42 



The presence of Sfirillum theileri had been seen in animals suffering 

 from other infections as, for instance, Piroplasma mutans, Piroplasma 

 bigemimim., Trypanosome theileri. In the former two cases it is sometimes 

 difficult to say which wou.ld be the primary infection, especially when the 

 fact is considered that Sfirillum theileri remains in the blood of immune 

 animals. The appearance of the spirillum, together with trypanosomes, 

 must be considered as a breakdown of immunity of spirillosis. 



Conclusion. — The immunity obtained through the recovery from a 

 Sfirochaetosis infection is not complete ; the blood remains infective 

 and intercurrent fevers cause an increase of the parasites. 



IV.— EAST COAST FEVER {Theileria parva). 



East Coast fever is a disease in cattle due to the presence of Theileria 

 -parva, a parasite of the red corpuscles, which can so far only be introduced 

 into the system in the natural way by means of ticks. Thus the disease 

 is not inoculable, and all attempts to transmit it with blood by infusion 

 or injection of juice of internal organs have failed. In one of our experi- 

 ments, a young ox was infused during fifteen minutes with East Coast 

 fever blood ; there was no reaction due to this. The disease leads to a 

 mortality of 95 per cent. The recovered animals are known to be immune. 

 A number of eight oxen which had recovered in August, 1902, at 

 Komatipoort from East Coast fever, were exposed three and a half years 

 later at Sjamboks Kraal to natural infection ; none of these animals con- 

 tracted the disease. 



Conclusion. -T/ie immunity is complete concerning natural infection 

 and concerning time. 



The Blood of Immune Oxen. — Immune animals do not retain the 

 infection in the blood. This can be observed in practice where immune 

 cattle have survived the outbreak of East Coast fever, where subsequently 

 young, or new, fresh imported stock were running together on tick-infected 

 farms without ever showing an infection. Oxen which recovered in the 

 year 1902 from East Coast fever have been running since then with 

 susceptible cattle in tick-infected areas without transmitting the disease 

 to the susceptible ones. 



Experiments* to prove this were also undertaken by feeding brown 

 tick uymphae on oxen which had two years previously recovered from 

 East Coast fever, and placing the moulted adults on susceptible cattle. 

 In no instance did such ticks transmit the disease, hence it can safely be 

 concluded that the blood of East Coast fever immune cattle harbours no 

 longer the parasite of East Coast fever. 



Conclusion. — The blood of an ox recovered from East Coast fever does 

 not retain its infectivity. 



* Annual Report, G.V.B., Transvaal,, 1903-04, pages 93 and 94. 



