Vr. Vanzini et al., EVALUATION OF AN INDIRECT ELISA FOR THE DIAGNOSIS OF BOVINE BRUCELLOSIS IN MILK AND SERUM SAMPLES IN DAIRY-CATTLE IN ARGENTINA, Preventive veterinary medicine, 36(3), 1998, pp. 211-217
An indirect enzyme-linked immunosorbent assay (ELISA) for Brucella abo
rtus antibodies detection in bovine milk and serum samples was validat
ed. The assays use B. abortus smooth lipopolysaccharide as antigen, im
mobilized on a polystyrene matrix; milk diluted 1:2 or serum diluted 1
:50, in a buffer containing divalent cation chelating agents EDTA and
EGTA thyleneglycol-bis-aminoether-N,N,N',N'-tetraacetic acid) to reduc
e non-specific reactions; and a mouse monoclonal antibody specific for
an epitope of bovine IgG(1), conjugated with horseradish peroxidase.
A total of 2646 sera and 2119 milk samples from cows older than 24 mon
ths were obtained from 12 brucellosis-free herds for at least the prev
ious 5 years. Milk samples were obtained in parallel with serum sample
s. The remaining 527 serum samples were from dry cows. All cattle were
vaccinated with B. abortus strain 19 between 3-10 months of age. Five
hundred and fifty-two milk samples and 562 serum samples were obtaine
d from 6 infected herds with abortions where B. abortus was isolated a
t least once no more than 6 months before sampling. The complement-fix
ation test (CFT) on serum samples was considered the gold standard. Se
rum samples were also tested with the official screening test: the buf
fered plate antigen (BPA) test. The cut-off point was determined using
receiver-operating characteristic (ROC) analysis. For milk samples, i
t was fixed at 36 percent positivity (PP) giving a sensitivity of 99.6
% with a 95% confidence interval (CI) of 98.6-99.9%.. The specificity
was 99.1% (CI 98.9-99.4%). For serum samples, the cut-off was fixed at
53 PP giving a sensitivity of 99.6% (CI 98.6-99.9%) and a specificity
98.6% (CI 98-99%). The BPA test showed a relative sensitivity of 99.6
% (CI 98.6-99.9%) and a relative specificity of 98.6% (CI 98.1-99%). O
ur results indicate that the indirect ELISA is a highly sensitive and
specific test and can be adapted to process a large number of samples.
(C) 1998 Elsevier Science B.V. All rights reserved.