Morphology.—As regards morphology it is usually stated that the parasites of the three species of Leishmania are practically identical. In cultures it has been noted that the flagella of L. tropica are longer and more twisted than those of L. infantum. Again it has been observed that the parasites of the Oriental and South American skin lesions may at times show a flattened or band-like trophonucleus instead of the constant round or oval one of the visceral leishmaniases.
Escomel has reported the finding of flagellated Leishmania in the South American sores.
Relationship.—Within the past year the view has been generally accepted that Indian kala-azar and infantile kala-azar are one and the same disease, the points of difference between L. donovani and L. infantum which had been advanced from cultural and animal inoculation standpoints having been disproved.
It has been suggested that the Mediterranean basin may have been the original focus of visceral kala-azar and that it spread thence to India by way of Greece and the Russian Caucasus, cases having been reported from districts which would join the two foci.
Just as children bear the brunt of malaria in old malarious districts and adults suffer in places in which the disease has been more recently imported, so by analogy we may consider the disease as of more recent introduction in India. We now know that visceral leishmaniasis is widely distributed in China, north of Yangtse, as well as in the Sudan, and quite recently a case of kala-azar has been reported from South America, in an Italian, who had lived in Brazil from 1897 to 1910.
In the Mediterranean basin there is a natural canine leishmaniasis and some think the human form may be contracted from the dog through the medium of the flea. This dog kala-azar exists in two types, one acute and the other chronic.
Some entertain the view that the virus of oriental sore is that of a modified visceral leishmaniasis and there has been experimental work along the line of determining whether the cutaneous infection immunized against the visceral or vice versa as with vaccinia and small pox.
Manson has suggested that as oriental sore is common in camel-using countries it might be that a passage through the camel lowered the virulence of the parasite as passage through the bovines does variola, so that such an infection was of a mild type.
More recently there has been some evidence to indicate that oriental sore may simply be a manifestation of a visceral infection as shown in Gonder’s work with mice and from the fact of the long period of incubation in oriental sore with the appearance in some cases of general symptoms as well as the cutaneous ones.
The South American leishmaniases differ clinically from oriental sore in that, following the primary lesions, ulcerating granulomatous processes of nasal and buccal cavities frequently set in subsequently, at times even after the primary manifestations have healed.