A parasitic disease caused by different species of the genus <i>Leishmania</i>, transmitted through the bite of hematophagous female phlebotomine sand flies. The clinical spectrum ranges from asymptomatic to clinically overt disease which can remain localized to the skin or disseminate to the upper oral and respiratory mucous membranes or throughout the reticulo-endothelial system. Three main clinical syndromes have been described: visceral (or Kala-Azar; with fever, weight loss, hepatosplenomegaly), cutaneous, and mucocutaneous leishmaniasis (cutaneous or mucocutaneous ulceration).

Presence of a protracted or persistent infection by a pathogen potentially related to an underlying abnormality of the immune system that is not able to clear the infection.