The modification and evaluation of an ELISA test for the surveillance of Mycobacterium avium subsp. paratuberculosis infection in wild ruminants

We found that the anti-bovine conjugate included in the IDEXX ELISA kit has limited affinity for elk, bison, and caribou IgG. Protein G showed good affinity for IgG of all three species, while anti-deer conjugate also bound elk and caribou IgG. Using Protein G with elk serum, a cut-off sample-to-positive (S/P) value of 0.22 was selected, resulting in a sensitivity and specificity of 73% and 90%, respectively, whereas, using an anti-deer conjugate with elk serum, an S/P cut-off value of 0.29 gave a sensitivity of 68%, with 100% specificity. Cut-off values for bison and caribou using the Protein G conjugate were 0.17 and 0.25 respectively.Due to incomplete reporting and a lack of test validation, it is difficult to critically appraise results of many sero-surveys that have previously been done for MAP in wildlife. Commercial ELISA kits may have limited or no capacity to detect antibodies from species other than for which they were developed. In order to generate reliable test results, it is essential to evaluate the test and perform modifications if deemed necessary. Despite the challenges inherent to wildlife diagnostics, we have shown that several methods can be used to improve confidence in test results.Mycobacterium avium subsp. paratuberculosis (MAP) causes granulomatous enteritis in ruminants that can lead to weight loss and emaciation, as well as diarrhoea in certain species [1]. MAP has been detected in wild ruminant species worldwide, and it is thought that all ruminant species are susceptible to MAP infection [2]. Although clinical disease, known as Johne’s disease, has only occasionally been described in wildlife, its impact may be under-estimated due to incomplete knowledge of the clinical progression of MAP infection in these species, non-specific clinical signs, and limited testing in these populations.Determining the infection status of wildlife is important to reduce the disease risks associated with translocation, to certify infection status for impor