New World cutaneous leishmaniasis arises from infection with parasites belonging to the L. mexicana group or the L. viannia group. In areas of Central and South America, infection with organisms of the L. mexicana group produces cutaneous leishmaniasis. A few autochthonous cases have been found in Texas. Infections with strains of L. viannia , which are endemic in various areas of South America, cause cutaneous leishmaniasis and may result in the later development of mucocutaneous leishmaniasis. All of these New World leishmanial parasites are transmitted principally by sandfly vectors, although direct human contact may also bring about infection.
Various mammals are naturally infected reservoirs of the organisms.
Clinical Features and Pathogenesis Both Old World and New World forms of leishmaniasis are initiated when the bite of an infected sandfly injects promastigotes into the human host. The organisms enter tissue macrophages and capillary endothelial cells, become amastigotes, and multiply. A granulomatous inflammatory response develops at the bite site. In Old World cutaneous leishmaniasis, after an incubation period of weeks to months, a papule develops at the inoculation site. This area may resolve spontaneously.