482 INFECTIOUS DISEASES DUE TO PROTOZOA 



(b) Boophilis (or margaropus) annulatus (American, 

 Australian, East Asian and South European piroplasmoses) . 



(c) Rhipicephalus appendiculatus (East Coast fever). 



(d) Dermacentor retieulatus (biliary fever) . 



(e) Rhipicephalus bursa (malarial fever of sheep). 

 Texas Fever. — {Piroplasmosis of Cattle. Southern Cattle 



Fever, Tick Fever). — Definition. — Texas fever is a specific 

 blood disease of cattle, due to the protozoon Piroplasma 

 bigeminum, and characterized by fever and hemoglobiniuia. 

 The causal germ is transmitted by ticks. 



Occurrence. — The disease is indigenous to districts infested 

 with certain varieties of the cattle tick. In the United 

 States Texas fever exists permanently in the southern states. 

 In the North, due to the cold winters which kill the ticks, 

 only sporadic outbreaks take place in the summer season, 

 the infection being carried from the South by ticky cattle. 

 Native southern cattle are tolerant to the disease, but 

 northern cattle brought South are very susceptible. The 

 disease also occurs in Australia, South America, India and 

 throughout Europe (different types) . Before the recognition 

 of the tick as a carrier of the infection, and the consequent 

 establishment of a Texas fever quarantine line across the 

 United States, the disease practically prevented the inter- 

 changing of northern and southern cattle. 



Etiology. — The cause of Texas fever is the protozoon 

 Piroplasma bigeminum. The transmitter of the infection 

 is the cattle tick of which there are several varieties. In 

 the United States the Margaropus annulatus is the carrier; 

 in Europe the Ixodes ricinus, in South America and Australia 

 the Boophilus argentinus and australis, and in South Africa 

 the Boophilis decoloratus and appendiculatus. 



The Piroplasma bigeminum is found in the red blood 

 corpuscles during the fever stage of the disease. They are 

 pear-shaped or round and usually occur in pairs. Depending 

 upon the number of protozoa introduced, the type of the 

 disease may be severe (acute) or mild (chronic). Dm:ing 

 the height of the Texas fever season (late in August, early in 

 September) the acute form prevails, while earlier than August 

 and later than September the milder, chronic type is met 

 with. 



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