Although, the S19 and RB51 live vaccines used against brucellosis are safe, even in a few cases could cause disease in animals or humans (and personal associated with the cultivation of bacteria). In addition, by the inoculation of these vaccines, the ability to distinguish vaccinated from infected animals to microbes in natural ways is very difficult. Therefore, efforts to achieve a subunit vaccine, due to the problems of using conventional vaccines not in humans has risen; by this reason, brucellosis subunit vaccine development is one of the important research areas.
Since, a variety of protein and non-protein antigens of brucella, or a combination of them have been proposed as vaccine candidates. Induction of immunity against brucellosis; both immune responses are required, particularly cellular immunity. The characteristic of pure brucella antigen are not sufficient to induce these responses. Therefore, an effective subunit vaccine against brucellosis seems likely to be a combination of different brucella antigen [17, 21, 22].
In general, since the injection of pure LPS can induce a few antibodies, although it does not stimulate the immune system with high protection. This is due to the role of LPS as a thymus-independent antigen. The LPS was extracted from Brucella abortus S99, a smooth strain, which is used in the Pasteur Institute of Iran to produce antigens, and this component of the vaccine, was considered as the Hapten, due to the stimulation of the immune system. In order to correct the flaws of this vaccine, the OMP’s of Brucella abortus RB51 were used. Since, the candidates do not cause long-lasting immunity.
Attempts to develop vaccines for brucellosis have been done through the world. Despite all these efforts, no one has been able to develop an effective vaccine for the use in humans and animals with minimal side effects.
In order to develop an effective vaccine against brucellosis, now Smooth Brucella Strains:
B.abortus S19, B. melitensis Rev-1 and Rough Brucella strains: Brucella abortus RB51 are used in many countries [21, 23, 24].
Although S19 and Rev-1 have disadvantages of causing abortions in pregnant animals and are pathogenic in humans. However, more significant problems are the production of specific antibodies against O-LPS, and cross immunity seen in the conventional serological tests using S-LPS, 9, 10 and 23. Therefore, the best strain using to develop a brucellosis vaccine is Brucella abortus RB51 which, is a rough strain and does not have the disadvantages of the S19 and Rev-1 vaccine. In addition, studies have shown that the OMP’s of Brucella abortus RB51 strain are immunogenic. However, each one of them by itself is not an effective inducer of the immune system itself. However, they are all used together, they show a synergistic effect in the vaccine. In this study, all the 11 OMP’s were used [17, 25, 26].
SBA is superior to the ELISA method, because ELISA measures the antibody production that can only be achieved by a vaccine. Nevertheless, SBA, antigenicity and the serum bactericidal titers against bacteria can be achieved at the sane time, as desired. SBA was the main method for testing vaccine safety against Meningitis, and could likely be used to observe the vaccine immunity for brucellosis.
Despite the fact that Brucella is an intracellular bacterium, since the new developed vaccines are killed, it will not be a problem against the intracellular bacteria. Moreover, by the application of both LPS and the OMP’s of brucella abortus, the humoral and cellular immune responses to vaccines would be significant. The colony count of mice spleen clearly demonstrated the effectiveness of this vaccine compared to the control plate. Thus, indications are that the use of these two antigens may be useful in vaccine development.
Compared to the S19 vaccine, this vaccine did not show any sign of abortion. Bioassay in mice and rabbits did not show recurrence. Moreover, this vaccine does not have the risk of transformation of rough strains to soft strains. Since, there are risks of using cattle brucellosis vaccine in human. However, by using the combination of LPS and the OMP’s of brucella, it will be cleared.
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