Leishmania infantum is the causative agent of infantile visceral leishmaniasis in the Mediterranean region and in Latin America, where it has been called Leishmania chagasi.
Leishmania donovani is a species of intracellular parasites that cause the disease leishmaniasis. The parasite is prevalent throughout tropical and temperate regions including Africa (mostly in Sudan), China, India, Nepal, southern Europe, Russia and South America.
The parasite requires two different hosts for a complete life cycle, humans as the definitive host and sandflies as the intermediate host. In some parts of the world other mammals, especially canines, act as reservoir hosts. In human cell they exist as small, spherical and unflagellated amastigote form; while they are elongated with flagellum as promastigote form in sandflies.
They are the causative agent of visceral leishmaniasis, traditionally known as kala-azar (“black fever”, particularly in India), because of its characteristic symptoms. The disease is highly lethal if not treated properly.
The two main tissues of infection are spleen and liver. Clinical symptoms include pyrexia (recurring high fever which may be continuous or remittent), enlargement of spleen and liver, and heavy skin pigmentation which darkens the physical appearance (the reason for naming “black fever”). To a lesser extent mucosa of the small intestine and lymph nodes are also invaded by the parasite.