Kala-azar is caused by
Leishmania donovani
Leishmania donovani is an intracellular parasite in leucocytes or cells of liver, spleen, bone marrow, lymphatic glands, etc. It causes a serious oriental disease known as kala-azar, which is accompanied by swellings, fever, enlargement of liver and spleen and the skin colour turns black.
Trypanosoma cruzi causes Chagas disease, and both Trypanosoma brucei and Trypanosoma gambiense cause African sleeping sickness.