(surra), T. hippicum (murrina, a disease of mules in Panama), T. equinum (mal de caderas), T. equiperdum (dourine, or mal du coït), T. vivax vel cazalboui (souma disease of mules and cattle in the Soudan).
These trypanosomes are all about the same size (22-28 μ in length and 1-3 μ in breadth). The aflagellar extremity is blunted to a variable extent, the nucleus is centrally placed, and the protoplasm granular. For further details of the members of this group, see p. 194.
According to some authors, T. dimorphon, a parasite of horses in the Gambia, producing symptoms resembling nagana, represents a distinct type. As its specific name implies, it is found in two distinct forms—one long form, 22 μ in length; and a short, stumpy form, 1-5 μ in length. The aflagellar extremity is markedly blunted, and the body protoplasm is continued to the end of the flagellum.
T. nanum resembles T. dimorphon in general features, and is the smallest of all the mammalian trypanosomes, measuring 11-16 μ by 2·5 μ. It produces a chronic disease, marked by emaciation and anæmia, in cattle in the Soudan.
T. theileri (Fig. 231), 60-70 μ in length by 4 μ in breadth,
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| Fig. 231. T. theileri. (After Laveran.) |
Fig. 232. T. lewisi. (After Laveran.) |
Fig. 233. T. brucei. (After Laveran.) |
one of the largest mammalian trypanosomes, is recognized by its large size and rapid movements. It is apparently non-pathogenic, and is transmitted, according to Theiler, by Hippobosca rufipes. T. ingens, found in cattle in Uganda, is still larger than T. theileri, measuring 72-122 μ in length, and the flagellum alone measuring 17 μ.
The transmission of these trypanosomes from one host to another is carried out, so far as is known, by the agency of some blood-sucking invertebrate. When such a host is of terrestrial habit the definitive host is an insect, when aquatic a leech; though in one species, T. equiperdum, the cause of "dourine" in horses, the trypanosomes may pass from one host to another during coitus. Hereditary transmission in trypanosomes has not yet been proved. One or more species of insect may serve as the definitive host; thus in T. lewisi the selective hosts are the rat-fleas (Ceratophyllus fasciatus and Xenopsylla cheopis), though it may also develop in a different genus, the rat-louse (Hæmatopinus spinulosus), and also in Pulex irritans and Ctenocephalus canis.
The life cycle in the vertebrate host is generally as follows: After infection (as in T. lewisi, Fig. 232) the trypanosomes appear in the blood about the fifth to the seventh day. Owing to the rapidity with which fission takes place, the
