INFECTIOUS DISEASES OF CATTLE. ^ 429 



of Virginia from passing through the State; that these cattle infect 

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

 from Europe or the interior taken to the vicinity of the sea were 

 attacked by a disease that generally proved fatal. Similar observa- 

 tions have been made in regard to a district in the southeastern part 

 of Virginia, the eastern portion of North Carolina, nearly the whole 

 of South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, 

 the southern portion of Tennessee, and a large part of Arkansas, 

 Indian Territory, and Texas. It was the frequent and severe losses 

 following the driving of cattle 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 peculiar to Texas or even to the Gulf coast, but that it 

 extends far inland and northward almost to the southern line of Mary- 

 land. 



When cattle from other sections of the country are taken into the 

 infected district they contract this disease usually during the first sum- 

 mer, 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 become adult. 



When the infection is disseminated beyond the permanently infected 

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

 for susceptible animals until freezing weather. The infection then dis- 

 appears, and cattle may be driven over the grounds or kept in the 

 im -Insures 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. There 

 is some reason for believing that the infected district is gradually extend- 

 ing toward (he north, but more careful observations need to be made 

 before safe conclusions on this point can bo adopted. 



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

 IMM i< -IK < 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 disease when separated from infected pastures 

 by a fence. If, however, there is any drainage or washing by rains 

 across the line of fence this rule does not hold good. 



The investigations made by the Bureau of Animal Industry demon- 

 strate that the ticks which adhere to cattle from the infected district 

 are the chief means of conveying the infection to the l>odies of suscepti- 

 ble cattle. The infection, so far as we know, is not spread by the 

 saliva, the urine, or the manure of cattle from the infected district. In 

 studying the causation and prevention of this disease, attention must 



