Leishmania is a haemoflagellate like Trypanosoma. It occurs as amastigote form in the vertebrate host and premastigote form in the invertebrate host. This protozoan is a digenetic as its life-cycle is passed in two hosts. The primary host is man and the secondary host is the sand fly (Phlebotomus sp). There are three very closely similar species of Leishmania and also are pathogenic to man. These are :
1. Leishmania donovani. It lives in the reticulo-endothelial cells of the visceral organs specially the spleen and cause visceral leishmaniasis or kala-azar. It was discovered by Leishman and Donovan (1903).
2. Leishmania tropica. It harbours the blood and reticuloendothelial cells causing Orinetal Sore.
3. Leishmania brasiliensis. It occurs in cutaneous and mucocutaneous parts causing mucosal leishmaniasis or Espundia.
L. donovani occurs as amastieote form in man, measuring 2-4 µm in diameter. Under light microscope a nucleus is seen. A rod-shaped kinetoplast and sometimes a basal granule is visible. Under electron microscope it possesses a single mitochondrion with few cristae. The kinetoplast is composed of DNA and is situated within the mitochondrion.
In the secondary host i.e. the sand fly, Phlebotomus rgentipes it appears as promastigote or leptomonad form. Here the body is elongated and measures 14-20 µm in length and 1.5-3.5 µm in width.
A round nucleus is placed in the centre of the body. An oval kinetoplast lies transversely near the anterior end of body, ahead of which is a small basal granule from which a flagellum is given out.
The animal takes its nourishment in saprozoic manner. It absorbs glucose, fructose etc. from the blood of man and from the alimentary canal of sand fly.
The mode of respiration is aerobic. Oxygen is taken from the blood of host through general body surface by diffusion. Carbon dioxide is eleminated out by diffusion through general body surface.
Nitrogenous waste products are also eleminated by diffusion.
Selected Reading of:
A Text Book of Invertebrates
by H.S. Bhamrah, Kavita Juneja