The earliest discovered Trypanosome, described by Gruby in 1843 as “Trypanosoma sanguinis” and found by him in the blood of the common esculent Frog.
It was not noticed again until it was re-discovered by Lankester in 1871, who published the above figure of it in the Quarterly Journal of Microscopical Science in that year.
As to the parasite itself—the trypanosome—a long and very interesting story has now to be told. The first blood-parasite ever made known to naturalists and medical men was that to which Gruby, in 1843, gave the name Trypanosoma sanguinis. He found it in the blood of the common frog. We have here reproduced a figure of this original trypanosome ([fig. 49]). Similar parasites had been seen, but not named, in the blood of fishes. These trypanosomes are all very minute and of a somewhat elongated form, a fair average length being one thousandth of an inch. They are simple protoplasmic animals, consisting of one single nucleated corpuscle. The protoplasm is drawn out at one end of the creature into a motile undulating thread, and from the point where this joins the body a membranous undulating crest extends along the greater part of the animal’s length. There is no mouth, nutrition being effected by the imbibition of soluble nutrient matter.
After a long interval Gruby’s trypanosome was re-discovered in 1871; and then several kinds were described in the blood of tortoises, fishes and birds. In 1878, Dr. Timothy Lewis found a parasite in the blood of rats, at first in India, and subsequently in the common rats of London sewers. This parasite resembles a trypanosome in many respects ([fig. 46A]), but was very properly given a distinct name by Savile Kent, who called it “Herpetomonas.” This name has, however, been dropped; and the rat’s-blood parasite is spoken of as a trypanosome. It is the Trypanosoma Lewisii, and was the first of these trypanosomes to be found in the blood of a mammalian animal. The Trypanosoma Lewisii of the rat’s blood seems to do no harm to the rat, in which it swarms, multiplying itself by longitudinal fission; nor is it at present known to produce any trouble in other animals when transferred to their blood. Similarly, the frog’s trypanosome seems to exist innocently in the frog’s blood.
The next trypanosome discovered (1880) was, however found in the blood of camels, horses, and cattle suffering from a deadly disease known in India by the name “surra.” It is called Trypanosoma Evansii, after the observer who detected it. Trypanosomes now began to get a bad name, for the next was discovered in animals afflicted by a North African disease known to French veterinaries as “dourine.” This trypanosome was called T. equiperdum.
A little later, namely, in the year 1895, came Bruce’s discovery of a trypanosome associated with a tsetze fly in the production of the terrible nagana disease of the “fly-belts” of South Africa, which renders whole territories impassable for horses or cattle ([fig. 46B]). The remarkable and important observation was made by Bruce that this trypanosome (known as T. Brucei) inhabits the blood of big game without injuring them, just as the rat’s trypanosome inhabits the rat’s blood without producing disease; and that it is only when the trypanosome is carried from these natural wild “hosts” to domesticated animals introduced by man, such as horses asses, cattle, and dogs, that disease results. The wild animals are “immune” to Bruce’s trypanosome; the introduced animals are poisoned by the products of its growth and fissile multiplication in their blood.
Since Bruce’s researches on nagana, a trypanosome, T. equinum ([fig. 46D]), has been discovered in the horse-ranches of South America, where it causes deadly disease, the mal de caderas, among the collected horses; and a curiously large-sized trypanosome has been found by Theiler in the blood of cattle in the Transvaal. Down to a recent date no trypanosome had been found in the blood of man; and indeed it is almost certain that none of the kinds hitherto mentioned can survive in his blood. But in 1902 Dutton discovered a trypanosome in the blood of a West African patient; and a few other cases were noted. This trypanosome of human blood was called by Dutton T. Gambiense. It was not found to be connected with any serious symptoms, a little fever being the only disturbance noted. It now, however, appears that this trypanosome in the blood is the preliminary stage of the infection which ends in sleeping sickness; and, as we have seen, in a population seriously attacked by sleeping sickness, as is that of Uganda, as many as 28 per cent. of the people have trypanosomes in their blood.
There is no ground at present known for distinguishing Dutton’s T. Gambiense of human blood from that which Bruce has found to be so terribly abundant in Uganda, and to be the cause of sleeping sickness. Indeed all the trypanosomes of the blood of the larger mammalia are singularly alike in appearance; and the figure which is here given ([fig. 50]) of the trypanosome of sleeping sickness (T. Gambiense) might quite well serve to represent the T. Evansii of surra disease, the T. Brucei of nagana disease, or the T. equinum of the South American mal de caderas.