The aim of this study was to investigate the efficacy of a combined live–dead vaccination protocol to protect sheep against Salmonella Brandenburg infection. Thirty ewes were randomly divided into two groups, one of which was vaccinated and the other acted as a control. The vaccinated group received a live modified Salmonella Typhimurium vaccine (given by eye-drop) followed 4 weeks later by a sub-unit preparation derived from S. Brandenburg (given subcutaneously with the adjuvant Quil A). Following challenge with wild type S. Brandenburg (4 weeks after the booster), 43% of the ewes aborted in the vaccine group as compared with 53% of the controls. However, a higher mortality rate was found in the vaccine group (43% vs 20%). Using an enrichment/selection procedure, S. Brandenburg was detected in the faeces of all challenged animals until 3 weeks post challenge. By 6 weeks and 9 weeks post challenge approximately 50% and 30% of animals respectively were shedding, irrespective of treatment. Following administration of the live primary and subunit (secondary) vaccines, levels of total IgG, IgG1 and IgM antibody (measured with an indirect ELISA) were significantly increased in comparison with the control group (P < 0.01). The cell-mediated immune response (interferon gamma from whole blood cultures) was also enhanced following use of the live attenuated vaccine (P < 0.01), but was much less pronounced after boosting with the subunit vaccine and following challenge. In summary, vaccination evoked immune responses but did not give protection to experimental infection with S. Brandenburg.
Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 157-162, 2005
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