206 TROPICAL MEDICINE AND HYGIENE 



containing the spirochaete. So far no other means of 

 infection is known, and it has already been mentioned 

 that attempts to transmit the disease by other parasites 

 than ticks, namely bugs, have been unsuccessful. 



Infected ticks can transmit the disease either immedi- 

 ately or by means of their progeny after an interval of 

 weeks and months ; the limit of the infectivity of such 

 ticks is at present unknown. Chromatin bodies have been 

 found by Leishman in the ova of these ticks, probably a 

 stage in the development of the spirochaete. 



There are certain further points of importance in con- 

 nection with the propagation of tick fever. These are 

 that ticks may transmit infection from animals which 

 they bite during apyrexial periods, when no spirochaetes 

 can be discovered in the blood ; that the blood which 

 has been passed through a Berkefeld filter remains infec- 

 tive ; and that a period of immunity follows infection. 



The first two of these facts indicate that infection may 

 be conveyed by some other possibly a developmental 

 form of the spirochnete, while these last may explain the 

 transmission of the disease from an apparently healthy 

 person. Experiments have been made with a view to 

 obtaining preventive and curative sera for tick fever. All 

 that can be said at present is that attempts to produce a 

 curative serum have failed, while a serum has been pro- 

 duced by the hyperimmunization of a horse, by means of 

 which the incubation period is lengthened and the attack 

 rendered milder in laboratory animals, though relapses 

 have not been prevented. 



Treatment. As in the case of relapsing fever, there is 

 no specific for tick fever and the treatment must therefore 

 be symptomatic. It should be on the same lines as that 

 indicated for relapsing fever. Atoxyl and mercury have 

 been tried for tick fever, but without much effect. 

 Salvarsan, as in all diseases due to spirochaetes, has a 

 markedly beneficial effect. 



Prophylaxis. As far as we know the disease is spread 

 only by the Ornithodorus moubata in nature (fig, 56). 



