The authors reviewed over 50 publications in which the sensitivity and specificity values of assays used for the detection of exposure to Brucella abortus had been examined. The sum of the sensitivity and specificity values for each test was averaged to give a performance index (PI) and allow for a comparison between the different methodologies. A score of 200 was perfect. Based on the PI, the buffered antigen plate agglutination test (BPAT) rated highest (PI = 193.1) among the conventional tests. This indicates better accuracy than the other conventional tests including the Rose Bengal test (PI = 167.6) and the complement fixation test (PI = 172.5). Overall, the primary binding assays, including the fluorescence polarisation assay (PI = 196.4), the indirect enzymelinked immunosorbent assay (PI = 189.8) and the competitive enzyme-linked immunosorbent assay (PI = 188.2), were more accurate than the conventional tests, except for the BPAT. In addition, a fee comparison suggested that the primary binding tests were price competitive with conventional tests for the diagnosis of brucellosis and, therefore, had a better combined cost/efficiency rating.

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Fluorescence polarization assay (FPA) is based on the rotational differences between a small soluble antigen molecule in solution (labelled with a fluorochrome) and the antigen molecule complexed with its antibody. A small molecule will rotate randomly at a rapid rate, resulting in rapid depolarization of light, while a larger complex molecule will rotate slower and depolarize light at a reduced rate. The rate change in depolarization can be measured. The FPA is a homogeneous assay which does not require removal of unreacted reagents and can, therefore, be performed very quickly and, given portable equipment, in the laboratory and in the field. The latter obviates the need for shipping samples and eliminates waiting for results, as well as reducing test costs. The FPA technology has been developed and validated for the serological diagnosis of brucellosis in cattle, swine, sheep, goats, bison, and cervids. Sufficient cross reactivity of the common epitopes of Brucella abortus, B. melitensis and B. suis O-polysaccharide (OPS) allowed for the use of a single antigen for all species of smooth Brucella and animals. The OPS prepared from B. abortus S1119.3 was conjugated with fluorscein isothiocyanate (FITC). The FPA was initially developed for testing serum; however, the technology has been extended to testing whole blood and milk from individual animals or bulk tank samples pooled from 2000 or fewer animals. The accuracy of the FPA equalled or exceeded those obtained using other serological tests such as the buffered antigen plate agglutination test (BPAT), the milk ring test (MRT), the complement fixation test (CFT), the indirect enzyme immunoassay (IELISA), and the competitive enzyme immunoassay (CELISA).

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The complement fixation test (CFT), competitive enzyme immunoassay (CELISA), indirect enzyme immunoassay (IELISA) and fluorescence polarization assay (FPA) were evaluated for the detection of antibodies to Brucella abortus and Brucella suis biotype 4 in caribou (Rangifer tarandus caribou), elk (Cervus elapus), red deer (Cervus elapus), and reindeer (Rangifer tarandus tarandus). When combining the data the FPA and the CELISA were determined to be the most suitable tests for serodiagnosis of Cervidae. The overall actual sensitivity of the CFT and the IELISA was 100%. The overall actual sensitivity for the CELISA and FPA was 99%. The overall relative specificity of the CFT (including treatment of anti-complementary data as positive or negative for analysis), the CELISA, the IELISA and the FPA were 65%, 93%, 99%, 99%, and 99%, respectively. The specificities of the buffered plate agglutination test (BPAT), the CFT, the CELISA, the FPA and the IELISA for 55 elk vaccinated with B. abortus strain 19 and tested 4 mo post vaccination were 14%, 31%, 51%, 84%, and 2%, respectively. The FPA is the diagnostic test of choice because it has sensitivity and specificity values comparable to the CELISA; it has the capability to distinguish vaccinal antibody and antibody resulting from exposure to crossreacting organisms such as Yersinia enterocolitica 0:9 from antibody to Brucella spp. in most cases; it is technically simple to do; it is adaptable to field use and it is relatively inexpensive.