Johne's disease (JD), caused by Mycobacterium avium subsp. paratuberculosis(MAP), has a significant economic impact on the US dairy cattle industry. Use of enzyme-linked immunosorbent assays (ELISA) to identify cattle for further fecal culture testing or for culling is listed as a recommended method for JD control in dairy and beef herds. However, several recent reports estimated diagnostic sensitivities of currently available ELISAs to be only 13.5 to 27.8%. For example, by using a Bayesian non-gold standard analysis, the diagnostic sensitivities of two current ELISAs were estimated to be 26-27%. Recently, it was predicted that if the diagnostic sensitivity of currently available ELISAs could be improved to 80%, then their use could result in an effective reduction of JD prevalence, higher level of milk production, and higher annual net revenue per cow.

We developed a novel ELISA, called EVELISA, for the detection of MAP infections in cattle and is highly sensitive identifying 97.4% of fecal-culture positive cattle compared to a currently marketed ELISA that identified 50%. However, when 37 serum samples from a herd with a high rate of false-positives were tested by the EVELISA as well as a currently available ELISA, both ELISAs found more than 70% of the samples to be positive for JD. The false-positive rate of the EVELISA was reduced significantly to 26.1% when the serum samples were pre-absorbed with M. phlei. By using the fecal culture method as the gold standard, empirical diagnostic sensitivity of the EVELISA using M. phlei absorption (absorbed EVELISA) was 97.1%, whereas that of a current ELISA was 48.5%. Moreover, a Bayesian non-gold standard analysis revealed that the absorbed EVELISA had a significantly higher level of diagnostic sensitivity (82%) than that of a current ELISA (22%). These data indicate that this novel ELISA is highly sensitive and may improve the effectiveness of JD control measures.