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Encompassing a complex group of disorders, leishmaniasis is caused by unicellular eukaryotic obligatory intracellular protozoa of the genus Leishmania and primarily affects the host’s reticuloendothelial system. Leishmania species produce widely varying clinical syndromes ranging from self-healing cutaneous ulcers to fatal visceral disease. These syndromes fall into three broad categories: visceral leishmaniasis (VL), cutaneous leishmaniasis (CL), and mucosal leishmaniasis (ML).
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ETIOLOGY AND LIFE CYCLE
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Leishmaniasis is caused by ~20 species of the genus Leishmania in the order Kinetoplastida and the family Trypanosomatidae (Table 221-1). Several clinically important species are of the subspecies Viannia. The organisms are transmitted by phlebotomine sandflies of the genus Phlebotomus in the “Old World” (Asia, Africa, and Europe) and the genus Lutzomyia in the “New World” (the Americas). Transmission may be anthroponotic (i.e., the vector transmits the infection from infected humans to healthy humans) or zoonotic (i.e., the vector transmits the infection from an animal reservoir to humans). Human-to-human transmission via shared infected needles has been documented in IV drug users in the Mediterranean region. In utero transmission to the fetus occurs rarely.
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