Diseases, Ticks, and their Eradication. 141 



DISEASES, TICKS, AND THEIR ERADICATION. 



By Sir Arnold Theiler, K.C.M.G., Director of Veterinary 

 Education and Research. 



One of the results of scientific investigation into the cause of .stock 

 diseases contracted in the veld of South Africa Avas the cognizance 

 that ticks play an important role in their maintenance and proi)aga~ 

 tion. It is advisahle to review our knowledjjre concerning- these 

 diseases, as well as that of the life-history of the ticks which transmit 

 them. Such a review will illustrate the utility and necessity of 

 eradicating' ticks ; it will guide us in our recommendations of methods 

 to be adopted for their control and eradication. It will further be 

 demonstrated that it is possible to prevent disease and save cattle by 

 transferring the stock from an infected area into a clean one, 

 according to a carefully worked out method, based on accurate know- 

 ledge of the life-history of the tick. 



All tick-borne diseases are caused by micro-org-anisms present in 

 the blood stream. These organisms belong to diftejf nt groups ct blood 

 parasites, and are all visible under the microscope witli the exception 

 of one, the causal agent of heartwater in ruminants, wnich belongs to 

 tlie group of ultra-visible viruses. 



Biliary Fever of Horses. 



The cause of this disease in South Africa is NuttaUia cqin 

 (formerly called Piroplasvia equi). A similar disease caused by an 

 allied parasite, Babesia cahalli, is found in Europe. It has not yet 

 been definitely demonstrated whether the allied parasite is present in 

 Soaith Africa, but it may be expected to be found at any time. Our 

 biliary fever affects all equines. The disease, hovrever, varies some- 

 what in severity of symptoms in the horse on the one side and the 

 donkey and its hybrids on tlie other. It is laiown over the greater 

 ])ortion of South Africa; certain areas, however, i.e. parts of the 

 Karroo, seem tO' be exempt. Animals born and bred on the veld of 

 the infected parts, once they are grown uji, are not so liable to suffer 

 from the disease, and they do so only under specird conditions. This 

 observation is due to the fact that young equines (foals), although 

 they contract the infection as soon as they are turned into the veld, do 

 not readily die from tlie disease. They recover and acquire a con- 

 sideral)le amount of immnnity. The chief suffer.^r is the animal bred 

 either on uninfected farms or in stables, or imported from oversea. 

 The parasite that causes the biliary fever lives within the red 

 corpuscles of the blood, where it multiplies and subsequently invades 

 a smaller or greater number of other corpuscles. Its action is the 

 destruction of the red corpuscles, and the more j^arasites present or the 

 quickei' they multiply the more dangerous becomes the disease. The 

 destruction of the corpuscles becomes apparent in the anaemia whicli 

 follows. In the horse, however, this anaemia is bidden, so to say, by 

 fi bilious condition. The destrnction of the red corpuscles leads to 



