In studying certain infectious diseases of plants and in searching for animal parasites in the latex of various tropical plants in Central and South America, a flagellate parasite was discovered in three species of Euphorbiae. This flagellate is of the leptomonas type and is not dissimilar in appearance to the flagellate stage of Leishmania tropica giving rise to a form of tropical ulceration of the skin. In one district in Panama a very extensive phytodemic of the infection in Euphorbiae was found to exist. These plants were very abundant in this region and almost every one was found infected. The infected plants showed pathological changes, and the latex of the plant was also distinctly altered,—the flagellates causing disturbances in the circulation of the plant, sometimes forming emboli in the lactiferous channels. The nutrition of the plant was thereby distinctly disturbed and many of the plants became atrophied.
The insect Chariesterus cuspidatus transmitting the infection from the plant to a species of lizard Cnemidophorus lemniscatus was also discovered. From extensive experiments upon animals it was demonstrated that the flagellate as it occurs in the plant and also in the intestinal tract of the insect, is not pathogenic for vertebrates. However, after the flagellate has passed through the insect to the lizard, it acquires pathogenic properties and may give rise to a form of tropical ulceration in the skin, as was demonstrated from experiments in the monkey. In this ulceration the leishmania form of the parasite and not the flagellate stage is encountered.
There is perhaps nothing very extraordinary in the idea that a flagellate found producing a disease in plants may after passing through an invertebrate and a vertebrate host, acquire pathogenic properties for a mammal. This apparently is the first instance of this nature in which such a chain of infections has been demonstrated.