Serological crossreactivity in diagnosis of brucellosis in Balb/c mice following administration of bovine commercial vaccines containing Gram negative bacteria

Abstract

Control of Bovine Brucellosis in Argentina is based on vaccination of calves with B. abortus S19, and detection and slaughter of positive reactors. Screening tests for the diagnosis of this disease are BPA (Buffered Plate Antigen) and FPA (Fluorescence Polarization Assay). Both tests detect antibodies to the O-chain, which is the immunodominant epitope of LPS in smooth Brucella spp. and are susceptible to false positive results (1, 2). The aim of this work was to study cross reacting antibodies resulting from administration of commercial vaccines containing Gram negative bacteria that share antigenic determinants with Brucella spp. in the mouse model. Female BALB/c mice 6-8 weeks old were randomly distributed in nine groups (n=5) and vaccinated using different commercial immunogens. Booster was performed at 25 day. In addition, two positive control groups immunized with B. abortus S19 (n=6) and infected with B. abortus S544 (n=5) were included. Blood samples were obtained at 0, 7, 15, 40, 50 and 60 days after immunization. Sera were analyzed by BPA and FPA tests. Immunized mice with commercial vaccines gave positive results to BPA at different points during the experiment, but at the end all mice were negative. None of sera from vaccinated mice reacted in FPA. Mice from positive control groups remained positive to BPA throughout the experiment. Infected mice were positive to FPA while mice from B. abortus vaccine strain had variable results. Cross reaction antibodies were induced by vaccines containing mainly Pasteurella haemolytica (Mannhemia haemolytica), P. multocida, Haemophilus somnus (Histophilus somni), Campylobacter fetus fetus and Moraxella bovis. These results showed that certain bovine commercial vaccines were able to induce non specific serological reactions in conventional serological test of bovine brucellosis (BPA), but these reactions were observed for a variable period. False positive reactions can be minimized by using other tests such us FPA. This technique showed to be a reliable test to overcome occurrence of serological cross reactions in bovine brucellosis diagnosis (3).