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

A homogeneous fluorescence-polarization assay (FPA) was used for the serolo gical diagnosis of bovine brucellosis in Mexico. The assay uses O-polysacch aride prepared from Brucella abortus Lipopolysaccharide (20-30 kDa) conjuga ted with fluorescein isothiocyanate as a tracer. To measure the fluorescenc e polarization, a FPM-1 fluorescence-polarization analyzer was used with th e procedure described by Nielsen et al. (1996b). A cut-off value of 90 mill ipolarization (mP) units was used for testing 560 bovine sera from differen t areas of Mexico. (305 positive sera and 255 negative sera according to th e complement fixation test; CFT.) Some were tested with the Rose Bengal pla te (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 ka ppa 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. Fin ally, ROC analysis suggested a cut-off value which agreed with the one reco mmended 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.