The relationship between the brucellosis card test and the complement fixation test used in the brucellosis eradication scheme

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Abstract
Widespread use of the brucellosis card test (BCT)and the complement fixation test (CFT) in the New Zealand Brucellosis Eradication Scheme has enabled various relationships between the tests to be studied. The number of CFT positive cattle which are also BCT positive is highest at initial herd tests and lowest at accreditation tests. When the prevalence of brucellosis within herds is more than 10% as measured by the CFT, 82% of all BCT positive samples are CFT positive and 17% of all CFT positive samples are BCT negative, whereas at low levels of infection (less than 1.0% CFT positive cattle in herd), only 38% of BCT positive samples are CFT positive and 43% of CFT positive are BCT negative. Sera strongly positive to the BCT are more likely to be CFT positive than sera which are weakly agglutinogenic. The probability of an animal that is BCT positive being CFT positive bearsno rela-tionship to the number of previous occasions on which that animal has been BCT positive and CFT negative. The results show that the BCT correlates well with the CFT when the number of CFT reactors within herds is high. As the CFT reactor rate declines, the degree of correlation with the BCT diminishes. This is probably due to the effect of strain 19 vaccination and the relative sensitivity of the tests to the various antibody classes.