Describe the structure and life history of Leishmania donovani.

 Describe the structure and life history of Leishmania donovani.

Ans Classification in Outline :

Phylum : Protozoa

Sub-phylum : Sarcomastigophora

Super-class : Mastigophora.

Class: Zoomastigophora.

Order : Kinetoplastida,

Genus : Leishmania.

Species: Donovani.

It resides in the viscera and is the causative agent of visceral leishmaniasis

or fatal kala-azar. It is prevalent in eastern India, China, Central Asia, East

Africa, South America and Russia. Man becomes infected by becoming

associated with a sylvatic or non-domestic reservoir dog. Spreading of the

disease among being is caused by the intermediate host phlebotomus (Indian

vector)

Structure : Leishmanias are oval in shape and measure 2-4 micra by

1.5-2 micra. The nucleus is elongated with rodshaped kinctoplast which is

perpendicular to the nucleus. Flagellum is absent. Binary fission is the mode

of multiplication.

Life History : Members of the genus Leishmania which are parasitic

to man and other vertebrates occur in Leish-manial forms (flagellaless forms)

and in the intermediate hosts they seen in leptomonad forms (fiagellated

forms). Three members of the genus are parasites in man they offer close

resemblance to each other.

In man the leishmanias are

intracellular parasites of the reticulo endo-

thelial system namely, the endothelial

cells, large mononuclear leucocytes and

kuffer cells of liver. In case, of heavy

infection they have been found to invade

ectodermal cells and polynuclear

leucocytes. By their successive divisions

the parasites, become over crowded in the

host cell, which is ultimately destroyed.

The intermediate host is the sand fly belonging to the genus phelobotomus.

The fly ingests leishmanias along with the blood of the vertebrate host. In the

midgut of the fly the parasites increase in size, develop flagella and are

metamorphosed into long slender Leptomonad forms in four days. The

leptomonas multiply vigorously by binary fission and reach the proventriculus

of the fly. Repeated multiplication inside the proventriculus causes complete

obstruction of the organ. As a result, when the sand fly ingest blood, the meal

goes no further than the ocsophagus. This causes resurgitation of the sucked

blood and the leptomonads are introduced in the blood stream along with the

resurgitation