Disease Epidemics

In spite of good management, unexpected disease epidemics are seen in feedlot cattle. When feeding accidents occur, many animals can be affected suddenly, ie, within 1–2 days. In outbreaks of acute infectious diseases, such as infectious bovine rhinotracheitis, pneumonic pasteurellosis, or Histophilus meningoencephalitis, the first few cases are followed by a steady increase in the morbidity rate for several days and then a decline as the outbreak subsides 10–14 days after the index case.

In some cases, the diagnosis may be obvious (eg, carbohydrate engorgement caused by a feeding error). In other cases (eg, infectious diseases of the respiratory tract), the diagnosis may not be readily obvious, and a detailed epidemiologic, clinical, and laboratory investigation may be required. A complete investigation may require specialists from several disciplines. Every effort should be made to determine the specific source of the disease. The investigation should include a general description of the problem, a complete history of the disease outbreak (including details and date of index case, total number of sick animals, treatments, case fatality rate, population mortality rate, and vaccination history), and clinical examination of several affected animals (with appropriate samples) as well as necropsies. After the diagnosis is determined, the rationale for treatment is outlined. When outbreaks of infectious disease are encountered, the intensity of surveillance must be increased to detect new cases in the early stages of disease when response to treatment is usually good.

All of the details of the outbreak should be listed in chronologic order and then analyzed. Correlations can be made between exposure factors and the development of new cases during the course of the outbreak. Often, epidemiologic determinants that explain disease occurrence can be identified and the information used to control future episodes. A detailed report of the outbreak, outlining the conclusion and recommendations, should be prepared by the veterinarian and nutritionist and submitted to the owner.