Bovine tuberculosis and its control / by Veranus Alva Moore.

  • Veranus Alva Moore
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Bovine tuberculosis and its control / by Veranus Alva Moore. Source: Wellcome Collection.

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    The time necessary for a tuberculous cow to infect a large percentage of the cattle in the herd depends upon the rapidity with which the lesions in the infected animal develop to the stage where the tubercle bacteria are thrown off. There is a great difference in the length of time required for this de¬ velopment. In some cases the tuberculous areas become surrounded with a wall of fibrous tissue which checks the growth and the animal may never show evidence of its pres¬ ence. In other animals the infection may result in the rapid spread of the disease within the body and in the course of a few weeks or months tuberculous areas may discharge into some channel of excretion and the organisms be eliminated with either the saliva, feces, uterine discharges or the milk. It is impossible, therefore, to predict when a cow that reacts to tuberculin but appears to be perfectly well physically will spread the virus. This difference in the rapidity with which the disease develops depends upon the virulence of the infect¬ ing organism and the resistance of the animal. Pathogenic bacteria such as those of tuberculosis are not always possessed of the same degree of disease producing power. The resisting power of different individuals and even of the same individual under different conditions varies. It is impossible in the natural course of infection to determine the degree or extent of either of these factors. If this phase of the disease is under¬ stood it will explain why some animals that react continue to remain apparently well, while others develop physical signs of the disease and infect many individuals in the herd within a period of a few months. While these facts pertain to the nature of the disease, they are important in this con¬ nection to explain why some herds become infected rapidly and others more slowly or not at all after the introduction of a reacting animal or animals. Economic Importance. It is difficult to estimate the loss from bovine tuberculosis. There are many ways in which it operates financially against owners of livestock. Briefly stated, they are as follows:
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