PUBLIC HEALTH 37 



animals. Apart from this, the economic loss occasioned by 

 such affections of domestic animals is enormous, although it 

 is in great part preventable. 



A wide-spread disease of cattle in the southern part of the 

 United States, known as splentic fever, or "Texas fever," is 

 the most important insect-borne animal disease that occurs 

 in this country, and is particularly interesting since it was the 

 first disease of any kind shown to be carried exclusively by 

 insects or ticks. It occurs very generally throughout the gulf 

 states as far north as the thirty-sixth parallel of latitude and 

 is the cause of immense pecuniary loss to this region, not only 

 on account of the cattle lost, but as a result of the greatly 

 weakened condition of the animals in general. Southern 

 cattle are usually immunized by an attack at an early age, 

 but northern animals die in large numbers when exposed to 

 the disease. 



Smith and Kilborne showed in 1893, that the protozoan 

 blood-parasite, Babesia bigemina, which Smith had discovered 

 several years earlier to be the cause of the disease, is carried 

 by ticks. The common cattle-tick of the southern United 

 States, Margaropus annulalus, acts as the exclusive vector, 

 becoming infected during its period of engorgement when 

 feeding on the blood of a diseased animal and then transmit- 

 ting the Babesia through its eggs to the young ticks of the 

 next generation. These may feed on healthy animals the 

 next season, conveying to them the parasites that have been 

 handed down from the mother tick. 



Several similar diseases of cattle occur in other parts of the 

 world. In Africa, related forms of Piroplasma carried by ticks 

 are the cause of redwater, East Coast fever, Rhodesian fever, 

 and in various parts of the world other piroplasmoses have 

 been observed in many animals. 



Spirochsetosis in animals, due to organisms similar to those 

 producing relapsing fever, is well known. The most fa- 

 miliar example is probably a disease of fowls which is car- 

 ried by Argas miniatus, a common tick which infests these 

 birds. 



