Monday, July 15, 2019

Case of the Week 552

This week's case is from Blaine Mathison. The following were seen on a trichrome-stained stool specimen. They averaged 5 to 7 micrometers in greatest dimension. A Giardia antigen test was positive.




Identification?

17 comments:

Idzi P. said...

Giardia Ag might be positive, but this looks like Chilomastix!
;-)

Lyne Cédilotte said...

Chilomastix mesnili trophozoites

Tracie Rose said...

I agree with Chilomastix. Does it cross react or is there Giardia hiding out in there too?

Hamdi said...

I butshilli

WarriorKim said...

From the nucleus and large vacuole, I'd say Iodamoeba.

Sam said...

I was going to say Enteromonas hominis...but then I read the other comments 🙁

Anonymous said...

Well, at first look I tend to agree with everyone on an identification of Chilomastix mesnilii. On second thought, the identification as Pentatrichomonas hominis would also be tempting.
Knowing Blaine's "modus operandum", I say to myself hey do not rush it. The ones above are from 6-12um, too big for the 5-7um given.
Finally, there is that little Rhetortamonas hominis with 4-10um size seems to be a likely candidate. As far as the Giardia antigen being positive, this is plausible since Giardia either cysts or trophs may and may not always be found in a genuine giardiasis.
Well, "no guts no glory". As I have been known to be wrong before Rhetortamonas will be my bet, please do not let me fool you.
Florida Fan

Debra V said...

I favour Trichomonas hominis but have never used Trichrome, so would like to see Iron-Harmatoxylin.

Bob said...

Florida Guy gives an interesting perspective. I was all for Chilomastix before his argument. Now I’m uncertain.

Anonymous said...

The morphology very much like Trichomonas, I think it is Trichomonas hominis
Is there any cross reaction with Giardia or the Giardia was too few.
I will stain with giemsa

Hans Naus said...

Chilomastix mesnilii tropho's

Sir Galahad said...


Chilomastix mesnili ( trophozoites)and Jodamoeba butschlii (trophozoites )

Anonymous said...

Dientamoeba fragilis, maybe?
I really don't know.
In my country we don't use stool stains, so I'll wait for the answer.

-HLCM fan.

Old One said...

Like HLCM fan, I seldom use stains so this is a bit out of line for me. I believe the unknowns are Chilomastix. Although it wound be gratifying if Florida Fan was correct.

Rosoff et. al.1989 reports that a certain percentage of samples tested were negative for Giardia by microscopic exam but positive for Giardia ang. Perhaps this is what happened in this case.

Anonymous said...

To Blaine,
For sure your cases are always challenging, yet if there was no challenge what will we learn? My experience both as a student and an instructor has shown that we learn more being challenged, and a challenging teacher always produce better students.
As such, thank you for your brain teasers.
To Old One,
We use both microscopy and Giardia Antigen EIA in our lab. Yes, the EIA is far more sensitive than the classic microscopy however, we cannot use one methodology to default the other one. For sure a positive microscopy is self evident that the patient is infected with Giardia, but a positive antigen EIA will persist after the patient has been successfully treated. Dr. Pritt can give us better elaboration on the clinical use of both test.
Florida Fan

ParasiteGal said...

As always, Florida Fan is correct in that the Giardia antigen can remain positive after successful treatment, in the absence of morphologically-identifiable organisms. I'm not aware of any literature on how long the antigen may be detectable, but most recommendations are not to re-test the patient until 2-4 weeks after treatment. Thank you all for your great comments!

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