Leishmaniasis: A parasitic disease that is spread by the bite of sand flies infected with the protozoa Leishmania. There are several forms of leishmaniasis, the most common being cutaneous and visceral leishmaniasis (known as kala-azar). The cutaneous form of the disease causes skin sores and is usually named for a geographic place (for example, Jericho boil, Baghdad button, Delhi sore). Visceral leishmaniasis affects the internal organs of the body and can be fatal. See also kala-azar.