HUMAN DISEASES 529 



The work in Uganda and Nigeria has been concerned primarily 

 with the form of sleeping sickness caused by Trypanosoma gambiense 

 and conveyed by the tsetse fly, Glossina palpalis , to which must be 

 added G. tachinoides in Nigeria. In Tanganyika the other variety 

 of the disease, caused by T. rhodesiense and conveyed by G. swyn- 

 nertoni and G. morsitans is the major problem; the area of infection 

 is enormous and huge tracts of country are rendered uninhabit- 

 able. Studies in that territory have, of course, been closely associ- 

 ated with the tsetse department under the late Mr. Swynnerton 

 (1936). A summary of work at these three centres may serve to 

 supplement the account of research on tsetse flies in Chapter X 

 and of animal trypanosomiasis in Chapter XIV. 



The results from Uganda have been published in annual reports 

 (Uganda 1933-4, A.R.) and in numerous scientific papers, and 

 the following salient conclusions have been reached. Regarding 

 the transmission of the disease, infection by trypanosomes exerts 

 no apparent effect on the longevity of G. palpalis, and there is no 

 difference in the susceptibility of the two sexes of this fly to man's 

 trypanosomes. A mass of evidence has been produced to show 

 that there occur in man in Uganda and elsewhere strains of T. 

 gambiense which, from their first isolation, are non-transmissible by 

 Glossina. G. morsitans has been shown to be a better transmitter 

 of the trypanosomes of man than G. palpalis. Repeated cyclical 

 passage through Glossina does not necessarily increase the trans- 

 missibility of a strain of trypanosomes. Old laboratory strains of 

 man's trypanosomes have been found to be non-transmissible by 

 tsetse; a strain of T. gambiense, maintained for fifteen years in 

 laboratory rodents, was tested on man and found to be readily 

 pathogenic. T. rhodesiense has been transmitted readily from host 

 to host by the direct method, by Stomoxys and also by feeding 

 infected prey to carnivorous animals. 



The part played by domestic and wild animals in serving as 

 reservoirs for human trypanosomes has likewise been examined, 

 with the following results: natural immunity against T. gambiense 

 in sheep and goats varies from complete immunity to a degree of 

 susceptibility in which the trypanosomes may be a contributory, 

 or even the direct cause of death. Between these extremes there 

 usually exists partial immunity, which prevents the transmission 



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