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Parasite Case of the Week 7

Welcome back to the Parasite Case of the Week!  I post a new case every Monday, along with the answer to the previous week’s case.  Here is our new case for this week:

The following is an hematoxylin and eosin stained skin biopsy taken from a mission worker who just returned from the Middle East. He presented with a 5 cm, non-healing ulcer. The biopsy shows numerous small (2-3 micron) objects inside macrophages. The arrows point to a defining feature of the organisms. Identification? Note that the organisms are scant, and hard to make out, even under 1000x oil immersion. What type of slide preparation is better for showing the morphology of this parasite? Based on these images, what is your differential diagnosis? And finally, what special stain would help you exclude some of the other possible diagnoses?

Based on the history and small size of the objects of interest, my guess would be Leishmania.

The amastigotes of Leishmania are small (2-4 um) and are characterized by delicate cytoplasm, nucleus, and kinetoplast (no cell wall). Histoplasma, Toxo, and T. cruzi are in the differential, based on my Henry’s reading. I wouldn’t expect T. cruzi in a skin lesion and both Histo and toxo lack a kinetoplast. I would do a PAS stain for fungus and/or silver stain could help to rule out other organisms. Culture on Novy-MacNeal-Nicolle medium would provide speciation.

Leishmania donovani? Unlikely if only skin is involved but amastigotes can be found crowded in macrophages of the skin. I would bet on L. major, L. tropica, or L. donovani in the skin. I would stain with a PAS or silver stain for the possibility of fungus like Histoplasma. I would also stain with a giemsa stain to better evaluate for Leishmania or Trypanosoma.

Identification: Leishmania; most likely L. tropica or L. major.

Better slide preparation for showing the morphology of this parasite: “Brown-Hopps modified tissue gram stain best accentuates the kinetoplast, and produces minimal background staining and maximum contrast. Giemsa stains are of no value in tissue sections,” according to the AFIP.

Differential diagnosis based on morphology: Histoplasma or Trypanosome

Special stains to help exclude some of the other possible diagnoses: Giemsa – also to better evaluate the AFIP’s position