Evaluation of three competitive ELISAs and a fluorescence polarisation assay for the diagnosis of bovine brucellosis

• The accuracy of three C-ELISAs and FPA for the diagnosis of bovine brucellosis was evaluated and compared to usual tests.
• The most sensitive tests were FPA, C-ELISA1, and RBT and the most specific ones were CFT, SAT and RBT.
• The accuracy of C-ELISAs varied greatly depending on the kit used.
• New tests should not be used as single tests: their use in association with another test should be recommended.

Bovine brucellosis is an infectious disease of worldwide public health and economic importance. The usual tests for the diagnosis of this disease include the Rose-Bengal test (RBT), complement fixation test (CFT), serum agglutination test (SAT) and indirect ELISA. New tests such as competitive ELISAs (C-ELISA) and fluorescence polarisation assay (FPA) have been developed. However, C-ELISA may correspond to different protocols and a wide variation may exist in their diagnostic performance. The aim of this study was to evaluate three commercially available C-ELISA kits (C-ELISA1–3) and FPA for the diagnosis of bovine brucellosis and compare test performance with RBT, CFT, indirect ELISA and FPA. Sera submitted to EU laboratories in 2011 from 5111 adult cattle were tested. Individual test sensitivities (Se) and specificities (Sp) were estimated. Threshold assessment using the receiver operating characteristic method was also performed.The most sensitive tests were FPA (99.0%; 95% confidence interval [CI], 97.9-100%), C-ELISA1 (98.4%; 95% CI, 97.0-99.8%) and RBT (97.7%; 95% CI, 95.9-99.3%). The most specific tests were CFT (99.98%; 95% CI, 99.93-100%), SAT (99.98%; 95% CI, 99.93-100%) and RBT (99.89%; 95% CI, 99.79-99.99%). Among the new tests, none of the three C-ELISA kits studied could be recommended as a single screening test because of their low specificity, especially when used in a herd. C-ELISA3 could not be recommended as confirmatory test on individual animals to determine whether false positive serological test results had occurred.