Sunday, February 2, 2020

Answer to Case 579

Answer to Parasite Case of the Week 579: Entamoeba histolytica

This great case by Idzi nicely shows the directional motility of an E. histolytica trophozoite - something that is less commonly seen in the clinical laboratory as more fecal specimens are received in a fixative. This case also highlights the characteristic ingestion of red blood cells (erythrophagocytosis) by the trophozoites.

Dr. Graham Clark reminds us that non-pathogenic Entamoeba species may also ingest red blood cells that are in the environment, so correlation with clinical presentation, biopsy, antigen and/or PCR tests is also warranted.


Steven VDB, ITM said...

Thanks for this interresting case. It is mentioned that non-pathogenic Entamoeba species can also digest red blood cells. I thought that RBC's moving withing the amoeba is pathognomonic feature of E. histolytica. So I'm happy to learn which other Entamoeba species can also do this. Thanks in advance for your answer,
Steven Van Den Broucke
Lecturer ITM, Antwerp, Belgium

ParasiteGal said...

Hi Steven,
Yes, there are studies that show that E. dispar will also ingest RBCs from the environment - but at a lower rate than E. histolytica. I believe that the other non-pathogenic Entamoeba species can also do this. The U.S. CDC now has the following on their website to reflect this: "While the discussed species are morphologically-identical, E. histolytica may be observed with ingested red blood cells (erythrophagocytosis); E. dispar may occasionally be seen with ingested erythrocytes as well, although its capacity for erythrophagocytosis is much less than that of E. histolytica." Here is one study that I found from just a quick internet search:

We can ask Dr. Graham Clark from LSHTM for more information if you are interested.