Leishmaniasis is one of the most important vector-borne diseases of humans. This parasitic disease can be caused by many species of Leishmania, most of which are zoonotic. In humans, different species of the parasite are associated with different forms of the disease. Many Leishmania spp. cause skin ulcers and nodules. A few of these organisms can also affect the mucous membranes, and may cause disfiguring lesions of the nose. Other species damage the internal organs and cause human visceral leishmaniasis, a life-threatening condition. Among domesticated animals, dogs are the most important species in the epidemiology of this disease. In addition to becoming ill, dogs are reservoir hosts for L. infantum, one of the two most important organisms in human visceral leishmaniasis. Skin lesions and, rarely, visceral disease, have also been reported occasionally in other domesticated animals, captive mammals in zoos, and wild animals.