To continue to exist, a bacterial pathogen must reproduce and be disseminated among its hosts. Thus, an important aspect of bacterial disease control is a consideration of how reproduction and dissemination of the organism occur. One must identify components of bacterial dissemination that are primarily responsible for a particular disease. Control measures should be directed toward that part of the cycle which is most susceptible to control the weakest links in the chain of disease process. Reducing or eliminating the source or reservoir of infection, breaking the connection between the source of the infection and susceptible animals and reducing the number of susceptible animals by raising the general level of herd immunity with immunization are three main kinds of control measures against bacterial diseases.