486 PROTOZOA 



Trypanosoma Brucei (Plimmer and Bradford) . 



The trypanosoma Brucei (Plimmer and Bradford) was discovered 

 by Bruce in 1894 in the blood of horses and cattle suffering from nagana 

 in Zululand and other parts of Africa. Bruce demonstrated that the 

 contagion was caused by the bites of a fly, the Glossina morsitans, or 

 tsetse-fly. Since then other varieties of flies also have been shown to 

 spread the disease. These flies bite by day and in full moonlight. The 

 infectivity of the insects lasts for about forty-eight hours after they have 

 bitten a sick animal. Bruce found living trypanosomes in the proboscedes 

 of the flies at the end of that time. Up to one hundred and eighteen hours 

 they were found in the flies' stomachs, but after one hundred and forty 

 hours the stomachs were empty and what appeared to be dead para- 

 sites were found in the excreta. No development in the fly has been 

 observed. The disease is chronic enough in some animals to account 

 for a continuous source of infection. The natural hosts of this species 

 are horses, cattle, camels, antelopes, swine, and various wild animals. 

 According to Laveran and Mesnil all mammifera are susceptible to 

 trypanosoma Brucei, though sheep and African goats seem to be 

 partial exceptions. Men and birds seem to be immune. Horses and 

 dogs are especially susceptible. The incubation time in natural infec- 

 tion is not more than nine days. The course and duration are irregular, 

 as in other trypanosomatic diseases. 



Novy and MacNeal have been successful also in cultivating the try- 

 panosoma Brucei in vitro, though it is much more exacting in its re- 

 quirements than is the trypanosoma Lewisi. The same methods are 

 used, but the blood dilution must not be less than two parts to one of 

 nutrient agar. These investigators state that the cultural characteristics 

 are such as to enable perfect differentiation between the two trypano- 

 somes. For in their cultures the trypanosoma Brucei have characteristic 

 granules, the trypanosoma Lewisi have none; the trypanosoma Brucei 

 show little variation in size (15;* to 17/* in length), the trypanosoma 

 Lewisi vary so much (I/* to 60ju long) that there are forms small enough 

 to pass a Berkefekl filter; the trypanosoma Brucei has a slow, wriggling 

 motion, the trypanosoma Lewisi moves with great rapidity and in an 

 almost straight line; and finally the trypanosoma Brucei form small, 

 irregular colonies, while the trypanosoma Lewisi form large symmetri- 

 cal ones. 



The question as to the identity of the trypanosoma Brucei with other 

 of the more pathogenic trypanosomes has not yet been decided. 



So far it^has not been possible to immunize the more susceptible 

 animals against this species of trypanosome. Sheep, goats, and cattle 

 are less susceptible and in their case recovery from the disease protects 

 against subsequent inoculation. 



Novy and MacNeal state that older cultures of trypanosoma 

 Brucei, especially those exposed to a temperature of 34 C., become 

 less virulent and eventually, though living, fail to infect animals, and 

 they think that repeated injections of these attenuated cultures may 



