(leishmaniasis)
Members of the genus Leishmania infect many vertebrates, including humans, dogs, and rodents. The life cycles of members of the genus involve a vertebrate host (e.g., the human) and a vector (a sand fly) that transmits the parasite between vertebrate hosts. In the vector the parasite takes on a characteristic morphological form known as the promastigote (see below), and it reproduces asexually in the vector's gut. When the vector bites the vertebrate host, promastigotes are injected into the vertebrate host. The promastigotes enter cells of the vertebrate host and change into a form called the amastigote (see below). The amastigote reproduces in the host's cells, and when the cell eventually dies the amastigotes are released and infect other cells (view a diagram of the life cycle). The symptoms and pathology associated with leishmaniasis result from the amastigotes killing the host's cells.



There are many different "diseases" caused by Leishmania. In some diseases the amastigotes do not spread beyond the site of the vector's bite. This results in a "cutaneous leishmaniasis" (oriental sore, Jericho boil, Aleppo boil, or Dehli boil) that often heals spontaneously (view geographic distribution). In other instances the amastigotes may spread to the visceral organs (liver, spleen), resulting in "visceral leishmaniasis" (kala-azar or Dum-Dum fever) (view geographic distribution) or to the mucous membranes of the mouth and nose, resulting in "mucocutaneous leishmaniasis" (espundia or uta). Left untreated, these latter diseases result in high rates of mortality. The various types of leishmaniasis are confined primarily, but not exclusively, to Central and South America, central Africa, and parts of southern and central Asia.

Promastigotes of Leishmania sp. from culture. This is the life cycle stage that grows in the vector and that is injected into the human host when the vector feeds. The promastigotes are approximately 25 µm in length.



Amastigotes (*) of Leishmania donovani in the cells of a spleen. The individual amastigotes measure approximately 1 µm in diameter. The amastigotes reproduce asexually in these cells.



Amastigotes of Leishmania in a macrophage from a lymph node of a dog. Original image from Oklahoma State University Parasitology Teaching Resources Web Site.)



A macrophage filled with Leishmania amastigotes.



A cutaneous leishmaniasis lesion on the arm.



Cutaneous leishmaniasis of the face. (Original image from and copyrighted by Dermatology Internet Service, Department of Dermatology, University of Erlangen.)