Serodiagnosis of neosporosis in individual cows and dairy herds: A comparative study of three enzyme-linked immunosorbent assays

Abstract

The performance of three enzyme-linked immunosorbent assays (ELISA) for detection of antibodies to Neospora caninum in bovine sera was evaluated by using various categories of sera. Two commercial ELISA methods, one based on chemically fixed intact tachyzoites and one based on a sonicate lysate of whole tachyzoites, were compared with an in-house ELISA based on a detergent lysate of whole tachyzoites. A brief description of the development of the latter ELISA is also given. There was good agreement among all three tests with regard to postabortion sera. By using acute-phase abortion sera from cows with confirmed N. caninum-induced and non-N. caninum-induced abortions, satisfactory levels of sensitivity and specificity were calculated for all tests. In addition, similar test results were obtained with postpartum samples from dams and calves. However, considerable differences were found between test results of sequential samples and cross-sectional and total-herd samples. Apparently, these discrepancies were due to different sensitivities of the tests for detection of low antibody levels in chronically infected animals. It is suggested that these differences were primarily due to the use of different antigens and different test sample dilutions. It is concluded that all tests are applicable as an additional diagnostic tool in cases of abortion in cattle and for monitoring of congenitally infected calves. For herd screening, the lysate-based ELISAs appear to be more adequate because of their higher sensitivities.

FIG. 1

Precolostral N. caninum antibodies (ELISA test A) in 20 calves compared with serum and colostrum antibodies of their dams, which had histories of N. caninum abortions (colostrum samples 4 and 14 are missing).

FIG. 2

Profiles of antibodies to N. caninum, as determined with three different ELISAs, in two congenitally infected calves (calves 1 and 2) and two calves (calves 3 and 4) which received colostrum from N. caninum-seropositive dams.

FIG. 3

Profiles of immune response to N. caninum, as determined with three different ELISAs, in two cows which aborted during an abortion storm.

FIG. 4

Profiles of immune response to N. caninum in four cows that aborted, as determined with three different ELISAs during 1 to 2 years postabortion. These cows were from herds in which abortions were sporadic.