Coloured transmission electron micrograph (TEM) of Leishmania major cells grown in culture. Leishmania is a genus of parasitic protozoa that cause the disease leishmaniasis, a tropical disease transmitted by bites from infected sandflies. These cells are in the amastigote stage of their life cycle, which lacks flagella, and is the form Leishmania take within vertebrate hosts. Leishmania major is associated with the cutaneous form of leishmaniasis, which causes ulceration of the skin. This form is usually self-resolving, but may result in scarring.