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For many infectious diseases of ruminants vaccination is a feasible and desirable alternative to therapy. Vaccines that result in elevated herd immunity and disease prevention have important advantages in terms of cost effectiveness, animal welfare, and reduction of the environmental contamination that occurs when animals are treated with drugs and chemicals. Currently on the market are many efficacious and successful vaccines for ruminant diseases, but there are very few vaccines available for diseases of the mammary gland and skin. Undoubtedly the diseases that are easiest to control by vaccination have already been conquered; it is equally true that at the time such vaccines were developed the process was not easy! In the 1990s we have at our disposal new technologies such as molecular engineering and peptide synthesis. These technologies have dramatically improved our ability to synthesize usable quantities of antigens, yet many economically important diseases of the skin and mammary gland remain intractable. In this chapter we review progress that has been made with vaccines against such diseases and try to identify areas that may be profitable for future research endeavours.

Many important diseases of domestic animals have been rendered impotent by the development of safe and effective vaccines to prevent or ameliorate infection. Up to now, veterinary vaccines consisted mainly of killed or attenuated whole organisms. Vaccines of this type that are registered for use in the state of Queensland, Australia are listed in Table 1.1 (63,161). While not including many of the vaccines found in other countries, the list is indicative of current vaccine technologies. Vaccines such as these, which mostly contain whole pathogens, are usually highly immunogenic and utilize either no adjuvant or a simple adjuvant, such as alum or oil, to prolong the effect of the vaccine. The term adjuvant was first defined by Ramon (117) in 1925 as a substance that, when used in combination with antigen, enhanced levels of immunity beyond those developed with the antigen alone. A synopsis of the adjuvants currently available for veterinary vaccines was recently published by Vanselow (152).