Comparison of conventional agglutination tests and Fluorescence Polarization Assay for detecting antibodies to Brucella abortus in infected herds

LUTZELSCHWAB, CLAUDIA; GUTIÉRREZ, SILVINA ELENA; DIAZ, ALEJANDRA; ESTEIN, SILVIA

Buenos Aires

Congreso; Brucellosis 2011. 64th International Research Conference; 2011

Asociación Argentina de Microbiología

Bovine brucellosis has been a major disease in Argentina for many years, causing considerable economic loss. Control and eradication of this disease include elimination of infected cattle from herds and vaccination of female calves between 3 and 8 months of age. Official serological tests are based on detection of antibodies to the O-chain (OPS) epitopes of LPS (1).Conventional diagnosis includes the Buffered Plate Antigen (BPA) as screening test. Positive samples to this test are further assayed by seroagglutination test (SAT) and 2-mercaptoethanol (2-ME). By conventional serological tests it is not possible to discriminate antibody titres generated by vaccination or cross reactivity with other Gram (-) bacteria from those induced by natural field infections. Fluorescence Polarization Assay (FPA) is a specific and reliable test that is able to differentiate between vaccinated and infected animals (1,2). The purpose of this study was to compare the diagnostic performance of the conventional tests and the FPA in sera from different herds naturally infected with B. abortus (Santiago del Estero, Argentina). One hundred thirteen serum samples from cattle were tested in BPA and SAT/2-ME and FPA tests. Agglutination tests were performed and interpreted according to the procedures recommended by the Servicio Nacional de Sanidad Animal y Calidad Agroalimentaria (SENASA). SAT and 2-ME tests were performed in parallel. Sera with titres of 200 in SAT and/or 50 in 2-ME were considered positive. FPA was conducted with a commercially available kit and a protocol modified for microplates. Sera were considered positive if having a result of 105 mP or higher. From 37  positive samples in the conventional agglutination test, 27 (73%) were positive in the FPA and 10 (27%) were negative. All of 9 of the samples that were suspicious in the conventional test were negative in FPA. The high percentage of false positive reactions in the conventional agglutination test that were evident in this region of Argentina could be minimized by the implementation of the FPA assay (1,3).  The possibility of processing multiple samples in one plate is an additional advantage over the test performed in single tubes. (1) Nielsen K. (2002) Veterinary Microbiology 90: 447-459 (2) Nielsen K. y col. (1998) Veterinary Immunology and Immunopathology  66: 321-329 (3) Giménez P. y col. (2005) Revista Colegio Veterinarios de la Pcia. de Bs. As. 36: 39-42