January 2022 – Infectious Disease Pathology

Leishmania spp.

The biopsy shows dermal chronic inflammation, and intracellular organisms that are 2-5 µm in size, with identifiable nuclei and small, dash-shaped kinetoplasts. These intracellular organisms are consistent with amastigotes. In this case, the clinical history and the morphology are consistent with Leishmania spp. causing cutaneous leishmaniasis. Non-healing skin ulcers in a patient with recent travel to South America should prompt clinicians and diagnosticians to consider this entity. Definitive species identification is achieved by molecular methods in reference laboratories, and is important for treatment, prognosis, and for documenting epidemiological case exposures.

Although Trypanosoma cruzi amastigotes are morphologically indistinguishable from Leishmania, Chagas disease is not compatible with the described clinical presentation; it usually affects cardiac and smooth muscle of the heart and gastrointestinal tract. A chagoma, the skin manifestation of the bite of the triatomine bug, is described as a swelling that can be erythematous or indurated, different from the lesions in our case.

Toxoplasma gondii tachyzoites, the actively dividing form of the parasite, are 4-8 µm elongated structures; this parasite can also be seen as bradyzoites forming tissue cysts, characteristically in the brain.

Histoplasma spp. and other yeasts lack kinetoplasts, but can overlap in size and potentially cause skin lesions.

References

1. Burza S, Croft, SL, Boelaert M. Leishmaniasis. The Lancet. 2018;392(10151), 951–970.