The Herpetomonads occur principally in the digestive tracts of insects, such as Diptera and Hemiptera. They are also known in the guts of fleas and lice, but are not confined to blood-sucking insects. One example, H. ctenocephali (Fantham, 1912)[117] occurs in the digestive tracts of dog fleas, Ctenocephalus canis, in England, France, Germany, Italy, India, Tunis, etc. It is a natural flagellate of the flea, and might easily be confused with stages of blood parasites in the gut of the dog flea. Dog fleas are stated by Basile to transmit canine kala-azar, which is believed to be the same as human infantile kala-azar. Confusion is further likely to arise since herpetomonads pass through pre-flagellate, flagellate and post-flagellate or encysted stages; pre- and post-flagellate stages being oval or rounded and Leishmania-like. The post-flagellate stages are shed in the fæces, and are the cross-infective stages by means of which new hosts are infected by the mouth. The possible presence of such natural flagellates must always be considered when experimenting with fleas, lice, mosquitoes, etc., as possible vectors of pathogenic flagellates like Leishmania and Trypanosoma. H. pediculi (Fantham, 1912) occurs in human body lice.[118] See further remarks on pp. [107], [112].
Fig. 49.—a, Herpetomonas; b, Crithidia; c, Trypanosoma. (After Porter.)
Laveran and Franchini (1913–14)[119] have recently succeeded in inoculating Herpetomonas ctenocephali, from the gut of the dog flea, intraperitoneally into white mice, and producing an experimental leishmaniasis in the mice. A dog was also infected. They have also succeeded in infecting mice with H. pattoni—a natural flagellate of the rat flea—by mixing infected rat fleas with the food of the mice, and by causing them to ingest infected fæces of rat fleas. Further, they have shown that infection with the herpetomonas occurs naturally by this method, that is, by the rodents eating the fleas and not by the insects inoculating the flagellates into the vertebrates when sucking blood. These experiments shed an interesting light on the probable origin of Leishmania and its cultural herpetomonad stage, which were very probably once parasitic flagellates in the gut of an insect.
Fantham and Porter[120] (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.