Evaluation of a fluorescence-polarization assay for the diagnosis of bovine brucellosis in Mexico

A homogeneous fluorescence-polarization assay (FPA) was used for the serological diagnosis of bovine brucellosis in Mexico. The assay uses O-polysaccharide prepared from Brucella abortus Lipopolysaccharide (20-30 kDa) conjugated with fluorescein isothiocyanate as a tracer. To measure the fluorescence polarization, a FPM-1 fluorescence-polarization analyzer was used with the procedure described by Nielsen et al. (1996b). A cut-off value of 90 millipolarization (mP) units was used for testing 560 bovine sera from different areas of Mexico. (305 positive sera and 255 negative sera according to the complement fixation test; CFT.) Some were tested with the Rose Bengal plate (RB) test (n = 490) and some with the rivanol-agglutination (RN) test (n = 190). Sensitivities were 98.3%, 99.3% and 99.0%, and specificities were 68.8%, 55.4% and 96.9%, respectively, for RE, RN and FPA. The FPA gave a kappa coefficient of agreement with respect to CFT of 0.96, while RE and RIV (relative to the CFT) gave coefficients of 0.70 and 0.61, respectively. Finally, ROC analysis suggested a cut-off value which agreed with the one recommended in the test procedure. We concluded that FPA is a suitable test to be used instead of the CFT in Mexican conditions. (C) 1999 Elsevier Science B.V. All rights reserved.