320 



INFECTIOUS DISEASES 



Vaccination of the exposed or susceptible animals should 

 be practised. On farms where the disease exists it may be neces- 

 sary to vaccinate the young animals (less than two years of age) 

 once or twice every year in order to prevent the disease. Medic- 

 inal treatment is unsatisfactory. 



Texas or Tick Fever. — Tick fever is an infectious disease 

 of cattle. It is caused by an animal organism that is present in 

 the blood, and is conveyed from the animal that is host for the 

 tick fever parasite to the non-infected animal by a tick (Figs, 

 120 and 121). 



Tick fever was introduced into the southern portion of the 



Fig. 120. — Cattle tick (male). Fig. 121. — Cattle tick (female). 



United States through importation of cattle by the Spaniards. 

 Previous to the establishing of a definite quarantine line between 

 the permanently infected and the non-infected sections, heavy 

 losses among northern cattle resulted through driving and ship- 

 ping southern cattle through the northern States. The specific 

 cause and the part taken by the tick in its distribution were 

 not discovered until lS80-'90. Smith recognized and discovered 

 the specific cause of the disease, and Kilborn and Salmon proved 

 by a series of experiments that the cattle tick was respon- 

 sible for the transmission of the disease from animal to animal. 

 Tlie specific cause of tick fever is a protozoan parasite, Piro- 



