A rebirth of interest and activity in vaccine development has occurred in recent years which is probably due to the persistence of threat to health by infectious diseases, as well as technological advances which have made possible new approaches to solve old problems. Most work being done today with vaccine development against diseases caused entirely or in part by bacterial toxins falls into the categories of, attenuated organisms (whether by classical means or application of newly developed genetic technologies), and/or toxin subunits (derived by genetic manipulations, peptide synthesis, or chemical modification of toxins). This review discusses some of these new approaches in general as well as specific examples of their application to several bacterial diseases whose pathologies involve toxins.
Marek's disease (MD) is one of the viral infections that attack poultry and are widespread throughout the world. Vaccination is widely used for the protection of chickens against outbreaks of MD, and commercial vaccines have been used since 1970. There are vaccines derived from three avian herpesvirus serotypes which are propagated in CEF or DEF cell cultures. Most of them are used successfully for vaccination against MDV and are effective and safe. In problem areas where the monovalent vaccine gives poor protection, the use of a bivalent or polyvalent vaccine is recommended for the successful prevention of virulent MDV.
Vaccination has played an enormous role in reducing brucellosis in many countries. It is certain to continue to be the preeminent factor in control of the disease in others. The search for an ideal vaccine continues. Live vaccines have proved to be superior to inactivated products. They are effective, inexpensive, and immunity is more persistent. The disadvantages of postvaccinal antibodies can be minimized by reduction of previously recommended doses and through use of supplemental diagnostic tests. These procedures now make entire population vaccination of great practical significance with many advantages over limited use of the strains 19 and Rev. 1. Adult animal vaccination should be much more extensive in many countries. A live B. suis strain 2 vaccine developed in China deserves much additional evaluation, including use in swine, for which no satisfactory vaccine exists. It is generally agreed that cell-mediated responses are the dominant aspect of immunogenesis. However, the correlates that have frequently been used--dermal hypersensitivity and lymphocyte stimulation in vitro--appear to be poor indices of cell-mediated immunity in brucellosis. Many studies have shown that postvaccinal antibodies do not predict subsequent immunity. There is a great need for simple in vivo or in vitro methods to measure CMI. While vaccination of humans may be useful in control of brucellosis in some high-risk occupations, the ultimate success is dependent upon reduction of this very important zoonosis in natural hosts. This is most effectively accomplished by widespread use of vaccination.
The eradication of pertussis as a worldwide disease is unforeseeable for the present and immediate future. Mortality and morbidity from clinical pertussis are still commonly reported, especially in underdeveloped countries where mass immunization programs are virtually nonexistent. To achieve control of the disease, a high level of immunization coverage is necessary, and pertussis WCPV still remains one of the most effective bacterial vaccines. But, primarily because of its reactogenicity for infants, much effort has been directed toward the characterization of bacterial components important in pathogenesis and for the development of acellular vaccines. Progress in the last decade has resulted in the production and use of such vaccines for routine vaccination, and their use in Japan, as well as the recent clinical trials in Sweden and several phase I/II studies in other countries, has shown that these preparations are safer than conventional WCPV, and equally effective, in preventing disease. The development of future acellular pertussis vaccines by gene manipulation may finally inspire public confidence for vaccine prophylaxis, eventually leading to eradication of the disease. However, the production and use of such sophisticated vaccines is dependent on many factors, and consequently conventional WCPV may still be used in many countries for several years to come.
