450 VETERINARY BACTERIOLOGY 



from 80 per cent, or more in some outbreaks to a small percentage 

 in others. 



Immunity. It is probable that agglutinins are formed, but the 

 difficulty of getting suspensions of the spirochete is so great that 

 the question has not been adequately tested. Immunity is 

 developed by an attack of the disease followed by recovery, but 

 to what agencies this is due is not certainly known. Marchoux 

 and Salimbeni heated blood from infected fowls for five minutes at 

 55, and succeeded in establishing immunity by its injection. 



Transmission. The disease is commonly transmitted from one 

 fowl to another by the ticks Argas persicus, Argas miniatus, and 

 possibly Argas reflexus. The louse is believed also, by Balfour, 

 to be an intermediary host. The latter author found that spiro- 

 chetes could be demonstrated in the salivary glands of the tick in 

 fourteen days after injection. The necessity for a definite incuba- 

 tion period has not been shown. 



Spirochaeta theileri 



Synonyms. Spirillum theileri; Spirillum ovina; Spirochceta 

 ovis; Spirochceta equi. 



Disease Produced. Spirillosis in cattle, sheep, and horses. 



Theiler, in 1902, discovered a spirochete in the blood of cattle 

 in South Africa. It has been found since that time in Cameroon, 

 East Africa, and Annam. The organism is 0.25 to 0.4 p by 10 to 

 30 ^. It resembles the preceding morphologically. The disease 

 is a benign infection, and the organisms soon disappear. It is 

 transmitted by the bite of a tick (Rhipicephalus decolor atus) . 

 Theiler, in 1904, reported the occurrence of a spirochete similar 

 to Spirochceta theileri in the blood of sheep in the Transvaal. 

 It was later found in northern Africa. Novy and Knapp have pro- 

 posed the name Spirillum (Spirochceta) ovis for this form. The 

 same investigator described a spirochete associated with a disease 

 of the horse in South Africa, and later it was reported from the 

 west coast. Novy and Knapp term this Spirochceta equi. Todd 

 and others, by cross inoculations, have demonstrated that these 

 organisms from the horse, sheep, and ox all belong to the same 

 species. 



