Cycle in Man
When an infected sand fly sucks the blood of man along with its saliva a number of promastigote forms enter the blood stream of man. Here they become amastigote forms by losing their flagella. It attacks the macrophage cell of liver or spleen. It appears to be well adapted to a life inside these cells. They remain unaffected by the proteolytic enzymes of host within the macrophage the Leishmania divides by binary fission once in every 24 hours. These are liberated in blood after the rupture of macrophage.
Cycle in Sand Fly
When the female sand fly sucks the blood of man along with blood and macrophages the Leishmania enter the alimentry canal. Within the gut they multiply by binary fission. Their number is increased during 4-5 days of blood meal. Soon the parasites migrate forward and the foregut is occupied by them. It gradually moves into the salivary glands by 7-8 days. The development is confined to fore-gut only.
Leishmania donovani causes visceral leishmainasis or Kala-azar of man throughout the warmer parts of Asia, South America, N. and E. Africa and the Mediterranean coast. In some areas, like China. Central Asia and S. America, the dogs are often infected and serve as reservoirs of the parasites.
In man the kala-azar starts as a primary leison in the skin. Alter 4-6 months the parasites spread to the viscera with a preference for liver, spleen and bone-marrow infecting the reticulo-endothelial system. Anaemia results from the invasion of bone marrow. Leishmaneasis is slow disease and is usually fatal if not treated It is some times followed by a nodular eruption of the skin which may be allergic in origin (post kala-azar dermal leishmoid), parasites are found in nodules. Treatment with compounds of antimony is often, but not always, effective.