Mucosal and systemic humoral responses after experimental Brucella abortus challenge in non-vaccinated or RB51-vaccinated elk

Unvaccinated elk and elk inoculated with Brucella abortus strain RB51 were used (RB51) (n = 8/trt). Pregnant animals were conjunctivally challenged during pregnancy with B. abortus strain 2308 (2308). Sera, conjunctival fluid, and fecal samples were obtained and evaluated for IgG and IgA antibody responses. Animals were necropsied either within 1-3 weeks or at 14 to 17 wks after parturition. No difference (P > 0.05) in abortion or infection after experimental challenge was observed between treatments. Both treatments demonstrated seroconversion on standard tube agglutination (STAT), fluorescence polarization assay (FPA) and IgG ELISA but vaccinates demonstrated significant reductions in humoral responses at later sampling times. Elevations in IgG and IgA responses to 2308 and anamnestic IG responses to RB51 were detected in conjunctival fluid. Our data suggests that vaccinated elk demonstrated more rapid declines in IgG humoral responses after infection. Although serum STAT responses demonstrated minimal declines in both treatments, we observed reduced FPA and ELISA responses in vaccinates in later sampling times. Detection of brucellosis titers in elk is used to define the borders of designated surveillance areas where enhanced surveillance of domestic livestock is conducted and absence of seropositive responses in infected elk on standard serologic tests could enhance risk of disease transmission to cattle. This work provides new information on regulation of humoral responses of naïve and previously exposed elk after infection. Reductions in brucellosis titers of RB51 vaccinates after experimental infection has been observed in cattle and suggests anamnestic influences on elk humoral responses despite persistence of Brucella infection.