318 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



others while they themselves are in perfect health, and that cattle 

 from Europe or the interior taken to the vicinity of the sea are at- 

 tacked by a disease that generally proves fatal. Similar observations 

 have been made in regard to a district in the southern part of the 

 United States. The northern limits of this area are changed yearly as 

 a result of the dissemination or eradication of the cattle tick along the 

 border, but the infected area has gradually decreased, owing to the 

 successful endeavors pushed forward to eliminate the ticks. 



It was the frequent and severe losses following the driving of cat- 

 tle from the infected district in Texas into and across the Western 

 States and Territories which led to the disease being denominated 

 Texas fever. It is now known, however, that the infection is not pe- 

 culiar to Texas or even to the United States, but that it also exists in 

 southern Europe, Central and South America, Australia, South Af- 

 rica, and the West Indies. 



When cattle from other sections of the country are taken into 

 the infected district they contract this disease usually during the first 

 summer, and if they are adult animals, particularly milch cows or fat 

 cattle, nearly all die. Calves are much more likely to survive. The 

 disease is one from which immunity is acquired, and therefore calves 

 which recover are not again attacked, as a rule, even after they be- 

 come adult. 



When the infection is disseminated beyond the permanently in- 

 fected district, the roads, pastures, pens, and other inclosures are 

 dangerous for susceptible animals until freezing weather. The in- 

 fection then disappears, and cattle may be driven over the grounds 

 or kept in the inclosures the succeeding summer and the disease will 

 not reappear. There are some exceptions to this rule in the section 

 just north of the boundary line of the infected district. In this 

 locality the infection sometimes resists the winters, especially when 

 these are mild. 



In regard to the manner in which the disease is communicated, 

 experience shows that this does not occur by animals coming near or 

 in contact with each other. It is an indirect infection. The cattle 

 from the infected district first infect the pastures, roads, pens, cars, 

 etc., and the susceptible cattle obtain the virus second hand from 

 these. Usually animals do not contract this disease when separated 

 from infected pastures by a fence. If, however, there is any drain- 

 age or washing by rains across the line of fence this rule does not 

 hold good. 



The investigations made by the Bureau of Animal Industry 

 demonstrate that the ticks which adhere to cattle from the infected 

 district are the only known means of conveying the infection to the 

 bodies of susceptible cattle. The infection is not spread by the sa- 

 liva, the urine, or the manure of cattle from the infected district. 

 In studying the causation and prevention of this disease, attention 

 must therefore be largely given to the ticks, and it now seems appar- 

 ent that if cattle could be freed from this parasite when leaving the 

 infected district they would not be able to cause the malady. The 

 discovery of the connection of the ticks with the production of the 



