SLEEPING SICKNESS 



147 



2. The Trypanosomidae are flagellate Protozoa, chiefly 

 parasitic in the blood of higher Vertebrates and the ali- 

 mentary canal of Invertebrates. A typical fully formed 

 trypanosome is seen in Fig. 69 (i), but there may be great 

 variation of shape at different stages of the life-history, 

 even rounded non-flagellate stages occurring {Leishmania) . 

 The curved-blade-like cell has a single flagellum rising 

 from a base termed the blepharoplast, and for part of its 

 length joined to the rest of the cell by a thin undulating 

 membrane. Near the blepharoplast is a small nucleus- 

 like body. There is also a prominent central nucleus. 

 Vacuoles and granules may be present in the cytoplasm. 

 A delicate " periplast " covers the outside of the cell. 

 Reproduction is by longitudinal division, beginning at the 

 basal end of the flagellum. 



Trypanosomes have been found in the blood of many 

 mammals, including mice, voles, rabbits, cavies, squirrels, 

 various bats, moles, shrews, ant-eaters, badgers, marmosets, 

 monkeys, armadillos, as well as the better-known hoofed 

 animals. They are also found in birds, reptiles, 

 amphibians, and a great many fishes. They are spread 

 from one host to another by means of an intermediate 

 host, usually a blood-sucking insect or leech, within which 

 a phase of the life-history is passed. A few occur in plants ! 



T. gamhiense multiplying in the blood causes African 

 sleeping sickness. It is transmitted by a tsetse fly. T. 

 brucei, also carried by a tsetse fly, and a most virulent 

 trypanosome, causes Nagana in, chiefly, domestic stock. 

 Its " natural " hosts are certain of the bigger African game 

 animals which seem to be unaffected by it. T. equiperdum 

 causes dourine in horses. T. evansi, a trypanosome 

 affecting horses, camels, mules, domestic cattle, and dogs 

 in tropical countries, causes the disease known as " Surra," 

 especially deadly amongst horses. _,In 1907 T. cruzi was 

 discovered by Chagas in South America. It chiefly affects 

 children and adolescents, causing Chagas' disease. It is 

 transmitted by a bug. The commonest trypanosome is 

 that found in the blood of rats — T. lewisi — and transmitted 

 from rat to rat by fleas. When infected blood is sucked 

 in by the flea, the trypanosomes pass from the cavity of 

 the flea's stomach and burrow into the lining cells of 



