Evaluation and use of a serological assay for the detection of antibodies to Lawsonia intracellularis in swine

Porcine proliferative enteropathy (PPE) is a common and economically important gastro-intestinal disease of swine caused by the intracellular bacterium, Lawsonia intracellularis. Conventional tests to detect antibody responses to L. intracellularis include the immuno-peroxidase monolayer assay (IPMA), immuno-fluorescent antibody test (IFAT) and a lipopolysaccharide ELISA (LPS-ELISA). These tests are not commercially available. Therefore, objective of this study is to evaluate the performance of a commercial L. intracellularis blocking ELISA. Performance of the commercial ELISA was compared to the IPMA and LPS-ELISA using serum from experimentally infected animals (N = 40). The prevalence of L. intracellularis sero-positive animals was assessed by comparing suspect and randomly selected sera (N = 394). The commercial ELISA, IPMA and a non-commercial lipopolysaccharide (LPS) LPS-ELISA showed a 95% correlation when tested using experimentally derived known status samples. When compared to the IPMA the sensitivity of the commercial ELISA was 91% while the specificity was 100%. Therefore, the diagnostic sensitivity and specificity of the commercial L. intracellularis ELISA was comparable to the LPS-ELISA and IPMA. A comparison of suspect and randomly selected field samples with the commercial ELISA indicated that L. intracellularis sero-positivity is widespread and does not correlate with possible disease status