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Leishmaniasis is a protozoal disease caused by species of Leishmania.

A female sandfly acquires the amastigote- an intracellular non-motile form of the parasite- from another infected host, like a dog.

Inside the sandfly, the amastigote changes to promastigotes, a motile, flagellated form.

These sandflies then bite humans and inject the replicating promastigotes.

In cutaneous leishmaniasis, promastigotes are phagocytosed by skin-resident macrophages and enclosed within phagolysosomes.

Within phagolysosomes, they differentiate into amastigotes that tolerate acidic pH and replicate intracellularly. When infected macrophages rupture, the released amastigotes infect neighboring macrophages.

This infection typically produces localized cutaneous lesions that appear as small, asymptomatic papules.

Over time, these skin abnormalities can develop into well-circumscribed ulcers with a raised, violaceous border and epidermal breakdown.

In visceral leishmaniasis, the amastigotes spread through mononuclear cells in the bloodstream to the spleen, liver, bone marrow, and intestinal lymph nodes, causing systemic infection in the host.