106 



Just as yellow fever in the Panama zone has disappeared with the 

 destruction of mosquitos and African Coast fever and redwater have 

 been combated by the eradication of ticks, there is every reason to 

 believe that the disappearance of trypanosomiasis from Southern 

 Rhodesia will follow the discovery of a successful method of eradicating 

 the tsetse-fly. When the principles upon which natural resistance 

 depends are more thoroughly understood, there is every reason to 

 believe that most of the diseases of this type in man and the lower 

 animals will entirely disappear. 



Hornby (H. B.). Traasmission of Cattle Trypanosomes by Flies other 

 than Tsetse. — Rhodesia Agric. JL, Salisbury, xiv, no. 2, April 

 1917, pp. 168-176, 1 plate. 



Of the 50 odd species of trypanosomes commonly occurring in 

 mammalian blood throughout the world, less than a dozen are known 

 to be transmitted by tsetse- flies, a large proportion of them being found 

 in countries where no species of Glossina occur. 



The trypanosomes causing disease in man and domestic animals 

 in Central Africa have been classified by Bruce and his collaborators 

 as follows : — Group A {Trypanosoma hrucei group), including T. brucei 

 and T. gambiense ; Group B {T. jpecorum group), including T. pecorum 

 and T. simioe ; Group C [T. vivax group), including T. vivax, 

 T. ca.prae and T. unifornw. The forms in group A develop in the intestine 

 of the tsetse-fly, then pass into the salivary glands, where they develop 

 into infective forms ; this is the only group in which the salivary 

 glands are invaded. Those of group B , after developing in the intestinal 

 tract of the fly, become infective in the salivary duct, but never invade 

 the salivary glands. The T. vivax group develop first in the labial 

 cavity of the proboscis and later in the salivary duct or hypopharynx ; 

 no part of the development takes place in the intestinal tract or in the 

 sahvary glands. It is considered that this grouping may ultimately 

 require some modification. 



All three groups occur in Rhodesia, T. brucei, T. pecorum and 

 T. vivax all having been isolated from cattle, T. pecorum being by far 

 the most abundant. These are all true parasites of both mammals 

 and tsetse-flies, but just as only a comparatively small number of 

 mammals are true hosts of any one species of these trypanosomes, so 

 only a small number of flies, and all of them of the genus Glossina, act 

 as true hosts. In a district where T. pecorum and Glossi'na morsitans 

 are both common, only comparatively few individuals of either mam- 

 mals or flies would be found to harbour trypanosomes. Trypanosomes 

 that have been imbibed by a blood-sucking fly suffer various fates, 

 according to the nature of the fly and the nature of the trypanosome. 

 For example, T. brucei, imbibed by Glossina, may be infective for some 

 18 hours and then degenerate and lose their infectivity and perhaps 

 disappear altogether from the fly. They may, on the other hand, 

 multiply in the alimentary canal of the fly, the new forms passing 

 eventually into the salivary glands and regaining infectivity. When 

 imbibed by non- susceptible flies, the trypanosomes degenerate after 

 some hours, lose their infectivity and eventually disappear. A fly may 

 act as a transmitter of trypanosomes in three ways. It may be a true 



