Case of the Week 288

The following were seen in a Giemsa-stained thin blood film from a child from Cameroon.

Identification?

Answer to Case 288

Answer:  Plasmodium ovale

Marco Ligozzi and Dr. Rajani nicely described the features of P. ovale:

"The parasitized erythrocytes are oval in shape and fimbriated at the end," "Schuffner's stippling is present, more evident especially at the edges of the erythrocyte"and malaria "pigment is scattered, coarse."

Of note, Dr. Rajani points out that Schuffner's dots are "relevant to P. ovale infection; yet, these dots also appear in cases of P. vivax infection."  Therefore it is incumbent upon us to look at other features that would allow us to differentiate P. ovale from P. vivax.  The features that I find most useful for differentiating the 2 species are:

• 1/3 or more of P. ovale infected erythrocytes are oval, while P. vivax infected cells are only rarely oval.
• The parasite forms of P. ovale are more compact than those of P. vivax (which are characteristically ameboid)
• Fimbriation is common with P. ovale.

Other minor features that are useful for differentiating the 2 species:

• Plasmodium ovale has coarser pigment than P. vivax.
• Mature schizonts of P. ovale have 6-14 merozoites while those of P. vivax have 12-24 (obviously this feature is only helpful when you see a schizont with >14 merozoites - indicating that the species is P. vivax; immature schizonts of both species can have less than 12 merozoites, so this is less helpful).

   Here is an image from this case, demonstrating some of these important features:

Case of the Week 287

Best wishes for the holidays from Creepy Dreadful Wonderful Parasites

Answer to Case 287

Answer:  Kissing Fleas!  (Ctenocephalides sp. - dog and cat flea) 

From Blaine Mathison who really outdid himself on this one:

Twas the night before Christmas when all through the house

the fleas were all nestled in the fur of the mouse.

They paired with their loved ones under a sprig of mistletoe,

A gift from Cousin Chigoe, from down south in the toe.

The larvae were pupating in the bed of the host,

carrying Dipylidium cysticercoids, an infectious dose!

The Yersinia pestis churned in the foregut

until such time when the proventriculus would erupt!

All of a sudden there appeared such a clatter!

The fleas sprang from the fur to see what was the matter.

Crawling up the leg of the host, with such stealth and so quick,

was the holiday icon known as St. Tick.

“Now Ixodes, now Dermacentor, and Amblyomma!

On Rhipicephalus, Ornithodoros, don’t forget Hyalomma.”

He got right to work and delivered the fleas' presents

full of pathogens to spread to medieval peasants,

Then he sprang to his sleigh and let out a whistle,

Then they took off into the night like a guided missile.

But I heard him exclaim as flew out of sight,

Merry Christmas to all, and to all a good bite!

Happy New Years Everyone!

Case of the Week 286

The following were found in the stool of a 20 year old woman.  She is otherwise asymptomatic.  The objects measure 2 to 3 mm in length.

Squashing one of the objects under a coverslip allowed for extrusion and visualization of the following structures (100x and 1000x magnification):

Identification?

Answer to Case 286

Answer:  Dipylidium caninum proglottids

Although this patient is much older than usual for D. caninum infection, the appearance of these proglottids is classic, with the small size and shape resembling "grains of rice."  We were also able to confirm our diagnosis by expressing immature eggs in packets out of the proglottids (1 egg packet shown by arrows below):

Case of the Week 285

This week's case was generously donated by Dr. Bryan Schmitt and Dr. Ryan Relich (Microbe Man).

An HIV positive man from the U.S. presented with multiple anal and rectal condylomas.  No travel history is available.  Excision with histopathology (H&E staining) showed the following:

(40x total magnification)


(500x total magnification)

(1000x total magnification)

GMS stain:

Answer to Case 285

Answer:  leishmaniasis, presenting as atypical perianal and rectal wart-like lesions (see below for patient follow up)

As Anon and Florida Fan mention, the differential of small intracellular objects in the 2-5 micron range includes leishmania amastigotes, small yeasts (primarily Histoplasma capsulatum), microsporidia spores, and Toxoplasma gondii tachyzoites.

We can exclude Histoplasma capsulatum, other yeasts, and microsporidia based on the negative GMS stain, thereby leaving Toxoplasma and Leishmania  in our differential.  These two organisms are differentiated by morphologic features: Toxoplasma gondii tachyzoites are arc-shaped with a small eccentric nucleus (see case 284), while Leishmania sp. amastigotes are oval and have an eccentric nucleus AND a rod-shaped kinetoplast.  Although it can be challenging to appreciate morphology in formalin-fixed, paraffin-embedded sections, this case actually allowed us to see some good examples of a kinetoplast (arrow) next to the nucleus (arrowhead):


Therefore, we can say that the patient most likely has leishmaniasis, although the unusual presentation of wart-like peri-anal and rectal lesions raises the question of whether this represents atypical cutaneous disease or visceral disease involving the GI tract and extending to the perianal skin.

To help solve this mystery, we needed additional information, and it turns out, an additional procedure needed to be performed.  The patient was from Nicaragua, where cutaneous, mucocutaneous, and visceral disease has been described.  He has been in the U.S. for approximately 6 years and hasn't traveled outside of the U.S. since.

To evaluate for visceral involvement, a bone marrow biopsy was then performed, which confirmed the presence of amastigotes.  Therefore, this case represents an unusual presentation of visceral leishmaniasis, masquerading as anal warts!

Material from the bone marrow biopsy has now been sent to the CDC for species determination.

Many thanks to Bryan Schmitt for the interesting case!

Case of the Week 284

The following are touch and smear-preparations of brain tissue from a HIV-positive male with necrotic cortical lesions.

Giemsa, 400x magnification

Giemsa, 1000x magnification

Identification?

Answer to Case 284

Answer:  Toxoplasma gondii tachyzoites
Note the arc-shaped tachyzoites, each with an eccentric nucleus, amid a background of host cell nuclei.

As pointed out by Anonymous, this used to be a pretty common scenario back in the early AIDS era. Fortunately CNS toxoplasmosis is now pretty rare in the HIV positive population due to the availability of good antiretroviral medications (in parts of the world, at least) and widespread use of prophylactic medications in susceptible medications.

I don't have the full history in this patient, but there was a question about the patient's compliance with prescribed medications.

Here's a poem from Blaine this week - a little on the dark side:

Old McDonald had a farm…E-I-E-I-O

And on his farm he had a cat…E-I-E-I-O

With a ‘meow meow’ here and a ‘meow meow’ there…

Poopin’ out oocysts everywhere.

Necrotic cortical lesions, oh the despair! E-I-E-I-O