Fantham and Porter120 (1914–15) have shown that young mice may be inoculated or fed with Herpetomonas jaculum, from the gut of the Hemipteran, Nepa cinerea (the so-called “water-scorpion”), with fatal results. The pathogenic effects are like those of kala-azar. They also showed that the post-flagellate stages of the herpetomonads seemed most capable of developing in the vertebrate.
A herpetomonad, H. davidi, has been found in the latex of species of the plant-genus Euphorbia in Mauritius, India, Portugal, etc. It is apparently transmitted to the plants by Hemiptera. The plants sometimes suffer from “flagellosis.”
Franchini (1913)121 has described a new parasite, Hæmocystozoon brasiliense, from the blood of a man who had lived in Brazil for many years. It possesses flagellate and rounded stages, and is closely allied to the herpetomonads.
Genus. Crithidia, Léger, 1902, emend. Patton, 1908.
Crithidia is the generic name of vermiform flagellates with a central nucleus, a blepharoplast or kinetic nucleus in the neighbourhood of the principal nucleus, and a rudimentary undulating membrane bordered by a flagellum arising from a basal granule, which is the centrosome of the kinetic nucleus (fig. 49b). The anterior or flagellar end of the body is attenuated and fades off as the undulating membrane.
Crithidia fasciculata, the type species, was found by Léger in the alimentary canal of Anopheles maculipennis. Crithidia occur in bugs, flies, fleas,122 and ticks. Some of them are found in the body-fluid of the invertebrate host as well as in the gut. Others may be restricted to the body cavity or intestine respectively. C. melophagia from the sheep-ked, Melophagus ovinus, and C. hyalommæ from the hæmocœlic fluid of the tick, Hyalomma ægyptium, pass into the ovaries and eggs of their hosts, and the young keds or ticks are born infected.
C. fasciculata has been shown by Laveran and Franchini to be inoculable into white mice, producing a sort of experimental leishmaniasis therein. In one case cutaneous lesions were produced like those of Oriental sore.
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.
Genus. Leishmania, Ross, 1903.
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.
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.
Fig. 50.—Leishmania donovani. 1, Free forms, each with nucleus and rod-shaped blepharoplast (after Christophers); 2, endothelial cell and leucocytes containing parasites (after Christophers); 3, capillary in the liver showing endothelial cells containing parasites (after Christophers); 4, two parasites escaping from a leucocyte in the alimentary canal of the bug (after Patton); 5, further development in bug (after Patton); 6, young flagellate forms in bug (after Patton); 7-11, culture forms (after Leishman); 7, 8, 9, show development of flagellum.
L. donovani can be cultivated in citrated splenic blood, under aerobic conditions, at 22° to 25° C. This was first accomplished by Rogers (1904). It is not so easily culturable as L. infantum on the Novy-MacNeal-Nicolle medium.124 L. donovani is inoculable with some difficulty into experimental animals—in India, white rats, white mice, dogs and monkeys (Macacus spp.), have been inoculated. The Sudan variety, somewhat less virulent, is inoculable to monkeys. Row also produced a local lesion in Macacus sinicus by subcutaneous inoculation of L. donovani. Parasites taken from such a local lesion were found to be capable of producing a generalised infection in Macacus sinicus and white mice.
In cultures the various species of Leishmania all grow into herpetomonad, uniflagellate organisms (fig. 50, 10), about 12 µ to 20 µ in body length. On this account Rogers125 and Patton place the Leishman-Donovan body within the genus Herpetomonas. The method of culture may be used in diagnosing leishmaniases.
Kala-azar is very probably an insect-borne disease. Patton126 suspects the bed-bug to be the transmitter and finds (fig. 50, 4-6) that the Leishman-Donovan body can develop into the flagellate stage in the digestive tract of the bed-bug. Feeding experiments are unsatisfactory, since there are very few cases in which the parasites occur in sufficient numbers in the peripheral blood to make the infection of the insect possible, or at any rate easy. In examining the alimentary tracts of insects for possible flagellate stages of Leishmania, it must be remembered that in many