Comparison of a competitive inhibition ELISA and the card agglutination test for detection of antibodies to Anaplasma marginale and Anaplasma centrale in cattle

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Abstract
ObjectiveTo compare a recently developed recombinant MSP‐5 competitive inhibition ELISA with a card agglutination test for detection of antibodies to Anaplasma marginale and Anaplasma centralein Australian cattle. Materials and methodsThe ELISA was compared with the card agglutination test using 208 sera from cattle in Anaplasma‐free herds, 86 sera from cattle experimentally infected with A marginale or A centrale and 757 sera from cattle in areas endemic for A marginale. ResultsThe specificity of the ELISA, based on testing 208 sera from cattle in Anaplasma‐free areas, was 99.5%, and the sensitivities for detection of antibodies to A marginale and A centrale in sera from the experimentally infected cattle were 98.0% and 100%, respectively. For the same sets of sera, the specificity of the card agglutination test was 98.6% and the sensitivities for detection of antibodies to A marginale and A centrale were 98.0% and 100%, respectively. For the 757 sera collected from cattle in areas endemic for A marginale, the agreement between the ELISA and the card agglutination test depended on the positive threshold selected for the ELISA. The maximum achievable agreement was 91.5% (kappa = 0.73; 95% confidence interval 0.66, 0.79). ConclusionWe conclude that the competitive inhibition ELISA is a useful alternative to the card agglutination test for detection of A marginale or A centrale infection in cattle. The assay should be particularly useful for epidemiological applications such as prevalence studies and control programs.