548 FAMILY: TRYPANOSOMIDiE 



Hearsey (1909) was the first to report cases of human trypanosomiasis 

 from districts in which G. palpalis was not known to occur, and to susj^ect 

 the existence of a disease distinct from the well-known sleeping sickness. 



Relation to T. brucei of Animals and T. gambiense of Man.— Though the 

 characters of the tryj^anosome as described by Stephens and Fantham 

 serve to distinguish it from T. gambiense, this is not so for T. brucei in 

 animals, which it resembles so closely as to be morphologically indis- 

 tinguishable. The difficulty in dealing with this trypanosome is that there 

 is a divergence of opinion as to whether it is distinct from T. brucei or not. 

 Bruce and his co-workers (1913e) in Nyasaland came to the conclusion 

 that no differences exist between the trypanosomes producing disease 

 in man and animals, and wrote of it as T. brucei vel rhodesiense. The 

 trypanosome of Nyasaland was also found to be identical with a strain of 

 T. brucei from Zululand, from which country the original T. brucei came. 

 This similarity ap|)lies to all stages of the organism, whether in man, wild 

 game, experimental animals, or tsetse flies, so that there seems no reason 

 to regard T. rhodesiense as being distinct from T. brucei. Kinghorn and 

 Yorke (1912) arrived at the same conclusion in Rhodesia. It is, however, 

 a well-known fact that in many localities where nagana is widespread 

 amongst animals, and where human beings are constantly bitten by 

 G. morsitans which are actually transmitting T. brucei to animals, no 

 cases of human infection have been recorded. Moreover, in those districts 

 in which trypanosomes of this type produce disease in both man and 

 animals the number of human cases is much lower than those in animals. 

 Some observers, as, for instance, Taute (1913), Kleine (1914), Beck (1914), 

 believe that the human cases in these areas are due to a distinct trypano- 

 some, T. rhodesiense, and the animal cases to T. brucei. Kleine (1923) 

 again makes this assertion, and concludes that an animal reservoir of 

 T. rhodesiense is unknown. Those who regard the trypanosomes as 

 identical suppose that man is much less susceptible to infection than 

 animals. Furthermore, it has been suggested that this type of human 

 trypanosomiasis is a new disease, and there is some evidence in support of 

 this view. It is conceivable that it was only in one area that T. brucei 

 became capable of infecting man, and that, having once acquired this 

 property, the particular strain has now commenced to extend to other 

 areas. 



Taute believes the two trypanosomes are distinct, not only for the 

 reasons given above, but from the results of a series of experiments con- 

 ducted by himself and Huber (1919). A large number of human beings, 

 natives of Africa belonging to different tribes, to the number of 129, 

 and also the two observers themselves, were inoculated with T. brucei 

 derived from four horses and two mules which were discovered naturally 



