The species complex it represents is prevalent throughout tropical and temperate regions including Africa (mostly in Sudan), China, India, Nepal, southern Europe, Russia and South America.

[5] L. donovani was independently discovered by two British medical officers William Boog Leishman in Netley, England, and Charles Donovan in Madras, India, in 1903.

Unlike other parasitic protists they are unable to directly penetrate the host cell, and are dependent upon phagocytosis.

[8] L. donovani sensu stricto is in a species complex with the closely related L. infantum, which causes the same disease.

[9] One of the earliest known epidemics of L. donovani infection (kala-azar as it was called in Hindi) was known in India just after the Indian Rebellion of 1857.

[10] In 1903, Leishman published his discovery as "On the possibility of the occurrence of trypanosomiasis in India" in the British Medical Journal, which appeared on 11 May.

Donovan sent some of his slides to Ronald Ross, who was at the time in Liverpool, and to Alphonse Laveran at the Pasteur Institute in Paris.

Laveran and his colleague Félix Mesnil identified the protozoan (and yet wrongly) to be members of Piroplasmida, and gave the scientific name Piroplasma donovanii.

It was Ross who resolved the conflict of priority in the discovery and correctly identified the species as member of the novel genus Leishmania.

He gave the popular name "Leishman-Donovan bodies", and subsequently the valid binomial Leishmania donovani, thereby equally crediting the two rivals.

[10][15][16] Leishmania donovani is a unicellular eukaryote having a well-defined nucleus and other cell organelles including a kinetoplast and a flagellum.

)[28] They then migrate back towards the anterior part of the digestive system such as pharynx and buccal cavity.

[16][29] The metacyclic promastigotes then enter the hollow proboscis where they accumulate and completely block the food passage.

[9] Although L. donovani is only the second-most prevalent Leishmania causing VL, it is the most dangerous form and directly fatal to humans.

[40] It is responsible for tens of thousands of mortality among Africans in eastern and southern parts of Sudan.

[41] Moreover, due to emergence of drug resistance the prevalence is not subsiding, and in fact has spread to central Europe.

[42] L. donovani is the causative agent of visceral leishmaniasis, traditionally known as kala-azar ("black fever", particularly in India), because of its characteristic symptoms.

[46] During phagocytosis by macrophages, the promastigotes inhibit the formation of the phagolysosome, a cellular product by which invading pathogens are removed.

[47] They are capable of evading the microbicidal actions of macrophages, which can kill ordinary pathogens using reactive nitrogen and oxygen intermediates.

[citation needed] To compound the situation, drug resistance has evolved in the parasites against the traditional antimonials.

Liposomal amphotericin B (L-AmB) has been a drug of choice in India, but is practically useless in Africa because of low effectiveness in the African strain of the parasite.

[51] In 1999, an anticancer drug miltefosine was demonstrated to be highly effective (95% cure rate) among Indian patients.

[55] DNA sequencing of different geographical strains indicates that the protozoan complex can be classified into two valid taxa, L. donovani and L. infantum.