Pathology and Mechanism of Disease in Kala-Azar

Abstract

Visceral leishmaniasis (VL) or kala-azar is a neglected tropical disease caused by the intracellular protozoan Leishmania donovani and is transmitted by an infected female sand fly vector. The sand fly inoculates the promastigote form of the parasite to the human host through the dermis during a blood meal. This extracellular form is rapidly taken up, principally by the host macrophage, where it undergoes metamorphosis to an amastigote . After rupture of the macrophage, the amastigote circulates in the blood and other body tissues. These amastigotes are again taken up by another sand fly during its next blood meal and again transform in the fly gut to its infective promastigote form to infect the next victim. After a variable incubation period there develops a spectrum of clinical manifestations like fever, weight loss, anaemia, and splenomegaly. These clinical manifestations are associated with immune suppression (CMI) leading to parasite survival accompanied by induction of IL-10 and/or IL-4 in tissues, hypergammaglobulinemia, and an increased amount of IL-4 in the blood of VL patients.