Trypanosome

“ In experimental rats it has been found possible to transmit infection to other rats through the unbroken skin by rubbing on cultures of this trypanosome.
It is generally held that T. lewisi is non-pathogenic. Certainly, infected rats usually exhibit a remarkable tolerance towards this parasite, but occasionally they do sicken and die.
The fact that the rat is susceptible to laboratory inoculation with the trypanosomes of man and cattle indicates the possibility of finding other species of trypanosomes in the blood of wild rats. ”

“ Note: Escomel has reported the finding of a trypanosome 20 to 40 microns by 3 to 4 microns which had a flagellum as long as the body and with a very small but distinct blepharoplast (unlike S. cruzi) in the blood of a native of Peru. The patient at the time of the blood examination was afebrile and showed a generalized firm oedema. There was noted anaemia, prostration and somnolence. This may be a new species.
TRYPANOSOMIASES OF ANIMALS
Trypanosoma brucei.—This trypanosome causes a surely fatal disease in horses and one from which few cattle recover. ”

“ In considering the occurrence of Trypanosomes in mammals, careful distinction must be drawn between natural or true hosts, which are tolerant of the parasites, and casual ones, which are unaccustomed and unadapted to them. A Trypanosome usually produces markedly harmful effects upon gaining an entry into animals which have never been, by their distribution, liable to its invasion previously. ”

“ The development of an indifferent ookinete into an indifferent Trypanosome is shown in fig. 7, from which it will be seen that the cytological details are very complex, The indifferent parasites exhibit an alternation of resting, attached phases with active periods, during which they multiply actively and become very abundant in the insect. The male forms, which are very small and the homologies of the micro gametes developed in the blood, appear to die off soon. The female Trypanosomes, on the other hand, grow to a large size, laying up a store of reserve nutriment. ”

“ Probable synonyms.—Trypanosoma dimorphon, Laveran and Mesnil, 1904; Trypanosoma nanum, Laveran, 1905; Trypanosoma pecorum, Bruce, 1910; Trypanosoma confusum, Montgomery, 1909.
This trypanosome causes disease among horses (e.g., Gambia horse sickness) , cattle, sheep, goats, pigs, and dogs. It is widely distributed in Central Africa (e.g., Gambia, Congo, Uganda, Nyasaland) , the strain probably being maintained naturally in big game. It is transmitted by various Glossinæ, and perhaps by Tabanus and Stomoxys. It is said to develop in the gut and proboscis of Glossina palpalis and G. morsitans. ”

“ Some of the Lithuanian bison have lately been dying in an unaccountable way, and on investigating a dead individual a Russian observer has discovered a "trypanosome" parasite in the blood. The trypanosomes are microscopic corkscrew-like creatures, of which many kinds have become known within the last ten or fifteen years. They are "single cells"—that is to say, "protoplasmic" animalcules of the simplest structure—provided with [Pg 267] a vibrating crest and tail by means of which they swim with incessant screw-like movement through the blood. ”

“ History.—— Although its true etiology was not apprehended until quite recently, sleeping sickness, the terminal phase of African trypanosomiasis, has been known for over a century.
The occurrence of trypanosomes in animals has been recognized for at least sixty years, first in cold-blooded vertebrates, later in mammals. The best-known and first-described mammalian species is that of the rat (Trypanosoma lewisi) . It was discovered by Lewis, in 1879, in Calcutta. In the following year Evans described a similar parasite (T.evansi) in the blood of horses in India ”

“ Similarly with regard to the many other pathogenic Trypanosomes now known, there is undoubtedly, in each case, some indigenous wild animal tolerant of that particular form, which serves as a “latent source of supply” to strange mammals.
The transmission of the parasites from one vertebrate individual to another is effected, in the great majority of cases [3] by a blood-sucking invertebrate, and by this means minion; alone. The “carrier” of a Trypanosome of warm-blooded vertebrates is, in all instances so far described,Transmission: Alterations of Hosts. ”

“ Experiment has shown that the glossina will bite any vertebrate, and that it can infect a large variety of mammals with the trypanosome. If this be the case in the laboratory it is reasonable to suppose that it is the case in nature also. Therefore, in the endemic regions of trypanosomiasis, the vertebrate fauna has to be reckoned with as a source and reservoir of infection. ”

“ Treatment.—— Although something may be done to relieve symptoms and delay the fatal issue in the sleeping-sickness stage of trypanosomiasis, it is only in the earlier stages of the infection and by the persistent and energetic use of arsenic or antimony, or both, that a cure can be effected, and that in a proportion of cases only. Other drugs have been shown to have some influence on the trypanosome infections of the lower animals, but their therapeutic value in those of man is practically negligible. ”

“ The passage through the crithidial stage is characteristic of the salivary development, and the trypanosome forms just mentioned are derived from the crithidial types. The development in the salivary gland takes from two to five days before the forms are infective.
"9. The fly is never infective until the glands are invaded. Trypanosomes from the proventriculus when injected into a monkey never produce infection. Trypanosomes may be found in the salivary glands as early as the sixteenth day of the cycle. ”

“ Then (1909) came the important discovery by Kleine that the tse-tse fly was no mere mechanical transmitter of the trypanosome, as had been supposed, but was a true intermediate host. Later, on morphological and clinical grounds, Stephens and Fantham established the existence in Rhodesia of another species or variety of trypanosome (T. rhodesiense) , which Kinghorn and Yorke have since proved to be transmitted by Glossina morsitans. ”

“ Also, it was found that trypan red was a curative agent only for the infection in mice; on the trypanosome diseases of larger animals, as horses and cattle, it had no curative effect. However, the experience with trypan-red pointed the way to a solution of the difficulty; either a drug must be found which by a single injection would kill every parasite, or several different drugs must be used, which, acting on the same parasite, and thus allowing a combination treatment, would lead to a cure without the danger, to the host, of a single massive dose. ”

