Evaluation of various ELISA kits for the detection of antibodies to M-avium subsp paratuberculosis in cattle

Blood samples were taken from 20 cows known to be faecal excretors of M. avium subsp. paratuberculosis and maintained in three chronically infected herds. A further 78 blood samples collected from these cows before faecal excretion was evident were also available. The sera were tested in four ELISAs for the detection of antibodies to M. avium subsp. paratuberculosis. At the time of shedding positive results were recorded as follows: IDEXX/CSL-ELISA 14 out of 20, HerdCheck-ELISA 17/20, Svanovir-ELISA 19/20 and the ELISA from the Pourquier Institute 20/20. All four testing systems detected positive reactions before confirmed excretion of the bacterium, but all gave the highest percentage of positive reactions after excretion was detected. Based on positive and questionable reactions during the period before excretion of the bacterium, the Svanovir-ELISA showed greatest sensitivity. The specificity was estimated by the examination of samples from 12 cows from each of 8 herds demonstrated to be free of paratuberculosis. Negative reactions were recorded in 94 of the 96 animals in the HerdCheck-ELISA, in 95 in the CSL-ELISA, in 78 in the Svanovir-ELISA and in all 96 animals in Pourquier-ELISA. An inconclusive result was recorded in nine animals in the Svanovir-ELISA, but none in the other tests. The Svanovir-ELISA was most suitable for detecting infected animals for control programmes because of its sensitivity, especially before faecal shedding commences. As this test produces some false positive results, the culling of animals should not be done until other confirmatory tests are conducted.