Bacterial diseases are infectious in nature, i.e. they can be transmitted from one host to another. Outbreaks of infectious diseases are often compared with forest fires. Once a fire has spread through an area, it does not return until new trees have grown up. Outbreaks develop when a large population of susceptible animals is present. lf immunized animals are present in the herd, then outbreaks cannot occur until a sufficient number of young, non-resistant animals have been bred or non-immune animals from outside are introduced in the herd. The development of a bacterial disease is a complex process involving many factors. Many a time, control activities reflect compromises among alternatives. To proceed intelligently, one must identify components of the bacterial dissemination which are primarily responsible for a particular disease. Control measures should be directed towards that part of the cycle which is most susceptible to control the weakest links in the chain of disease process. The restriction of movement of animals suffering from, or exposed to, infection is one of the oldest tools known to preventive medicine. The principle of quarantine of domesticated animals was applied as early as roman times. The early detection of a disease in a population of animals- a herd of cattle, for example-is particularly useful in controlling certain chronic infectious diseases, such as mastitis, brucellosis and tuberculosis. Laboratory tests like agglutination test in pullorum disease, the tuberculin skin test for tuberculosis and chemical tests performed on milk to diagnose bovine mastitis are used for the detection of diseases in an animal population. Laboratory tests to confirm the existence of diseased animals in a population, followed by slaughter of the affected animals, have been of great value in controlling infectious and genetic diseases. Bovine tuberculosis has been eliminated from Denmark, Finland and Netherland and reduced to a low level in various other countries like Great Britain, Japan, United States and Canada by this method. The present book has been carefully compiled and edited to meet the long felt needs of increasingly number of students and researchers who have to deal with the different aspects of animal diseases. it is intended that the book will prove to be a valuable reference on veterinary medicine.
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