Crithidia are natural flagellates of Arthropoda, with their own pre-flagellate, flagellate and post-flagellate stages, and must not be confused with transitory crithidial stages of trypanosomes.
With an oval body containing nucleus and blepharoplast (kinetic nucleus) but no flagellum. An intracellular parasite in the vertebrate host.
Included in the genus _Leishmania_ are three species, namely:--
(1) _Leishmania donovani_, Laveran and Mesnil, 1903, the parasite of Indian kala-azar, a generalized systemic disease, usually fatal, occurring in subjects of all ages. (2) _Leishmania tropica_, Wright, 1903, the parasite of Delhi boil, Oriental sore, Aleppo button--a localized, cutaneous disease, usually benign. (3) _Leishmania infantum_, Nicolle, 1908, the parasite of infantile kala-azar, occurring in children (and a few adults) around the shores of the Mediterranean. The disease is perhaps a form of Indian kala-azar, and the parasite is probably identical with _L. donovani_.
These diseases may be termed collectively leishmaniases. The morphology of the various species is practically identical.
*Leishmania donovani*, Laveran and Mesnil, 1903.
Syn.: _Piroplasma donovani_, Laveran and Mesnil.
The parasite of Indian kala-azar was demonstrated in 1900 by Leishman from a _post-mortem_ examination of a case of “Dum-Dum fever,” but details were not published till May, 1903. In July, 1903, Donovan found similar bodies from cases in Madras. Rogers succeeded in cultivating the parasite in July, 1904.[123] The original centre of the disease was probably Assam; it occurs also in Madras, Ceylon, Burma, Indo-China, China and Syria. A variety of this leishmaniasis is found in the Sudan. The patient becomes emaciated, with a greatly enlarged spleen. There is anæmia and leucopenia.
[123] The literature up to 1912, on kala-azar and other leishmaniases is reviewed in the _Kala-azar Bulletin_. Afterwards in the _Tropical Diseases Bulletin_.
The parasite, commonly known as the Leishman-Donovan body, is intracellular (fig. 50, 2, 3). It is found in the endothelial cells of the capillaries of the liver, spleen, bone-marrow, lymphatic glands and intestinal mucosa, and in the macrophages of the spleen and bone-marrow. Some host cells may contain many parasites. It is rather rare in the circulating blood, but may be found in the blood from the femoral, portal and hepatic veins. It does not occur in the red blood corpuscles as was formerly thought. The parasites liberated from the endothelial cells are taken up by the mononuclear and polymorphonuclear leucocytes. The Leishman-Donovan body is the resting stage of a flagellate. As found in man it is a small, oval organism, about 2·5 µ to 3·5 µ in length by 2 µ in breadth, and containing two chromatinic bodies, corresponding to the nucleus and kinetic nucleus (blepharoplast) of a flagellate. The latter element is the smaller and more deeply staining, and is usually placed at the periphery, transversely to the longer axis of the oval organism. There is sometimes a very short, slightly curved filament to be seen, which may be a rhizoplast. Multiplication takes place by binary or multiple fission. The presence of the parasite used to be demonstrated by splenic or hepatic puncture; nowadays it can be demonstrated in peripheral blood, _e.g._, of the finger, or by culture of infected blood.