The Animal Parasites of Man. Max Braun
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Название: The Animal Parasites of Man
Автор: Max Braun
Издательство: Bookwire
Жанр: Медицина
isbn: 4057664648037
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When infective forms of T. lewisi have been developed within the gut of a rat flea, they may enter and infect the vertebrate host by96 (a) being crushed and eaten by the rodent; (b) the rat may lick its fur on which an infected flea has just passed infective excrement; or (c) the rat may lick, and infect with flea excrement, the wound produced by the bite of the flea.
The time taken for the full development of T. lewisi in the flea is about six days. The intracellular phase is at its height about the end of the first day; the crithidial phase, in the flea’s rectum, begins during the second day; the stumpy, infective trypanosomes are developed in the rectum about the end of the fifth day.
Wenyon97 writes that, “the fleas, when once infected with T. lewisi, remain infected for long periods, for though many small infective trypanosomes are washed out of the gut at each feed, those that remain behind multiply to re-establish the infection of the hind gut. Further, the infection is still maintained even if the flea is nourished on a human being, so that fresh human blood does not appear to be destructive to the infective forms in the flea.”
The best method of controlling fleas during experiments is that due to Nöller. He adopted the method of showmen who exhibit performing fleas, and secure them on very fine silver wire.
Of fleas fed on an infected rat only about 20 per cent. become infective. About 80 per cent. are immune. If fleas are examined twenty-four hours after feeding, trypanosomes will be found in all, so that many of the parasites are destined to degenerate.
It may be of interest to note that Gonder98 (1911) has shown that a strain of T. lewisi resistant to arsenophenylglycin loses its resistance after passage through the rat-louse, Hæmatopinus spinulosus. These experiments suggest that physiological “acquired characters” may be lost by passage through an invertebrate host.
Trypanosoma brucei, Plimmer and Bradford, 1899.
Trypanosoma brucei was discovered by Sir D. Bruce in 1894 in cattle in Zululand and was named T. brucei by Plimmer and Bradford in 1899 in honour of its discoverer. This trypanosome is of considerable economic importance, as it is responsible for the fatal tsetse fly disease, or “nagana,” in cattle, horses and dogs. The disease is widely distributed in Africa and is transmitted from host to host by the tsetse, Glossina morsitans, and other species of Glossina. The virus is maintained in nature in certain big game, such as wildebeest, bushbuck and koodoo, which thus act as living reservoirs of disease from which the tsetse may become infected. These reservoir hosts are not injured, apparently, by the presence of the parasites.
T. brucei is rapidly fatal to the small laboratory animals, such as rats and mice. Horses, asses and dogs practically always succumb to its attacks, while a very small number of cattle recover from “nagana.” The disease is characterized by fever, destruction of red blood corpuscles, severe emaciation and by an infiltration of coagulated lymph in the subcutaneous tissue of the neck, abdomen and extremities giving a swollen appearance thereto. The natural reservoirs in which T. brucei has been long acclimatized are unaffected by the trypanosomes, while the newer hosts, such as imported cattle in Africa, are rapidly destroyed by their action.
Fig. 40.—Trypanosoma brucei. × 2,000. (After Laveran and Mesnil.)
The general morphology and life history in the vertebrate host is that of a typical trypanosome (fig. 40). Its length is from 12 µ to 35 µ, its breadth from 1·5 µ to 4 µ. Multiplication by longitudinal division proceeds in the peripheral blood (fig. 26), while latent, leishmaniform bodies are produced in the internal organs.
Bruce and colleagues99 have quite recently (June, 1914) described the development of a Zululand strain of T. brucei in G. morsitans. The tsetse flies were bred out in Nyasaland. In vertebrate blood the brucei strain was polymorphic. The development was like that found for T. gambiense in G. palpalis (fig. 30), and by Bruce and colleagues for T. rhodesiense in G. morsitans in Nyasaland. Long trypanosomes were found in the proventriculus of the tsetse. Crithidial, rounded or encysted, and immature “blood forms” occurred in the salivary glands; and finally infective, stumpy, “blood forms” were differentiated in the salivary glands. The period of development of T. brucei in G. morsitans takes about three weeks, and then the fly becomes infective. Bruce believes that T. rhodesiense of Nyasaland and T. brucei of Zululand are the same, their cycles of development in G. morsitans being “marvellously alike.” (But see Laveran, p. 80.)
T. brucei has been cultivated with difficulty by Novy and MacNeal, using blood agar. The best treatment for nagana is arsenic in some form.
It is probable that more than one trypanosome has been confused under the name T. brucei, more especially as the occurrence of many species of trypanosomes in various animals in Africa was not suspected until comparatively recent times. It has been shown by Stephens and Blacklock (1913) that the original Zululand strain of T. brucei was monomorphic, while the organism sent from Uganda, and at the time believed by Bruce to be the same as the Zululand trypanosome, has been found to be polymorphic, with morphological resemblances to T. rhodesiense. Stephens and Blacklock100 have suggested the name T. ugandæ for the polymorphic trypanosome, which, however, has marked resemblances with Trypanosoma pecaudi, and they are, perhaps, identical. T. pecaudi was the name given by Laveran101 in 1907 to the causal agent of “baleri” in equines and sheep in the French Sudan. T. pecaudi, which is dimorphic, is widely distributed in Africa. An extremely small number of both T. pecaudi and T. ugandæ have been shown to possess posterior nuclei. T. pecaudi is transmitted by various species of Glossina, and is said to develop in the gut and proboscis of the fly.
On the other hand, Bruce and colleagues (1914), examining a strain sent from Zululand in 1913, state that T. brucei is polymorphic. Bruce (1914) suggests that passage through laboratory hosts has influenced and altered the morphology of the parasite.
Trypanosoma evansi, Steel, 1885.
Syn.: Spirochæta evansi, Steel, 1885; Hæmatomonas evansi, Crookshank, 1886; Trichomonas evansi, Crookshank, 1886.
Trypanosoma evansi, first found by Evans in 1880, in India, is the causal agent of the disease known as “surra.” The malady affects more particularly horses, mules, camels and cattle in India and neighbouring countries, such as Burma and Indo-China. It occurs also in Java, the Philippines, Mauritius and North Africa. Elephants may be affected. A serious outbreak among cattle in Mauritius occurred in 1902, the disease being imported into the island. The symptoms are fever, emaciation, œdema, great muscular weakness and paralysis culminating in death.
T. evansi varies from 18 µ to 34 µ in length and 1·5 µ to 2 µ in breadth. It has a pointed posterior extremity, СКАЧАТЬ