Evaluation of Erysipelothrix rhusiopathiae vaccines in pigs by intradermal challenge and immune responses

In a vaccine trial, pigs were challenged intradermally with eight E. rhusiopathiae strains of serovars 1a, 1b or 2 given concurrently. The strains were derived from six herds affected with vaccine breakdowns in 1997-1999, one herd without vaccine breakdown and a serovar 2 reference strain. Responses to two commercial bacterins (one implicated in the vaccine breakdowns), and two experimental bacterins (based on field isolates from affected herds) showed distinct differences in protection, particularly in clinical responses measured at 72 h. Less protection was afforded against serovar 1 challenge by the vaccine implicated in the vaccine breakdowns. Antibody and cell-mediated immune (CMI) responses were significantly different between treatments, and highlighted a similar post-vaccinal antibody response was produced against serovar 2 lysate by all vaccines, but only those providing significant protection against serovar 1 [corrected] produced significantly elevated antiserovar I lysate [corrected] antibodies. Vaccination in general significantly reduced CMI responses to the mitogens concanavalin A and phytohaemagglutinin. This experimental pig challenge system was readily able to confirm suboptimal performance of a commercial bacterin that had passed potency tests in mice but was associated with vaccine failure in commercial herds. This vaccine was also the most immunosuppressive to CMI responses associated with E. rhusiopathiae-specific and non-specific stimulation. The best vaccine response was associated with the highest mean serovar 1 antibody response and the highest CMI response (by lymphoproliferation assay) to serovar 2.