LECTURE XXXVIII 

 TEXAS OR TICK FEVERS 



This disease passes under a variety of names, such as acclima- 

 tion fever, red water, liloody murrain, etc. 



Economic importance. — The seriousness of tick fever as a 

 disease of cattle, and its bearing upon the southern cattle indus- 

 try, was not realized until recent years. 



Causes. — It has been established that the disease is caused by 

 a microscopic animal parasite, a protozoan {Piroplasma higemi- 

 num) which attacks the red cor- 

 puscles of the blood. Its multi- 

 plication in the blood is rapid 

 and its effects are destructive, in- 

 volving especially the red blood 

 corpuscles, which it destroys 

 rajiidly. 



Transmission. — So far as 

 known, the only natural means 

 of transmitting the causative 

 agent of this disease is the south- 

 ern cattle tick {Margaropus an- 

 nulatus).. Other species of ticks 

 attack southern cattle, but this is 

 the most common and is the only 

 one responsible for transmission 

 of the Texas Fever parasite. 



The ticks do not carry the pro- 

 tozoan directly from one in- 

 fected animal to another, but the female ticks develop on in- 

 fected animals and tlien transmit the Piroi)lasma in some form 

 to their progeny, which carry it to susceptible animals. 



Susceptibility. — Bovines alone seem susceptible to the dis- 

 ease, although the tick, which carries the infection, occasionally 

 infests horses and mules. Calves at birth as a rule have a high 



^This lecture contributed by Dr. Tait Butler. 



185 



Fig. 64. 



Female engorged. 

 annulatus (Riley). 



Tkxas Fever Tick. 

 {Pettit.) 



Margaropus 



