Evaluation of fluorescence polarization assay for the diagnosis of brucellosis in cattle and buffaloes in India

Abstract

Fluorescence polarization assay (FPA) was evaluated for serological diagnosis of brucellosis in cattle and buffaloes. Sera samples from 1397 cattle, comprising 120 indirect ELISA (iELISA) positive and 1277 iELISA negative; and 937 from buffaloes (88 iELISA positive and 849 iELISA negative) were tested by Rose Bengal test (RBT) and FPA in parallel. Receiver operating characteristic (ROC) curve was used for evaluation of FPA, using iELISA as gold standard to determine the cut-off offering the highest performance index (PI) and to compare its performance with RBT. In cattle, sensitivity (Sn) and specificity (Sp) of FPA were 46.7% and 96.6% respectively at a cut-off of 75 millipolarization (mP) in relation to iELISA, while Sn and Sp of RBT were 35.8% and 99.6% respectively. In buffaloes, Sn of FPA was 47.7% and Sp was 96.7% at a cut-off of 77.1 mP, whereas Sn and Sp of RBT were 44.3% and 99.2% respectively in relation to iELISA. McNemar’s chi-square test for independent data (with Yates’ correction) revealed that there was no significant difference in the proportion of positive samples between the FPA and RBT in cattle and buffaloes. Results indicated that FPA is as efficient as RBT for diagnosis of brucellosis. FPA may be preferred over RBT because of its characteristic of cut-off adjustments useful in different epidemiological situations and its potential application in field. However, further study with large number of known positive samples would be required for endorsement of FPA as a routine diagnostic test under the field condition.