AFRICAN TRYPANOSOMIASIS 135 



infective trypanosomes. Should tliis district become repopulated the 

 epidemic undoubtedly would come back again. 



Groups (B) and (C). 



None of these attacks man, hence little will be said about them. 



Group (B). 

 T. pecorum. 



Morphology. 



It causes the most important trypanosome disease of domestic 

 animals in Central Africa. 



It is the smallest of all pathogenic trypanosomes, being 9 — 18 /a 

 long. It is short and stout. 



The contents of the cell are homogeneous. 



The nucleus is oval and centrally placed. 



The kineto nucleus is small, round, situated towards the posterior 

 extremity, and may appear to project beneath the edge of the organism. 



The undulating membrane is simple. There is no free f^agellum. 



Pathogenicity. 



It is a disease of herds, horses, donkeys, oxen, goats, sheep and 

 pigs. Some attacked recover. 



It readily loses its virulence by passage through certain other 

 animals. If a trypanosome, infective to the monkey or dog, &c., 

 passes through a goat, it loses its power of infectivity for the monkey 

 and dog, &c. 



T. nanum is really a strain of T. pecorum. 



It is not so rapidly fatal to horses, donkeys and mules. 



In Nyasaland two-thirds of the cattle were lost and seven-eighths 

 of the goats. 



Carriers. 



The Glossina morsitans. The Tabanidae. 



4'6 per 1,000 tsetses were infected by the T. pecorum. 



Once a herd is infected, then ordinarv cattle or buffalo flies — the 

 Tabanidae, may spread it. These flies come and go in swarms, during 

 which visits they are real pests to cattle. 



The cattle feed at the hottest time of the day and crowd for self- 

 protection, hence conditions are very favourable for mechanical trans- 

 mission. When diseased members of a herd are removed, the disease 

 seems to cease when the Tabanidae and not the Glossina morsitans are 

 present. 



Between 1908-1913 some 2,500 to 3,000 head of cattle died in the 

 Barotse Reserve in Northern Rhodesia, though no Glossina morsitans 

 was present. 



The mortality begins in February and ceases in June each year. 



