Evaluation of the results of the ELISA reaction in the serologic diagnosis of bovine leukosis

Blood serum samples collected from two cattle herds were examined by the immunodiffusion test (ID), pseudotype neutralization test (PsNT) and ELISA procedure for the presence of antibodies to the bovine leukosis virus. The spectrophotometric readings of the ELISA procedure were evaluated on the basis of the arithmetical mean (means) and standard deviation (Sd) of the values obtained in negative controls. The examination of 208 samples of serums taken in the negative herd confirmed in all cases a negative reaction in the ID and PsNT tests. In all samples the ELISA reaction values remained within the range delimited by the relation of means + 3 Sd, which was defined as the threshold value of positive reaction. Out of the 223 serum samples of the positive herd, 132 samples were within the range below means and five of them were leukosis-positive in PsNT. Twenty-nine samples were within the range of means to means + 3 Sd; five of them were found positive in PsNT and three in the ID test. Sixty-two samples were above the threshold value of positivity; of these, positivity was confirmed in 58 cases by PsNT and in 55 cases by ID. As the results suggest, the ELISA procedure is suitable for the detection of animals positively reacting to bovine leukosis, to which special attention should be paid.