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Disease is defined as a definite process having a characteristic progression of symptoms that may affect the whole body or any of its parts. Its cause, specific effects, and outcome may or may not be known. Infectious, metabolic, toxic, deficient, genetic and traumatic causes are examples of categories fitting the definition. Infectious processes frequently receive attention due in part to their ability to spread to other animals through various means.
Infectious processes are given "new or emerging" status for various reasons. New or relatively rare entities may become prevalent. Changes in existing infectious disease characteristics have resulted in new clinical signs of disease. Management changes resulting in new risk factor combinations have resulted in new infectious processes under predisposing circumstances. Seasonal severe weather conditions also have resulted in new infectious disease trends.
Completely new infectious agents are infrequently identified in the United States. Foreign animal diseases such as foot and mouth disease are not present in the United States and strict preventive measures are enforced. Surveys evaluating prevalence of known disease-causing organisms in cattle often reveal surprisingly high incidence rates. Presence of disease causing organisms in cattle populations frequently does not imply that disease will occur.
Several infectious diseases have received attention at varying levels recently. Their importance or future implications are often not known.