Immunogenicity, safety, residual virulence, and efficacy of classical and new candidate vaccines against bovine brucellosis
Brucellosis, vaccination, RB51, S19.
Brucellosis is a chronic disease that affects several animal species, including humans, cattle and buffalo, and has worldwide distribution. Brucella abortus is the main species causing bovine brucellosis and leads to several economic losses, mainly due to abortions, stillbirth and infertility. In humans, brucellosis is a chronic and debilitating illness and is transmitted through ingestion of unpasteurized milk and dairy products or through contact with fetuses and abortion products from infected animals. Vaccination of young bovine females (between 3 and 8 months) with S19 or RB51 live strains is one of the major measures for brucellosis control worldwide, aiming both human and animal health. However, although the two vaccine strains have been widely used, they confer only 60-70% of protection against infection and abortion, value still far from being considered as ideal. In addition, many aspects of bovine vaccination with S19 and RB51 remain still unclear as whether there is or not an ideal age at vaccination for improving immune response; the innate immune response after vaccination and its relationship with activation of adaptive immunity and memory; and the effectiveness (field efficacy) of these strains. Furthermore, these vaccines have certain disadvantages. S19 is a smooth vaccine strain, and thus, vaccine-induced antibodies interfere with serological tests, preventing differentiation between vaccinated and infected animals. RB51, on the other hand, is a rough mutant and does not induce detectable antibodies in serological tests, but it is resistant to rifampicin, complicating the treatment of human cases caused by vaccination accidents. Therefore, besides detailing the aspects related to vaccination with S19 and RB51, proposing alternative vaccine strains without the mentioned disadvantages is important for advancing the control and eradication of the disease and for the health of the human population. Given that, the objective of these thesis is to evaluate immunogenicity, safety, residual virulence, and efficacy of classical and new candidate vaccines against bovine brucellosis.