“ 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. ”

“ Castellani was still at Entebbe engaged in the study of his streptococcus. He mentioned to Colonel Bruce on his arrival that he had on more than one occasion seen a trypanosome in the cerebro-spinal fluid of negroes suffering from sleeping sickness; but, inasmuch as Dutton on the West Coast and Hodges in Uganda had described a trypanosome as an occasional parasite in human blood, he had not considered its occurrence in sleeping-sickness patients as of any more significance than is the occurrence of Filaria perstans. ”

“ In long generations of suffering the African big game has won for itself the power of resisting the trypanosomes. Although the trypanosomes abound in their blood, the wild animals do not develop "nagana" or "surra," the diseases which the tsetse bite sets up in most domestic animals. Something has been bred into their beings which checks the trypanosome's power. The animals are immune, or salted. ”

“ Subsequent growth results in the production of the typical trypanosome form, which re-enters the circulating blood and multiplies by longitudinal binary fission. Division of the parasite prior to the formation of a latent body may occur and division of the latent forms themselves is known, though less common. ”

“ Trypanosomes vary greatly with regard to size; even in one and the same species this variation is often noticeable, especially under Mon, , w, oD, different conditions of life. The common Trypanosoma rotatorium of frogs (fig., A and B) is, taking it all in all, one of the largest forms so far described. Its length (inclusive of the flagellum) varies from 40-60 p, while its greatest width (including the undulating-membrane) is from 8-30, a; in the very wide individuals breadth is gained more or less at the expense of length. ”

“ Very many of the common domestic mammals can be successfully infected (either thus accidentally or else on purpose) with different “pathogenic” Trypanosomes, to which they succumb more or less readily, but they cannot be regarded as the natural hosts of those Trypanosomes. In dealing with disease-causing forms, the more narrowly the original source of the parasite concerned is defined, the closer do we get to the true vertebrate host or hosts. ”

“ The chronic form is that most commonly encountered in youths or adults; it is probably carried on from infancy or childhood, or kept up by reinfection.
The parasite.— During the febrile attacks the parasite (Fig. 51) in variable numbers is to be found in the blood, free or, rarely, partially included in red blood-corpuscles (Chagas) . It averages about 20/u in length and has the usual trypanosome characters. The undulating membrane is narrow and the nucleus and blepharoplast are large. It is easily cultivated.
After ingestion by the insect intermediary the trypanosomes multiply in the gut. ”

“ The body is probably not limited by any distinct membrane. The cytoplasm is finely granular and fairly uniform in character. The most interesting point about the morphology is the fact that two chromatic bodies, of very unequal size, are almost invariably to be recognized. The larger nuclear body, which corresponds to the trophonucleus of a Trypanosome, is usually round or oval; the smaller one, representing a kinetonucleus, has the form either of a little rod or of a round grain, and is generally separate from the larger nucleus. ”

“ Exophthalmos was noted 16 times. ↑ * The Wassermann reaction is of little avail, as unfortunately the sera of most cases of trypanosomiasis give a positive result. ↑ * Broden and Rodhain report good results on the Congo by intravenous injection of salvarsan; they insist that it is only of benefit in those cases where invasion of the spinal cord is negatived by microscopical examination of the spinal fluid. ↑ * Duke has tried the injection of prophylactic doses of arseno-phenylglycin in the monkey and subsequent development of the trypanosome in the tse-tse fly. ”

“ An interesting fact pointed out by Ehrlich is that the parasites can get used to a drug and become resistant. It is therefore advisable to alternate various trypanocidal agents in the treatment as much as possible, that is, to give atoxyl, some other trypanosome-killing drug, and mercury; for instance, atoxyl, fuchsin, or some other colouring matter by the mouth, and sublimate. ”

“ The small Trypanosomes resulting from either of these modes of division differ from typical adults by their stumpy, pyriform shape, the position of the kinetonucleus near the flagellar end of the body, and the absence, during the first part of their youth, of an undulating-membrane. At this period they have, in fact, what may be termed a “pseudo-Herpetomonadine” aspect. These young individuals can themselves multiply by equal binary fission, giving rise to little fusiform parasites; with growth, these gradually assume the adult appearance. ”

“ Todd, J.L. A Note on Recent Trypanosome Transmission Experiments. Jour. Trop. Med. & Hyg., 12, Sept., 1909, p. 260. Show that they develop in G. palpalis when taken from their mammal host at the proper stage of development.
Woodcock, H.M. The Hæmoflagellates: a Review of Present Knowledge Relating to the Trypanosomes and Allied Forms. Quar. Jour. Micro. Sci., Vol. 50, 1906, pp. 151–331. Characteristics; mode of infection; effects on host; biological considerations; life-cycle, etc. Spirochaetæ; bibliography. Important article.
Trypanosomiasis and Sleeping Sickness. Jour. Trop. Med. ”

“ Although this class contains fewer forms than the preceding some of these have within recent years been found to be of great importance because they live as parasites on man and other animals. The trypanosome whose presence in the blood and tissues of the patient causes that dreadful disease which ends in sleeping sickness belongs here as well as do several other similar kinds that produce serious troubles for various mammals and birds. ”

“ Agglomeration consists in the grouping or union together of several Trypanosomes around a common centre; this leads to the formation of rosette-like clusters, or even of large masses composed of several rosettes. The end by which the parasites join is typically, in the case of Trypanosoma, the non-flagellate (anterior) end. If a favourable change in the surrounding medium sets in, the Trypanosomes are able to undergo the reverse process, namely dis agglomeration; the parasites liberate themselves and the rosette is dissolved. ”