplasm (will normally not contain ingested RBCs)
Cyst:  May contain chromatoidal bars with smooth, rounded edges; mature cyst contains 4 nuclei (rarely more seen).

Laboratory Report:
Without confirmation using the specific immunoassay to detect the true pathogen, E. histolytica, the report must indicate:  Entamoeba histolytica/E. dispar group (indicate cysts and/or trophozoites); make sure your clients know what this report means in terms of pathogens/nonpathogens.

Report Comment:  Submit a fresh stool if you want confirmation of the true pathogen (Entamoeba histolytica).  The laboratory will then test the fresh stool (fresh, frozen, some acceptable in Cary-Blair) for the presence of the true pathogen, Entamoeba histolytica, antigen.  If confirmation of E. histolytica is not performed, then the physician will usually treat if the patient is symptomatic.

Treatment:
None, if it has determined via specific testing that the organism is truly the nonpathogen, E. dispar.

Control:
Improved hygiene, adequate disposal of fecal waste, adequate washing of contaminated fruits and vegetables

Comments:
E. histolytica (true pathogen, cause of amebiasis) cannot be differentiated from the nonpathogen, E. dispar (although when trophozoites are found to contain ingested RBCs, it is more likely to be E. histolytica and will be reported as such).  E. dispar does not normally ingest RBCs.